Weeds of Lawn and Garden: A Handbook for Eastern Temperate North America [Reprint 2016 ed.] 9781512815962

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WEEDS OF LAWN AND GARDEN

WEEDS OF LAWN AND GARDEN A HANDBOOK FOR EASTERN TEMPERATE NORTH AMERICA By

John M. Fogg, Jr. Vice-Provost and Professor of Botany, University of Pennsylvania

Illustrations by Léonie Hagerty

UNIVERSITY OF PENNSYLVANIA PRESS Philadelphia

• 1945

Copyright 1945 UNIVERSITY OF PENNSYLVANIA PRESS Manufactured by Lancaster

in the United States Press, Inc., Lancaster,

of America Pennsylvania

London Humphrey Milford Oxford University Press

Published with aid of T H E MORRIS

ARBORETUM

University of Pennsylvania

FOREWORD Many a gardener has carefully nurtured a row of "Marigold" seedlings only to discover to his sorrow that they were young Ragweeds, or has cherished a batch of embryonic "Radishes" merely to have them turn into Lamb's Quarters. Indeed, the manner in which weeds frequently resemble garden species is exceeded only by their diabolical capacity for surviving where cultivated plants perish. This unconscious mimicry on the part of weeds is all the more annoying in that it exists principally in the early stages of development, at which time the young foliage or the general habit of growth furnishes the only means of identification. Yet this is the very season in which the elimination of undesirable plants can most readily be accomplished. Any gardener who once neglects his plots until their weeds become unmanageable will doubtless resolve never again to permit these pests to reach maturity. He will probably swear a solemn oath to rip them out next time while they are still helpless babes, or certainly before they can produce flowers and a whole new crop of seeds. But at this point a difficulty will arise which may prove insurmountable: Which are weedlings and which are seedlings? How can he be certain that those tiny plants marshaled in such a straight row just where he planted Turnips are in reality Pigweeds? Or know whether those rosettes of white, woolly leaves in the corner of the rockery belong to Mullein-pink or Cudweed? Of the several excellent books on weeds which have appeared in recent years (the titles of which are included in the Bibliography) none has placed major emphasis on the aspect of the intruder at the very stage when it must be recognized if it is to be easily or effectively controlled. It is hoped that the present volume will contribute toward a better understanding of the appearance and behavior of the weed in its juvenile condition, especially when there is a significant difference between its early foliage and that of the mature specimen. T h e artist has in many cases included a drawing of the young plant or of the winter rosette, if such is regarded as helpful in establishing the identity of the species. In some cases, of course, this is unnecessary because the young individual is merely a replica in miniature of the adult. Grasses, for example, can usually be identified with certainty only when they produce their flowers, and little or nothing is gained by illustrating them in the seedling stage. Or, again, young plants of Carpet Weed, Purslane, Moneywort, and many others so closely resemble the later stages in everything except size that they can be recognized without fail from the time they first claim attention. In many species, however, the early or rosette leaves are so unlike the later foliage that persons who are thoroughly familiar with the mature plants are totally unable to recognize them in the young or dormant conv

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WEEDS O F L A W N AND G A R D E N

dition. Examples of this will be seen in such species as Shepherd's Purse, Henbit, Motherwort, Moth Mullein, and Great Ragweed. It is therefore desirable that those who work with plants should attempt to become familiar with the appearance of a given species in all phases of its development. Certainly the gardener who learns to distinguish weeds from cultivated plants, especially at that stage when they are most likely to be confused, will greatly improve his chances of being able to eradicate them before they cause irreparable harm. During the last few decades there has been a spectacular increase of interest in gardening which has embraced all classes of ornamentals: annuals, perennials, shrubs, and special-purpose plants such as herbs, bulbs, and rock-garden species. T h e more recent years have witnessed a tremendous development in small-scale vegetable growing, in both home and community gardens. All this has served to focus greater attention upon that category of plants generally known as "weeds. T h e professional botanist is now, more than ever, besieged with requests to identify, usually from a verbal description or a fragmentary specimen, this or that unwelcome intruder in the garden. This request is almost invariably followed by the query, "How can I get rid of it?" I t is therefore with the hope of enabling the gardener to identify the most common weeds of lawn and garden that this volume is prepared. It may also be that some of its hints concerning extermination will prove useful. But it should be borne in mind that in the matter of weed control, especially in the average-sized garden, there is no panacea, few short cuts, and no real substitute for just plain weeding. T o my friend Dr. William J . Phillips I am indebted for providing the stimulus that crystallized an intention of several years' standing to prepare such a book. Mrs. A. C. Barnes, Miss Lillian Hensleigh, and Dr. Thomas S. Githens have kindly contributed the living specimens used for several of the drawings. Dr. H. C. Barker, Dr. Sculley Bradley, and Dr. H. S. Lukens, of the University of Pennsylvania faculty, have all made helpful suggestions. My colleagues in the Department of Botany, Dr. J . R . Schramm, Dr. E. T . Wherry, Dr. Conway Zirkle, and Mr. Robert L. Schaeffer, Jr., have given freely of their time when consulted on a variety of matters, and Mr. Bayard Long, of the Philadelphia Academy of Natural Sciences, has brought his keen judgment to bear on several questions submitted for his consideration. T o these, as well as to many others who have encouraged this work, my deepest thanks are due. Most of all am I grateful to my wife, who has read manuscript and proof, and by her unflagging interest and advice has made the preparation of this volume not only a possible but a pleasant undertaking. J . M. F. Philadelphia January 1945

CONTENTS Page v

FOREWORD INTRODUCTION What is a Weed? Why some Plants are Weeds T h e Dispersal of Weeds T h e Geographic Origin of Weeds T h e Extermination of Weeds Chemical Controls Weeds as Soil Indicators

1 1 4 8 10 17 20 23

ILLUSTRATIONS AND DESCRIPTIONS OF WEEDS

25

T R E E WEEDS

199

GLOSSARY

202

BIBLIOGRAPHY

206

INDEX

207

vii

INTRODUCTION WHAT IS A WEED? * Of the various definitions of the term "weed" which have been advanced— and they have been numerous—perhaps none is more widely accepted than that which holds that a weed is "any plant which grows where it is not wanted." This, of course, implies that something else is wanted, and suggests that a knowledge of what that something else is will aid in determining just which plants are to be considered weeds. For example, the sentiments with which the farmer, interested in forage or grain, will view Timothy, Alfalfa, Clover, or Oats will differ radically from those entertained toward them by persons whose lawns, gardens, and truck patches they invade. Conversely, Ox-eye Daisy and Black-eyed Susan, which are regarded with affection by many, will be branded by the farmer as unmitigated nuisances. Dandelion, Lamb's Quarters, and Pokeweed are highly valued for the "greens" they provide, but their appearance in lawn or garden is cause for lamentation. Bouncing Bet and Butter-and-eggs may elicit admiration when growing in colorful masses along railroad or highway, but no self-respecting gardener wants them on his premises. Even certain plants which have been intentionally introduced into the garden, because of their beauty or some other desirable quality, have manifested a disposition to get out of hand and have worn out their welcome. They, too, must be designated as weeds. Combined with their genius for growing "where they are not wanted," most plants which are characterized as weeds possess to an unusual degree a joint capacity for vigorous growth and survival under adverse conditions. One need only examine a garden during a drought to be aware of this fact: Corn has wilted, Beans are gasping for water, the familiar ornamentals wear a bedraggled look, but Purslane, Carpet Weed, Dock, and the rest of the weedy tribe appear to be thriving! It is worthy of note that a given species may be a weed in one locality or under one set of conditions, yet behave as a perfectly innocuous plant in another. Thus Wild Carrot and Ox-eye Daisy, which seldom occur profusely in their native European haunts, may take possession of entire fields in this country. The reasons underlying this disparity may have to do with differences in soil and climate or, in many instances, with the competition offered by other plants. The criteria which lead to certain plants being classed as weeds are derived from a knowledge of their occurrence and behavior rather than because of their lack of beauty. Indeed, many species universally out* See

GLOSSARY,

page 202, for definition o£ terras. 1

2

WEEDS O F LAWN AND GARDEN

lawed as weeds are extremely attractive and, were it not for their inherent tendency to dominate any situation into which they are projected, might rank high in popular favor. Sulfur Cinquefoil, Flower-of-an-hour, Blueweed, Butter-and-eggs, Orange Hawkweed, to name only a few, are all plants which possess showy or interesting flowers; they might be considered pets instead of pests if only they could practise self-restraint. On the other hand, such familiar weeds as Pigweed, Wormwood, Horseweed, Tumbleweed, Knawel, Carpet Weed, and a host of others are anything but lovely, and would doubtless be excluded from polite society even were their manners unimpeachable. Still others, such as Jimson Weed and Horse Nettle, are on the blacklist because their coarse scent or sharp spines render them disagreeable or dangerous. Many species are condemned as weeds not so much for their intrinsic ugliness as for their aggressive tendencies, their predilection for waste ground, and the persistence with which they resist eradication from areas which have been" allocated to other and more desirable plants. Weeds belong to no special group or family of plants, although it is of interest to note that certain families like the Grasses and the Composites, which the botanist considers of relatively modern origin, have contributed a significantly large number of weed species. Youth, even in the evolutionary sense, seems to imply aggressiveness, vigor, and pioneering ability. Nor have weeds any uniform habit or manner of growth. Many are annuals, some are biennials, a large number are perennials. Some are low-growing or prostrate, others are upright and branching, still others are climbing or twining plants. Even a few trees must be counted as weeds: Ailanthus, Black Locust, and Silver Poplar, for example, may prove as obnoxious in the garden as Pokeweed, Ground Cherry, or Nightshade. It should be emphasized that the concept of a weed herein developed is applied in a somewhat restricted sense. Certain plants which occur abundantly in vast agricultural sections of the country seldom find their way into small gardens or lawns, and are therefore excluded from this work. Many other species which are members of our native flora grow in such profusion in meadows, fields, or marshland that they are often designated as weeds by the botanist, yet they seldom stray into cultivated ground. T o this group belong the Goldenrods, Asters, Ironweeds, Bonesets, Sunflowers, and many more. On the other hand, it has seemed advisable to admit to this volume several species which normally flourish in cleared land, vacant lots, or abandoned fields. T h e increasing conversion of such habitats to the growing of vegetables means that certain plants not usually considered garden weeds are now making their appearance in the truck patch. This group includes Timothy, Orchard Grass, Purple T o p , Foxtail Grass, Brome Grass, Hedge, Mustard, Winter Cress, Rough Cinquefoil, St. Johnswort, Milkweed, Thistle, etc. Many other plants are candidates for ad-

WHAT IS A WEED?

3

mission on this basis, and probably no two individuals will agree on a selection, but the distinction which is attempted here has been based on the tendencies which such plants are believed to possess for perpetuating themselves in cultivated ground. Another distinction, and one which cannot always be maintained, is that which exists between cultivated species which are definitely weeds within the boundaries of the garden and those which, not satisfied with the space allotted to them, have transgressed the barriers of domestication and have naturalized themselves in the countryside at large or have invaded other gardens. Examples may be drawn from the three main classes of garden plants: annuals, biennials, and perennials. A number of annuals such as Larkspur, Spider-flower, Petunia, and Cosmos tend to perpetuate themselves year after year by seed, and their progeny may even be so numerous that they are treated as weeds and pulled up to make room for more desirable species. These plants, however, show little or no disposition to escape as widespread weeds and are therefore not treated in the main body of this work. Quite different, however, is the case of Snow-on-the-mountain, which is not only a pest in the garden but has become a conspicuous weed of roadsides and waste places throughout wide areas. In the biennial group, Hollyhock is a good illustration of a plant which may be relied upon to seed itself successfully season after season, yet except for its occasional occurrence on a waste heap where garden refuse has been dumped, it is seldom found in a wild state. Indeed, a few biennials, such as Canterbury Bells and Foxglove, often fail to seed themselves in the garden and must be started anew each year to insure their presence in the border. On the other hand, a plant like Brown-eyed Susan, Rudbeckia triloba, is capable not only of dominating the garden plot but also of becoming a conspicuous weed in a variety of habitats, and is therefore treated in the pages which follow. By far the largest number of ambitious garden plants are perennials. Species like False Dragon-head, Physostegia, Bergamot, Monarda, White Loose-strife, Lysimachia clethroides, Mistflower, Eupatorium coelestinum, Chinese Lantern Plant, Physails Alkekengi, and Golden Glow, Rudbeckia laciniata, var. hortensia, to mention only a few, are so arrogant that many gardeners have long ago elected to exclude them altogether. Yet, despite the strong persistent root systems which enable them to spread rapidly, none of the species mentioned tends to stray very far from those gardens which still admit them. On the contrary, such plants as Moneywort, Lysimachia Nummularia, Cypress Spurge, Euphorbia Cyparissias, and Tickseed, Coreopsis lanceolata, are not only "space-bags" in the garden, but have infiltrated the native vegetation to such extent that they must be included in any volume devoted to weeds. Finally, mention should be made of a group of plants which, though once widely cultivated, are no longer seen in gardens. A few of these,

4

WEEDS O F LAWN AND G A R D E N

such as Butter-and-eggs, Linaria vulgaris, and Soapwort, Saponaria officinalis, are now of country-wide occurrence. I t will be noted that the examples above cited are all drawn from the flower garden. T h i s does not imply that the inhabitants of the vegetable garden are free from the taint of weediness. It is true, however, that the familiar representatives of the truck patch are distinctly in the minority in this regard. Peas, Beans, Tomatoes, Corn, Cabbage, Lettuce, Beets, and many other table-plants are widely grown, and yet probably not one of them occurs in the wild except as a casual waif and then usually in the vicinity of waste heaps or public dumps. An exception may be seen in the case of W i l d Carrot, but there is reason to doubt whether this plant as we see it growing wild is directly derived from the garden. It seems more reasonable to believe that it owes its presence in our spontaneous flora to an independent and early origin from stock which was long ago differentiated from the cultivated form. T h e answer, then, to the question " W h a t is a weed?" is not a simple one, but will vary according to the locality, the association with other plants, and the horticultural objective or point of view of the individual gardener. Certain plants considered weeds by some may have been omitted from these pages, others not generally so regarded may have been included. T h e intention has been not to offer a comprehensive treatment of the subject, but rather to introduce to the gardener the more familiar representatives of a group of plants, an acquaintance with which may enable him to combat their activities. W H Y SOME PLANTS ARE WEEDS As has been indicated, the answer to the question as to what constitutes a weed is not an easy one. Still more difficult is it to determine just what are those factors which enable certain plants to function as weeds, usually at the expense of their less gifted competitors. T h e question really is, " W h a t are the inherent attributes of weediness, and are they the same for all species?" Merely to say that some plants are weeds because they are endowed with the power of vigorous growth or possess a prodigious capacity for reproducing themselves, is to offer a partial and somewhat evasive answer. Yet possibly, in view of the present state of our knowledge, this is the best answer that can be formulated. I t will be shown in a following section that many weeds are members of families which are considered to be of relatively recent evolutionary origin. Families such as the Grasses, the Mints, and the Composites are regarded as modern groups. Among the characteristics of youth which they exhibit (aside from those which have to do with flower structure) may be cited their ability to migrate, their adaptability to a wide variety of soil and climatic conditions, and their capacity for producing and disseminating their seeds. T o these families, and a few others also recog-

W H Y SOME P L A N T S A R E W E E D S

5

nized as of modern origin, belong an impressive number of weedy species. While there can be little doubt that a real relationship exists between youthfulness and weediness, acceptance of this fact merely raises additional questions, to which the answers are either very difficult or perhaps not yet available. Any real attempt to ascertain just what those characteristics are which result in some plants being weeds and others not, involves studies in such fields as physiology, ecology, soil chemistry, and microbiology. It deals with such considerations as whether the root-hairs of weeds are able to establish an osmotic turgor in excess of that of other plants, thus robbing them of available moisture in the soil; or whether weed species are capable of creating a higher root pressure which enables them to perform their functions more efficiently than other plants; or, again, whether they can utilize mineral nutrients or organic salts in a less reduced form than that required by other plants. Interesting though these problems may be to those technically qualified to deal with them, they lie outside the scope of the present volume. Moreover it may be noted in passing that answers even to the questions raised above are not always forthcoming, for as yet we know far too little about the actual mechanism by which a species or an individual responds to its environment. So we are forced back to the level of a superficial answer, and are compelled to explain the "whyness" of a weed in terms of its vigor, its resistance, its adaptability, and its productivity. Even on this superficial level, however, it is possible to indulge in certain useful generalizations concerning the quality of weediness. It may therefore be found profitable to examine the way of life of some characteristic weeds with a view to ascertaining whether they have anything in common. Underground system. Most weeds have extensive subterranean systems which not only anchor them firmly to the ground, but enable them to absorb from the soil large amounts of water with its dissolved mineral salts. In the case of annuals, such as Sudan Grass, Fall Panicum, Hemp, Lamb's Quarters, the Pigweeds, and Common Nightshade, the root system is generally of the kind termed fibrous, that is, it is composed of numerous vertical and lateral roots which may branch and re-branch many times, forming a dense mass of fine rootlets. Such a system not only robs other plants of their much-needed moisture, but may actually make it difficult for their underground parts to develop normally if at all. In biennials and perennials, although fibrous roots may be produced (especially in the early stages of growth), the underground system is modified for continuous growth and is therefore usually enlarged and thickened. Such plants commonly develop a tap root, that is, a single main axis which gives off a few lateral branches or secondary roots. T a p roots are well endowed for storage purposes and enable the plant to survive for

6

WEEDS OF LAWN AND GARDEN

two or more years. They are found in such species as Curly Dock, Bitter Dock, Pokeweed, White Campion, Black Medic, Evening Primrose, Wild Carrot, Wild Parsnip, Broad-leaved Plantain, Burdock, Chicory, and Dandelion. They may be either greatly thickened as in Pokeweed, or long and slender as in Dandelion. Some tap roots have been found which penetrated the soil to a depth of six or seven feet. Not all biennial or perennial plants produce tap roots. Some, like Sheep Sorrel, Live-forever, Cypress Spurge, Bindweed, and Butter-andeggs, possess roots which are only slightly enlarged for storage purposes, but may be tough and woody and able to creep extensively in a horizontal position. Many perennial weeds, in addition to having more or less permanent root systems, possess modified subterranean stems. When these underground stems are elongated and horizontal they are called rootstocks or rhizomes. In general, a rhizome differs from a true root in that it is capable of producing buds which develop into leaves or new stems. Rhizomes have nodes and internodes and may, as in the case of Quack Grass, be provided with scales or bracts. Examples of weeds which possess rhizomes are Quack Grass, Bermuda Grass, Johnson Grass, Nimblewill, Yellow Cress, Milkweed, Hedge Bindweed, Mugwort, Yarrow, and Canada Thistle. Other types of subterranean stems are the bulb, the corm and the tuber. A bulb is a shortened or disk-like stem from which arise numerous fleshy scales. Field Garlic is an example of a weed which produces bulbs. A corm, which is exemplified by Bulbous Buttercup, resembles a bulb but lacks the scales of which a bulb is composed. A tuber is an enlarged fleshy underground stem borne usually at the end of a rhizome. The most familiar example is the common white potato. Among weeds which produce tubers are Nut Sedge and Jerusalem Artichoke. The above observations must not be construed as applying only to weeds, to the exclusion of other groups of plants. It is, however, significant that so many weed species have, to such a marked degree, unusually well developed or highly modified underground parts. Stems and leaves. There is little or nothing in the aerial vegetative structures of weeds to differentiate them from other plants. It may be noted, however, that several weeds, such as Purslane and Live-forever, have succulent or fleshy parts which enable them to store moisture in times of drouth, and that the stems and leaves of certain others are densely clothed with pubescence, e.g., Blueweed, Gromwell, Common Mullein, Black-eyed Susan. Still other species, such as Horse Nettle, Canada Thistle, Bull Thistle, and Prickly Lettuce, are provided with formidable prickles or spines. It is also of interest to observe that a number of weeds have leafy runners or stolons which enable them to spread over the surface of the ground. Examples of this tendency are seen in Creeping Buttercup,

W H Y S O M E P L A N T S A R E WEEDS

7

Common Cinquefoil, St. Johns-wort, Yellow and Orange Hawkweeds, and Mouse-ear Hawkweed. T h e stolons of these and other species have the power of creeping out from the main stalk and taking root as they travel, ultimately forming new plants. A modification of this is seen in the case of species in which the entire stem system is a creeping rather than an upright one. Plants like Chickweed, Lawn Pennywort, Moneywort, and Ground Ivy, lead a prostrate existence, their stems trailing and rooting freely at the nodes. Another attribute of certain species is the "tumbleweed" habit, which enables plants to become detached from the ground and, by their lightness and the densely branching character of their stems, to be rolled or blown about by the wind, scattering their seeds as they go. Again it must be emphasized that the modifications enumerated above are by no means peculiar to weeds, but are interesting in that many weed species exhibit them to a significant degree. Flowers. T h e species treated in this volume, including the eight trees illustrated on pages 200 and 201, belong to no fewer than forty-five different families. As would be expected, therefore, weeds manifest considerable diversity in the color, form, and arrangement of their flowers. It is true, of course, that the flowers of many weeds, such as Hemp, Clearweed, Lamb's Quarters, Pigweed, Wormseed, Knawel, Spurge, Honewort, Mugwort, and Ragweed, are small and inconspicuous. Quite as many, on the other hand, have flowers which are large and showy, e.g., Sulfur Cinquefoil, St. Johns-wort, Flower-of-an-hour, Evening Primrose, Purple Fireweed, Coreopsis, and Black-eyed Susan, to mention only a few. T h e r e are, however, two general tendencies discernible in the flowers of weeds which are worthy of mention: one is the preponderance of windpollinated species; the other is the trend toward aggregation of flowers in a compact inflorescence. T o the group of wind-pollinated species belong the grasses (of which thirty are here illustrated, and several others mentioned in the text), the Docks, Lamb's Quarters, Pigweed, Wormseed, the Plantains, and, in the Composite Family, Cocklebur and the Ragweeds. This type of pollination is highly wasteful, for it involves the liberation of tremendous quantities of excess pollen, and it is probably no mere coincidence that windpollinated species frequently occur in such dense stands. It may be noted in passing that the pollens of some of the plants named above are among the most guilty»of all those accused of inducing "hay fever" symptoms. T h e aggregation of flowers into a compact or common inflorescence is as efficient a mechanism for insuring pollination as the previous method is crude, for it means that a single insect visit may accomplish a large number of acts of fertilization. This trend which is seen in the Clovers, some of the Parsley Family, and most of the Mints, reaches its culmination in the Composites. Here a great many flowers (in some genera several hundred) have been united in a common head, which may even be surrounded

8

W E E D S O F L A W N AND G A R D E N

by a row of modified florets which increases its showiness. I t is therefore highly significant to remark that the Composite Family is the largest, the most successful and, in many respects, the most modern and aggressive of all plant families. T h i s is clearly reflected in its weedy representatives. Thirty-seven members of this family are illustrated and a goodly number of others mentioned, making it, even from the point of view of numbers alone, the most important weed family. Fruit and seed. Many and interesting are the devices which may be seen in the fruit and seeds of weed species and help to insure their perpetuation and spread. Since, however, they are more directly related to the subject of dispersal, to be treated in the following section, no discussion of them is needed here. T h e above observations, many of which apply equally well to plants other than weeds, probably bring us no closer than we were at the outset to a comprehension of the fundamental qualities of weediness; they should, however, help to establish a composite picture of the superficial attributes of a class of plants which have been eminently successful in making their own way in the world. T H E DISPERSAL OF WEEDS Although weeds generally possess vigorous roots or underground stems which often enable them to form extensive colonies, the primary functions of the subterranean system are anchorage and absorption, and they are not designed to aid the plant in traveling from place to place. An exception to this statement may be seen in cases where basal systems, after being dug up, are carelessly discarded or transported to waste ground. Here, thanks to their amazing vitality, roots, rhizomes, bulbs, etc., may be capable of initiating new colonies. Miss A. E. Georgia reports an Indiana farmer as stating that the rootstocks of Horse Nettle retained their vitality for ten years under a heap of sawdust. Mention has already been made of the tumbleweed habit, whereby the entire plant becomes detached and is carried or rolled by the wind often for considerable distances, scattering its seeds over a wide area. T h e dispersal of plants by means of their vegetative parts is, however, highly exceptional, the overwhelming majority of species being transported almost solely by their fruit and seed. T h e subject of plant dissemination is an exhaustive one, and all that will be attempted here is a brief account of a few of its basic principles in so far as they apply to weeds. First of all it must be understood that the botanist uses the term " f r u i t " in referring to the matured ovary, with its contained seed or seeds, whether that body be fleshy or dry. T h e hard, one-seeded grain of the grass and the achene of the Smartweed are just as truly fruits as are grape, cherry, and banana. T h e capsule and the legume (both of them loosely termed "pods") are also true fruits, but ones which differ from the grain and achcne in that they split open at maturity liberating their seeds.

T H E DISPERSAL O F WEEDS

9

Both seeds and fruits exhibit a wide variety of adaptations fitting them for dispersal by means of a number of agencies, chief among which are water, wind, and animals, including man. Water. A number of weeds, such as Peppergrass and Plantain, develop seeds with mucilaginous coverings which enable them to be immersed in water without injuring the embryo. Such seeds may either be transported by streams and rivers or, at times of flood or heavy rainfall, be carried across wide areas or transported from one section of the lawn to another. Other seeds, such as those of members of the Mustard and Parsley families, are buoyant and can be floated for a considerable length of time and over great distances by water currents. Wind. Wind is probably the most important instrumentality through which plants are disseminated, and the adaptations exhibited by their fruits and seeds in this regard are numerous and varied. Some fruits are provided with winged appendages which fit them for traveling by air. Examples of these are the samaras, or key fruits of Maples and the Ailanthus. Any garden or lawn in the vicinity of Norway Maples will be bombarded by these fruits, and pains should be taken in late fall or early spring to see that they are completely raked u p ; the alternative is an endless succession of small maple seedlings, of the type shown on page Most wind-dispersed fruits, however, depend upon a row or series of bristles or fine hairs attached usually at one end. T h e outstanding family in this respect is, of course, the Compositae, with Dandelion, Hawkweed, Lettuce, Thistle, Sow Thistle, Cat's-ear, Oyster Plant, and many others as examples. T h e fruit in all these cases is a modified achene, which is provided with a "parachute" of fine hairs (the pappus). T h e efficient use which this family makes of the wind as a transporting agency is well attested by the widespread distribution of many of its species. In the case of these Composite genera which are weeds, the heads should be removed while still in flower, if not earlier, and should be destroyed by burning or other means. Since these flowers are capable of maturing their achenes, even when detached from the plant, there is nothing to be gained by merely cutting off the heads and dropping them on the ground or throwing them on the compost heap. Seeds, as well as fruits, may be endowed with hairs or bristles which fit them for aerial transportation. T w o of the best examples are the seeds of Purple Fireweed and Milkweed. T h e hairs in these instances represent a modification of the outer seed-coat. Animals. Here, again, as is true of wind-dispersed plants, both fruits and seeds exhibit devices which fit them for dispersal by means of animals. T h e role played by fleshy fruits is a familiar one. T h e seeds of such fruits are usually able to pass unharmed through the digestive tracts of birds or other animals, and may in this way be deposited at great distances from the parent plant. Pokeweed and Nightshade are examples of weeds which are distributed in this manner.

10

WEEDS O F L A W N A N D G A R D E N

O t h e r fruits are provided with hooks, barbs, awns, or spines, which enable them to adhere to the coats of animals or the clothing of man. Such adaptations are seen in the grains of a few of the Grasses (e.g., Sandbur), the f r u i t of some of the Parsleys (e.g., Wild Carrot), the bristly twin-fruit of the Bedstraw, but, above all, in the Composite Family, where such forms as Spanish Needles, Beggar Ticks, Burdock, a n d Cocklebur furnish excellent illustrations. Even a few seeds, such as those of Clover, are adapted for dispersal by animals, although here again, as in the wind-borne forms, it is far more customary to find that it is the fruit-coat, rather t h a n the seed-coat, which has u n d e r g o n e modification. T h e p a r t which m a n has performed, both in o p e n i n g u p the country a n d in transporting plants, either intentionally or inadvertently, f r o m faroff places is a tremendous o n e a n d will be dealt with in the section o n Geographic Origin of Weeds. It remains merely to p o i n t out that certain species depend u p o n n o n e of the agencies here listed, b u t have developed scattering devices of their own. T h e capsules of the Violet, for example, open explosively, projecting their seeds to a distance of several inches. T h e carpels of the Cranesbill, when mature, snap violently upward, h u r t l i n g their seeds over a n area of several square feet. I n these, a n d many other ways, weeds contrive to scatter their reproductive bodies as far as possible f r o m the p a r e n t plant. In large measure, then, the wide distribution which many weeds enjoy is d u e to the efficiency of their methods of dispersal. THE GEOGRAPHIC ORIGIN OF WEEDS Analysis of the geographic origins of the 242 weeds either illustrated or given particular m e n t i o n in the text accompanying the illustrations reveals the following information: 128 species (approximately 53%) are of European or Eurasian origin; 78 species (32i/ 2 %) are native to N o r t h America (although some of them occur in the O l d W o r l d as well); 21 species (approximately 8%) come f r o m eastern Asia or India; 13 species (5i/2%) are indigenous to the tropical or subtropical portions of America, a n d 2 species (less than 1%) are derived f r o m Africa. As will be observed, the E u r o p e a n a n d Eurasian immigrants (53%) o u t n u m b e r the combined representatives f r o m all other parts of the world, including the native American species. T h e reasons underlying this preponderance of European species are worthy of consideration. First of all, it will be realized that since the N e w W o r l d was settled by colonists f r o m Europe it is only reasonable to find here a large proportion of species f r o m that continent, especially the western half. N o t all these so-called European species, however, are restricted to western Europe; some of them occur in the eastern Mediterranean, in Asia Minor, and in western or southwestern Asia. It is for that reason that they are

T H E G E O G R A P H I C O R I G I N O F WEEDS

11

designated as Eurasian. Probably many more are actually of central or western Asiatic origin (as distinct from the Far East) but have been grown in Europe for so many centuries that they appear indigenous there. As might be expected, the early colonists brought with them many species of European origin, some as ornamentals, some as vegetables, others as forage or pasture plants, still others as potherbs, medicináis, or condiments. Many of these plants have escaped from cultivation and are widespread weeds today. Still larger numbers of European species have reached these shores as stowaways either in the rigging or ballast of ships, as impurities in consignments of grain and fodder, included among packing materials or attached to garden implements or countless other objects. Ship's ballast has constituted one of the most prolific sources of introduction, for in early days vessels sailing light carried as ballast tons of dirt which was shoveled overboard upon making port. This eartli naturally contained the seeds of numerous foreign plants, and many and interesting were the exotic species which botanists of a century or more ago found flourishing along the wharves of the Atlantic seaboard. Some of these plants, alien to our climate, perished after a season or two; many more have persisted to become our most obnoxious pests. A goodly number of them are included among the 128 European species here treated, but it should be emphasized that several hundred more are present in our flora, although they may not be sufficiently abundant to be considered as common or troublesome weeds. In addition to the historical reasons which help to explain the presence of such a large percentage of European plants in our country, there are certain geologic and climatic factors which should be taken into account. Within comparatively recent millions of years, the continent of Europe and portions of Asia have been subjected to various influences which have tended to destroy or modify the existing vegetation, not once but several times. One of these was inundation or drowning, which affected much of southern Europe and Asia Minor. (At one time the Mediterranean Sea covered almost three times the area which its present basin occupies.) Another factor has been the elevation of certain mountain ranges with accompanying changes in temperature-moisture relationships. T h e most recent destructive force has been that of glaciation—the accumulation of great ice sheets which have completely wiped out the vegetation of much of western Europe. As a result of these combined factors, a large proportion of the original forest flora of Europe has been destroyed and has been replaced by vegetation which is of recent origin—recent not only as to length of occupation of a given area, but recent also in that it is composed largely of families which are modern in the evolutionary scale. Since a modern or youthful flora is almost invariably endowed with the attributes of aggressiveness and migrating ability, it becomes possible to understand why, when these plants were transported across the Atlantic, they proved so successful in

12

WEEDS OF LAWN AND GARDEN

their conquest of a new continent, especially its eastern portion. Many European animals (e.g., the "English" sparrow and the starling) have behaved in similar fashion, and man's own activities offer an interesting parallel. Indeed, the part which man has played in opening up this new world has had a profound influence on the spread of weeds, not alone the European species, but those from other parts of the globe as well as certain native plants with weedy tendencies. When white man reached this country over four and a half centuries ago, he found its eastern half occupied by a well-established forest flora. From Pennsylvania southward these forests were composed mainly of hardwood or deciduous species, and constituted a climax formation representing the biological equilibrium achieved through millions of years of adjustment to relatively stable geologic and climatic conditions. In New York, New England, and Canada, the original flora had been destroyed by glaciation (just as had been the case in Europe) and the present-day flora of that area is the result of revegetation dating from the disappearance of the last great ice sheet, some thirty thousand years ago. But the fact remains that the early settlers found the eastern portion of North America dominated by a very dense and relatively stable forest flora. It is interesting to speculate on just what success these weeds from Europe would have had in competition with this well-established woodland vegetation, had the way not been made easy for them. Without human aid most of them would never have reached this continent. Without the transformation wrought by human activities, they might never have been given an opportunity to survive or spread. As it is, man has cut down or burned the forests, ploughed the land, built cities, railroads, and highways, altered the natural drainage; in short, he has modified the face of nature in every conceivable manner. T h e result is that these European adventives, instead of having to compete against a firmly entrenched and undisturbed native vegetation, have, thanks to their pioneering vigor, been able to take advantage of such artificial habitats as farms, pastures, roadsides, waste places, vacant lots, lawns, and gardens. A list of the more important weeds of European origin follows. Those marked with an asterisk occur also in Asia. N. B.

(In the case of this and other enumerations of species here presented, the plants are listed in family order and their sequence corresponds to that followed in the descriptive portion of this work. See page 26.)

* Quack Grass *Redtop Sweet Vernal Grass Oats Hairy Chess

Downy Chess Orchard Grass Hairy Crabgrass Smooth Crabgrass • Barnyard Grass

T H E G E O G R A P H I C O R I G I N OF WEEDS Stink Grass Velvet Grass Rye Grass •Timothy Low Spear Grass Canada Blue Grass Yellow Foxtail Green Foxtail Bur Foxtail Slender Rush Field Garlic Lady's T h u m b Black Bindweed Sheep Sorrel Curly Dock Bitter Dock Lamb's Quarters Knawel *Corn Cockle Common Chickweed Mouse-ear Chickweed White Campion Night-flowering Catchfly Bouncing Bet Purslane Bulbous Buttercup Tall Buttercup Celandine Scurvy Grass Rutabaga Shepherd's Purse Whitlow Grass Mouse-ear Cress Field Peppergrass Wild Radish Yellow Cress T u m b l e Mustard Hedge Mustard Penny Cress Live-forever Sulfur Cinquefoil •Black Medic Rabbit-foot Clover Purple Clover Alsike Clover Yellow Hop Clover

* Hairy Vetch Yellow Wood-sorrel Cypress Spurge Flower-of-an-hour Common Mallow Musk Mallow Common St. Johns-wort Wild Carrot Wild Parsnip Scarlet Pimpernel Moneywort Bindweed Blueweed Gromwell Hemp Nettle Henbit Red Dead-nettle Motherwort Catnip Ground Ivy Climbing Nightshade *Butter-and-eggs "Common Mullein *Moth Mullein Broad-leaved Plantain Buckhorn Mayweed Burdock Star Thistle Cornflower Ox-eye Daisy Chicory •Canada Thistle *Bull Thistle King Devil Devil's Paintbrush Mouse-ear Hawkweed Cat's-ear Prickly Lettuce Groundsel Sow Thistle Tansy Common Dandelion Red-seeded Dandelion Oyster Plant Salsify

14

WEEDS O F L A W N AND G A R D E N

Of the 78 species (32i/2%) of American origin it is interesting to observe that 66 are apparently indigenous to the eastern portion of the continent, where they were supposedly components of the primeval flora, and 12 are native to areas west of the Mississippi River, whence they have migrated eastward in historical times. Taking first those species common to the eastern states, it may be noted that whereas a few of them, like Clearweed, Three-seeded Mercury, Poison Ivy, and Honewort, are primarily plants of the woodland, the great majority are species of exposed dry or moist habitats. Even though the Appalachian Plateau was densely covered with an almost impenetrable forest in early times, there must always have existed open marshy situations or exposed shale, serpentine, or limestone barrens or essentially treeless mountain summits to provide habitats for these light-loving species. I t seems reasonable to suppose that a plant such as Evening Primrose was at one time restricted to such situations, but that, with the clearing of the land, it has become of country-wide occurrence. T h e question naturally arises why many more native species have not taken advantage of the opening up of the country to spread in a manner similar to that of the European introductions. T h e answer to this query has already been indicated by the reference made to the comparative ages of the two floras. Whereas the flora of that part of Europe from which most weed-species have come consists largely of modern and aggressive groups of plants, the original woodlands of eastern America were composed of an assemblage of plants belonging to relatively primitive families. T h e very antiquity of these families, added to the fact that in this region they have occupied the same ground for so long a time, means that their species have become intimately adjusted to a uniform set of conditions. This very adjustment has resulted in these plants becoming conservative and lacking the ability to meet new and changing conditions such as may be created by the clearing and plowing of the land. In the main, therefore, our native eastern woodland species have been much slower to take advantage of newly available ground than the less finely adjusted and therefore more aggressive plants from certain other parts of the world. T h e following list includes the more familiar eastern American species which occur as weeds in our area. Those marked with an asterisk are apparently native also to Europe or Asia or both. Sandbur Purple Lovegrass Nimblewill Fall Panicum Deer-tongue Grass 'Kentucky Blue Grass Purple T o p Nut Sedge Clearweed

'Common Knotweed 'Pennsylvania Smartweed Pale Smartweed *Water Smartweed *Water Pepper Pokeweed Sleepy Catchfly Peppergrass ' R o u g h Cinquefoil

T H E G E O G R A P H I C O R I G I N O F WEEDS Common Cinquefoil Carolina Cranesbill Three-seeded Mercury Creeping Spurge Nodding Spurge Poison Ivy Clammy Cuphea Purple Fireweed Evening Primrose Honewort Milkweed •Hedge Bindweed White Vervain •Self-heal *YVild Basil Ground Cherry Horse Nettle •Common Nightshade

15

•Common Speedwell •Purslane Speedwell Thyme-leaved Speedwell Rugel's Plantain Cleavers Venus' Looking Glass Indian Tobacco •Yarrow Spanish Needles White Fireweed Daisy Fleabane Horseweed White Snakeroot Common Everlasting •Pearly Everlasting Jerusalem Artichoke Wild Lettuce

T h e dozen or so western American species on the weed list offer an interesting comparison with the above group. Coming mainly from the plains and prairies of the West and Middle West, these plants belong primarily to families which are of modern origin and lack the continuity of occupation seen in the case of the Appalachian woodlands. They thus have more in common with the plants of the Mediterranean area than with those of eastern North America. When introduced eastward, where they lack the active competition of other aggressive western species, they frequently spread rapidly and become dominant weeds. This group includes such plants as Winter Cress, Tumbleweed, Wormwood, and Ragweed. In marked contrast to the behavior of the European introductions is that of the 21 species (8%) which have been derived from the Orient and have become weeds in our area. Large areas in eastern and southeastern Asia have had a geologic history comparable to that of eastern North America. Free from destructive influences such as inundation, climatic alteration, and glaciation, this region has been able to retain much of its original vegetation for many millions of years. T h e story has been one of continuity rather than change, so that today eastern Asia has many of the same families and genera that occur in our eastern forests. Oriental species are thus essentially adapted to woodland conditions and, when introduced into eastern North America, accommodate themselves rapidly to woods and thickets rather than open fields, meadows, pastures, and other exposed situations. Asiatic plants, therefore, are better adapted for competing with our woodland flora than are the European adventives. In fact, some of them, like Japanese Hop, Japanese Knotweed, Japanese Honeysuckle, Ailanthus, and Empress Tree, are too well adapted for com-

16

W E E D S O F L A W N AND G A R D E N

fort and in many localities threaten to crowd out the native vegetation. Although the affinity which exists between the native flora of eastern temperate North America and that of southeastern Asia has been understood for nearly two centuries, Mr. Bayard Long seems to have been the first to point out that the ability of certain Asiatic species to adjust themselves to woodland habitats has brought them into direct competition with our native vegetation and has enabled them to become a conspicuous element of the flora in such situations. 1 T w o of the species which Long mentions, namely Wineberry, Rubus phoenicolasius, and Japanese Pampas Grass, Miscanthus sinensis, are not included in the present enumeration because, although locally abundant, their distribution is still regarded as somewhat restricted. Since Long's article was written, several additional species from eastern Asia have made their advent in the eastern states and are now either widely distributed or are in the process of becoming so. O n e is a species of Foxtail Grass, Setaria Faberii, which has only recently been recognized, but has now become dominant in many localities. Another is the Lawn Pennywort, Hydrocotyle rotundifolia, which has invaded shaded lawns in the vicinity of a number of our eastern cities. A third is a species of Asiatic Smartweed, Polygonum longisetum, which has taken possession of woods, thickets, roadsides, and even vacant lots in a manner which has been little short of phenomenal. T h e presence in our eastern flora of a small group of weeds from the warmer parts of America is indeed interesting. Such species as Wormseed, the Pigweeds, the Morning Glories, and Galinsoga are indigenous to the tropics or sub-tropics of Central and South America or the Caribbean. Many of these plants are annuals and, although unable to winter over, perpetuate themselves by means of seeds. If it is true, as some believe, that our climate is still recovering from the effects of the last glaciation (i.e., that we are gradually moving into a post-glacial, or perhaps only another warm inter-glacial, period) we may expect to see, over a long period of years, an incursion of warm temperate species into the middle states. T h i s probably will not account for the presence of these weeds in our flora, for their introduction has been by artificial means and of very recent date, but it may help to explain what seems to be a definite migration northward on the part of many species indigenous to the southern states. It is perhaps strange that more species from Africa have not found their way into our area, for there are sections of that continent with climatic conditions similar to those of eastern temperate North America, and a goodly number of African ornamentals (mostly annuals) are grown in our gardens. Johnson Grass and Sudan Grass are the only two weed species noted, although Carpet Weed, which occurs in the tropics of the New World, is said also to be native to Africa. i B. Long. "Certain Species Becoming Well Established at Ashbourne and Elsewhere Near Philadelphia." Bartonia. No. 3: 22-25. Philadelphia, 1910.

THE EXTERMINATION

OF WEEDS

17

THE EXTERMINATION OF WEEDS Most of the methods of eradication and control discussed in standard works on weeds are applicable primarily to agricultural conditions. The recommendations for plowing, harrowing, disking, pasturing, turning hogs into the land, burning, crop rotation, or alteration of drainage are ones which can seldom be followed in the lawn or average-sized garden, to the interests of which the present volume is chiefly devoted. N o r can the use of the various chemical herbicides be extensively invoked, except w h e n the weeds to which they may be applied occur in relatively solid stands or as isolated specimens. So many lawn and garden weeds occur in proximity to valuable plants that it is difficult to treat them in the same m a n n e r that is effective when such plants grow on farm land. It is true that the use of a few chemicals and selective sprays may be recommended, especially for lawn weeds, and the more important of these will be discussed later. T h i s does not signify that the home owner need completely ignore all phases of chemical weed control, a few of which are distinctly h e l p f u l in combating the spread of undesirable plants in lawn and garden. It is necessary, however, frankly to face the fact that in effecting the extermination of weeds in flower gardens, shrubbery borders, truck patches, and lawns, cultivation and pulling, either by h a n d or with special tools, are by far the most practicable and satisfactory methods. In order to deal intelligently with a given weed it will be f o u n d helpful to possess some understanding concerning its mode of life. T o this end, therefore, a few words may be in order concerning the longevity of weeds, their habits of germination, and the vitality of their seeds. T h e knowledge whether a weed is an annual, winter annual, biennial, or perennial places in one's hands an important weapon with which to combat it at the most vulnerable stage in its life history. Since this type of information is included in the treatment of the individual species here illustrated, it is necessary at this point only to summarize it briefly. A n n u a l s are most rapid and aggressive growers, for their very existence depends u p o n their ability to produce flowers and seeds in a single season. Such plants as Hemp, Prince's Feather, Lamb's Quarters, Mexican T e a , Pigweed, Purslane, Shepherd's Purse, Flower-of-an-hour, Clammy Cuphea, M o r n i n g Glory, Jimson W e e d , G r o u n d Cherry, C o m m o n Nightshade, Indian Tobacco, the Ragweeds, Spanish Needles, Beggar's Ticks, W h i t e Fireweed, Horseweed, C o m m o n Everlasting, Sow Thistle, and Cocklebur, despite the large size and robust appearance they may attain, are merely annuals. K n o w i n g this, the gardener should make every reasonable effort to prevent them from flowering, even if this means concentrating upon them for a time at the expense of other long-lived weeds. T h e seeds of annuals usually lie dormant until the following spring, but there is a small group of species, k n o w n as winter annuals, the seeds of which are capable of germinating before the close of the growing season in which they are matured. In late summer or early autumn these

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WEEDS O F LAWN AND G A R D E N

plants generally form rosettes which are capable of surviving the winter season and are thus ready to resume active growth early the following year. Examples of winter annuals are furnished by such plants as Corn Cockle, Shepherd's Purse, Peppergrass, Hedge Mustard, Tumble Mustard, Black Medic, Henbit, Mayweed, and a number of others. T h e behavior of these plants will differ somewhat according to geographic location, and certain species which are annuals in the northern portion of our area function as winter annuals farther south. As an illustration of this may be cited the case of Henbit, Lamium amplexicaule, which is usually an annual in New England but in the vicinity of Philadelphia germinates its seeds in September and may continue active growth until early December. It then dies down, but is prepared to resume growth early the following spring or even during occasional warm spells in midwinter. There is thus a certain amount of good work which the gardener can perform late in the year or in early spring in preventing the development of plants in this category as well as those of the following group. Plants of the biennial class, as their name implies, require two years to achieve full maturity. T h e i r first season is devoted to vegetative activity, and these plants usually develop a vigorous root system, well stocked with reserve food, and a rosette of basal leaves. Utilizing this supply of potential energy, the plant is able during its second year of growth to produce a succession of flowers and seeds. Some familiar biennial weeds are Wild Carrot, Wild Parsnip, Blueweed, Common Mullein, Moth Mullein, Black-eyed Susan, Bull Thistle, Brown-eyed Susan, Burdock, Salsify, and Oyster Plant. Again, the knowledge that these plants are biennials should enable the gardener to focus his attention upon them at a time when they are most easily and effectively destroyed. Perennials present the most difficult problem because of the more or less permanent nature and deeply intrenched position of their underground systems. In addition to many of the grasses, sedges, and rushes, this group, to which a large number of our most troublesome weeds belong, includes the following species: Field Garlic Japanese Hop Common Knotweed Japanese Knotweed Sheep Sorrel Curly Dock Bitter Dock Pokeweed Mouse-ear Chickweed Bouncing Bet Bulbous Buttercup Tall Buttercup Yellow Cress

Live-forever Sulfur Cinquefoil Common Cinquefoil Purple Clover Alsike Clover Cypress Spurge Poison Ivy St. John's-wort Blue Violet Purple Fireweed Lawn Pennywort Milkweed Bindweed

THE EXTERMINATION OF WEEDS Hedge Bindweed Motherwort Catnip Ground Ivy Self-heal Climbing Nightshade Horse Nettle Butter-and-eggs Common Speedwell Rugel's Plantain Broad-leaved Plantain Buckhorn Plaintain Japanese Honeysuckle

19

Yarrow Ox-eye Daisy Chicory Canada Thistle White Snakeroot Jerusalem Artichoke King Devil Devil's Paint-brush Mouse-ear Hawkweed Cat's-ear Tansy Dandelion

In the case of many of these species mere pulling is not sufficient, for it is too likely to leave behind portions of the subterranean system which are capable of renewed growth. Pulling when the ground is very soft is better than no pulling at all, but as a group these plants should be completely dug up or hoed out. It is true that, with some of them, repeated cutting back of the tops will eventually cause the demise of the roots, but this procedure is more precarious and only slightly less laborious than actually digging out the bases. When such plants occur in solid masses, however, resort may be had to some of the chemical methods of extermination referred to later. A knowledge of the germinating habits of weeds will likewise prove helpful in attempting to control them. Weeds, like other species, differ widely in the ability of their seeds to grow into new plants. Although most seeds require a winter resting period before being able to germinate, others can produce new individuals during the same season in which they are matured. This is, of course, true of most winter annuals. An extreme example of this tendency is seen in the case of Galinsoga, which is capable of producing several generations within a single growing season. Seeds of this species planted in mid-September in the latitude of Philadelphia have grown to maturity before frost and have continued to flower and liberate additional seeds until early in December. On thè other hand, seeds of Snow-on-the-mountain and Flower-of-anhour, sown in the same locality in August and September, have failed to germinate the same year, showing that they required a definite resting period. Some seeds must be planted within a year or two after they are matured; others are capable of retaining their capacity to germinate for relatively long periods of time. Muenscher states that it is not uncommon for weed seeds to retain their germinating power (viability) for ten, twenty, or even forty years, after having been buried in the soil (p. 5). As examples of seeds with amazing longevity may be cited:

20 Common Knotweed Black Bindweed Lamb's Quarters Rough Pigweed Knawel Common Chickweed Purslane Shepherd's Purse Rabbit-foot Clover

WEEDS O F LAWN AND G A R D E N Velvet L e a f Flower-of-an-hour Gromwell W h i t e Vervain Henbit Buckhorn Plantain Canada T h i s t l e Common Ragweed Ox-eye Daisy

I t will be obvious, then, that once the land has been cleared of these species, there is no guarantee that they will not continue to appear in succeeding seasons. O n e of the most troublesome of the lot is Purslane, whose seeds are such a frequent impurity among other seeds. T h e seeds of this species have been shown to retain their viability for thirty years. Small wonder that this plant reappears year after year in the same spot, even though the utmost care is taken to prevent individuals from reaching maturity. T o summarize, then: All classes of weeds must b e prevented from flowering; annuals should be pulled up or hoed out as soon as recognized; winter annuals and biennials can best be controlled by uprooting them in the rosette stage; perennials must be either severely and repeatedly cut back or completely dug out (preferably the latter); and recognition should be made of the fact that, despite the keenest vigilance and finest care, some weeds will continue to put in their appearance for a varying number of years. Despite all this, however, the battle is far from being of necessity a losing one, and the goal is distinctly worth the effort involved. C H E M I C A L CONTROLS T h e r e are listed and briefly characterized below some of the chemical weed-killers or herbicides, most of which have demonstrated their usefulness in experiments conducted over a long period of years. T h e gardener will do well to note their limitations as well as the warnings issued in the case of a n u m b e r of them. Wisely administered, they supplement but do not supplant the physical labor which is requisite for the creation of fine lawns and beautiful or useful gardens. Ammonium sulfamate. T h e use of Ammonium sulfamate as a weedkiller has been the subject of comparatively recent experimentation, but already the results obtained indicate considerable promise. In concentration of three-quarters of a pound of the chemical to o n e gallon of water, this solution applied to the leaves of Poison Ivy, Barberry, Wild Cherry, and a n u m b e r of other species has proved most effective. Grasses are apparently not seriously affected. I n the case of Poison Ivy several applications per season may be necessary, but the compound is regarded as

CHEMICAL

CONTROLS

21

s u p e r i o r to S o d i u m c h l o r a t e a n d totally lacks t h e fire-hazard p r o p e r t i e s w h i c h r e n d e r chlorates d a n g e r o u s to h a n d l e . I n t h e p r o p r i e t a r y f o r m in w h i c h A m m o n i u m s u l f a m a t e is n o w offered, it m a y b e used e i t h e r as a spray o r a p p l i e d in t h e dry c o n d i t i o n . 1 Ammonium sulfate. As utilized in h o r t i c u l t u r e , A m m o n i u m s u l f a t e is a d u a l - p u r p o s e c o m p o u n d : it is b o t h a fertilizer a n d a w e e d killer. W h e n e m p l o y e d as a n h e r b i c i d e , o n e p o u n d s h o u l d b e dissolved in two gallons of w a t e r a n d a p p l i e d as a spray. I n m o r e d i l u t e s o l u t i o n s it is beneficial to t h e l a w n , since it s u p p l i e s m u c h - n e e d e d n i t r o g e n . T h i s c o m p o u n d m a y also b e used in t h e dry c o n d i t i o n , six p o u n d s b e i n g d u s t e d over a n a r e a of a t h o u s a n d s q u a r e feet. I t is effective against C h i c k w e e d , Self-heal, a n d G r o u n d Ivy a n d should b e a p p l i e d w h e n t h e f o l i a g e of these a n d o t h e r shallow-rooted a n n u a l s is wet. T h i s is o n e of t h e few substances w h i c h h a v e b e e n r e p o r t e d as u s e f u l in c h e c k i n g O r a n g e H a w k w e e d . Carbolic Acid (Phenol). T h e use of c r u d e c a r b o l i c acid has b e e n reco m m e n d e d as a c o n t r o l f o r d e e p - r o o t e d p l a n t s such as D a n d e l i o n , T h i s t l e , P l a n t a i n , etc., as well as f o r Goose Grass, Eleusine indica. T h e approved m e t h o d of a p p l i c a t i o n is w i t h a n oil-can, p l a c i n g a f e w d r o p s of t h e acid in d i r e c t c o n t a c t w i t h t h e c u t s t u m p o r c r o w n of t h e p l a n t . Since this s u b s t a n c e is e x p e n s i v e a n d difficult to o b t a i n its use will doubtless b e limited. Carbon bisulfide. C a r b o n bisulfide is u s e f u l as a d i s i n f e c t a n t a n d insecticide. I t s r o l e as a weed-killer is a m a t t e r of s o m e controversy. S o m e a u t h o r i t i e s r e p o r t t h a t w h e n a p p l i e d i n l i q u i d f o r m it is effective in c h e c k i n g t h e g r o w t h of heavily r o o t e d p l a n t s such as Q u a c k Grass. I t s h o u l d b e u s e d w i t h g r e a t care, since it is n o t o n l y highly i n f l a m m a b l e b u t also p o i s o n o u s w h e n i n h a l e d . Copper sulfate (Blue Vitriol). W h e n used as a spray, in t h e c o n c e n t r a t i o n of f o u r p o u n d s to a g a l l o n of water, C o p p e r s u l f a t e has b e e n f o u n d successful in c o n t r o l l i n g c e r t a i n weeds. Its effectiveness w h e n a p p l i e d to t h e m u s t a r d s h a s l o n g b e e n k n o w n , a n d P a m m e l (1911) r e p o r t s t h a t it destroys t h e leaves of B u r d o c k , Prickly Lettuce, a n d L a m b ' s Q u a r t e r s . A fine spray s h o u l d b e used a n d t h e a p p l i c a t i o n m a d e f o l l o w i n g a r a i n . Dichlorophenoxyacetic acid (2^fD). T h i s is a n e w c o m p o u n d w h i c h is still i n t h e e x p e r i m e n t a l stages. All i n d i c a t i o n s a r e t h a t it has g r e a t possibilities as a d i f f e r e n t i a l spray. I t has p r o v e d h i g h l y effective w h e n a p p l i e d to D a n d e l i o n , B u c k h o r n , Heal-all, a n d C h i c k w e e d in c o n c e n t r a tions w h i c h a p p a r e n t l y are n o t h a r m f u l to lawn grasses. Iron sulfate (Green Vitriol). I r o n sulfate is n o t only o n e of t h e m o s t effective of all weed-killers, b u t has t h e a d d e d a d v a n t a g e of b e i n g b o t h i n e x p e n s i v e a n d easy to secure. T h e usual c o n c e n t r a t i o n is t w o p o u n d s p e r g a l l o n of water. S p r a y i n g s h o u l d b e m a d e a t a t i m e w h e n t h e i Agricultural News Letter. E. I. DuPont de Nemours & Co., Inc. p. 64, 1943. Wilmington, Delaware.

Vol. 11:

22

WEEDS O F LAWN AND GARDEN

weather is promising, for rain will wash off the solution and the process will have to be repeated. Pammel states that grasses are resistant to this spray, but that it will destroy Dandelion, Purslane, Yarrow, Ragweed, Sheep Sorrel, Velvet Leaf, Lamb's Quarters, Peppergrass, Sow Thistle, Bull Thistle, Pigweed, Shepherd's Purse, and Spurge. Oils. T h e use of various crude and fuel oils has been attempted from time to time with somewhat varying results. Muenscher (1936) states that light fuel oil may be used directly as a spray but that the heavier oils, such as crankcase drainings or waste cylinder oil, need to be mixed with lighter oil in order to permit satisfactory spraying. Sodium arsenite (Arsenite of Soda). Many of the arsenical compounds have proved efficacious herbicides, the chief objection to them being that they are extremely poisonous and must be used with great care. Sodium arsenite had best be secured from a commercial dealer in a form ready to be used rather than mixed at home. It is highly destructive to foliage, and will kill not only weeds but other plants which come in contact with it. Sodium chlorate. Sodium chlorate is one of the most valuable, yet at the same time one of the most dangerous of weed-killers. It is a powerful oxidizing agent, and substances which are covered with it are likely to catch fire u p o n drying. It should therefore carefully be removed with water from clothing and all other inflammable objects which may come in contact with it. Care should also be taken to see that it is kept covered in suitable containers. Another deterrent to the use of this compound is its expense. Applied as a spray (at the rate of one pound per gallon of water) it is lethal to most plants, even Poison Ivy. I n weaker solutions (one and a half ounces per gallon) it may be used as a selective lawn spray. Sodium chloride (Salt). Common salt has the virtue of being cheap and plentiful. It may be used as a spray (three pounds to a gallon of water) in which form it will destroy the leaves of many actively growing species. It should not be spread indiscriminately, but applied directly to those plants which are objectionable. Salt may also be used in the dry form. It is effective when placed on the stumps of certain tap roots or when spread over plants like knotweed which occur in driveways, sidewalks, or tennis courts. Sulfuric acid (Oil of Vitriol). This is a strong acid, and great care should be exercised in handling it. If it is purchased in the concentrated form, dilutions of it should be made by pouring the acid into the water, never the reverse. Also, it must never be allowed to remain on hands or clothing, for it is a powerful corrosive. As a matter of fact, the use of Sulfuric acid is so limited that it has little or no place in a general book

WEEDS AS SOIL INDICATORS

23

on weeds. It is included here to sound a note of warning concerning its use since it is frequently listed as a herbicide. Other chemicals. Several other chemicals such as Ammonium thiocyanate, Ethylene oxide, Lead arsenate, and Zinc sulfate are sometimes recommended as weed-killers. In all cases they are either in the experimental stages or their application is too restricted to warrant consideration here. W E E D S AS SOIL INDICATORS

The value of weeds as indicators of soil conditions is a subject which has received relatively little attention. It is true that the soil preferences of many plants, such as Yarrow, are so generalized that no conclusions can be drawn from their occurrence. Other species, however, are more exacting in their requirements, and their existence in a given situation may convey a hint concerning the nature of the substratum. This usefulness of plants as soil indicators is a matter which was understood empirically long before the study of soils had become a science. For example, toward the end of the eighteenth century we find John Bartram explaining how, by the addition of lime, ashes, horse-dung, etc., he improved a section of his land, adding, "By those simple means I mow, one year with another, fifty-three hundreds of excellent hay per acre, from a soil which hardly produced five-fingers some years before." 1 "Fivefingers," of course, refers to one of the trailing Cinquefoils (either Potentilla simplex or P. canadensis). In addition to the Cinquefoils, the presence in a lawn or garden of such plants as Crabgrass, Slender Rush, Sheep Sorrel, Thyme-leaved Speedwell, Cranes-bill, Self-heal, Common Speedwell, Cat's-ear, Mouseear, Hawkweed, and a number of others, may be taken as an indication that the soil has become impoverished and would profit by the application of a good top dressing. Indeed, in the case of lawns the mere digging or cutting out of such plants accomplishes little or no permanent good, since these or other species continue to appear. The explanation is, of course, that the soil has become too exhausted to support a good turf, and mere weeding will not rectify the situation. Some plants, such as the sedges, Dwarf St. John's-wort, Pennsylvania Knotweed, and Beggar-ticks, are moisture-loving species and their occurrence in lawn or garden suggests faulty drainage. Others, like Mayweed, Pineapple Weed, and Groundsel, bespeak an abundance of nitrogen (which accounts for the frequency of their occurrence in the vicinity of barnyards). Still others, such as some of the mustards, Blueweed and Gromwell, are indications of a limy or alkaline soil, whereas the pres1

H. St. J . de Crevecoeur.

Letters

from

an American

Farmer.

1782.

24

WEEDS O F LAWN AND GARDEN

ence of Sandbur or Rabbit-foot Clover may be taken as evidence of acid condition. As pointed out by H. C. Long, "the character of the land is not only indicated in some sense by the weeds which are present, but largely also by their manner of growth." Sturdy specimens of Buttercup, Thistle, Sow Thistle, Groundsel, and Dandelion are produced only on rich or loamy soils; the same species on poor land will develop in a weak or stunted manner. These remarks are offered not with a view of presenting a comprehensive account of this subject, but merely to call attention to the interest and assistance which the gardener may derive from observing the soil preferences which weeds display on his own premises.

ILLUSTRATIONS AND DESCRIPTIONS OF WEEDS NOMENCLATURE T h e species illustrated in this volume are referred to first by their common name or names. These are in all cases followed by the scientific or botanical names. T h e latter procedure is necessary in order to avoid the confusion which may arise if only the common or vernacular names are given. For example, the term "Pigweed" is applied not only to several distinct species of Amaranthus, but also to the plant more correctly known as Lamb's Quarters, a species of Chenopodium, belonging to an entirely different family. Or, again, the name "Crabgrass" may mean Eleusine indica, better known as Goose Grass, or may signify one of the species of Digitaria. Not only is the same common name often used for a number of different, and perhaps totally unrelated, species, but the same plant may be called by a variety of names, each familiar in one section of the country but entirely unknown in another. Thus, Penny Cress, Thlaspi arvense, becomes Frenchweed, Stinkweed, Stinking Mustard, Bastard Cress, and even Wild Garlic! Compare with this the practice of giving every plant two names (the first that of the genus to which it belongs, the second that of the species of which it is a representative) and the advantage becomes obvious. Prunella vulgaris is then the same thing the world over, although locally it may be known as Self-heal, Heal-all, Carpenter Weed, Sicklewort, and so on. It is true that there is occasional lack of agreement concerning the application of the botanical names. This is largely because the science of plant classification is a growing one and continues to yield a better understanding of relationships between species as well as a more accurate interpretation of the names used by earlier botanists. Thus, the Slender Rush illustrated on page 59, which was formerly called Juncus tenuis, is here called J. macer, with the earlier name (synonym) appended in parentheses. Contrary to popular belief, it is not from a desire to be capricious that botanists are constantly changing the scientific names of plants. Only such alterations as are unavoidable are made, and these solely with the intention of achieving ultimate uniformity. T h e confusion engendered by such changes is negligible compared to the chaos which attends the application of common names. 25

26

WEEDS O F LAWN AND GARDEN

T h e nomenclature followed in this volume is, in the main, that of Gray's New Manual of Botany, Edition 7. Exceptions have been made only in the case of a few species which have undergone a valid change of name. In these instances the name used in Gray's Manual follows parenthetically the now accepted designation. ARRANGEMENT T h e sequence of families followed in this work is that which has been adopted in nearly all standard manuals of botany in this country, and is based upon the Engler and Prantl natural system of classification. This possesses the advantage of enabling those who are already acquainted with the relative positions of these major groups to locate quickly any family which they are seeking in these pages without reference to the index. Conversely, those for whom this work may serve as an introduction to the world of plants will find that the familiarity with the evolutionary arrangement gained herein will result in their feeling at home in those larger and more technical works which they may thus be stimulated to consult. Within the limits of each family the genera are, for the size of convenience, arranged in alphabetical order. Exceptions to this will be found only in the very few cases in which, to conserve space, two genera of the same family have been illustrated on the same plate. Within the genus, however, the species follow the evolutionary sequence, which has the advantage of bringing related species together. This procedure, which may at first sight appear inconsistent, will, it is believed, make for ready reference once the reader becomes familiar with it. ILLUSTRATIONS All illustrations in this book are one-half natural size, except as otherwise indicated (i.e. the symbol X 2 means twice natural size).

GRASS FAMILY (GRAMINEAE)

Floret

27

lemmas of the individual florets

A

outer cjlume hzmma

inner

antkzr-si

outer

X 1o One-flowered spikelet

(AG RQSTIS)