# Popular Science Monthly/Volume 41/June 1892/Pestiferous Plants

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* PESTIFEROUS PLANTS.
By Prof. BYRON D. HALSTED,
BOTANIST OF NEW JERSEY AGRICULTURAL COLLEGE EXPERIMENT STATION.
SOME plants, naturally, are better fitted to subserve the wants of man than others, and for the growth of these he puts forth special effort; in short, the whole underlying foundation of modern agriculture rests upon methods of favoring these plants and thereby enlarging and multiplying those qualities in them that led to their being chosen by man as objects of cultural attention. All plants, therefore, that now legitimately occupy space in our fields, orchards, and gardens are living an unnatural life, because they are in part creatures of selection and care; and it therefore follows that, owing to this stimulus under which they have flourished for generations, when the fostering hand of man is withheld they either perish or gradually drift back to the wild state and slowly lose many of their most valuable qualities as cultivated plants and regain those that better fit them for the stern battle of life. During the time while cultivated plants have been brought to a high plane of usefulness there have been many other species with no merit in their products that have stood in the way of the development of these fostered plants. The weeds have grown strong because obliged to fight their way and take every possible advantage when opportunity offers. They quickly win in the race for supremacy in every field devoted to cultivated crops, when man's care is withheld, and multiply their kind to an extraordinary extent. More reasonable it would be to expect a man under the softening influences of civilized life to win in the rough race for existence when placed, unaided, among savage Indians, than to hope for the success of a parsnip or onion seedling when surrounded by a rank growth of weeds.
There is nothing in the structure of a plant that Cain-like curses it forever. No part of the leaf, stem, fruit, or flower gives conclusive evidence that it belongs to a weed, and therefore we are forced back to the definition that was accepted a long time ago, namely, "A weed is a plant out of place." Its relation to others makes a plant a weed. A rose bush of the rarest variety, and one highly prized in its proper place, is a weed when occupying the soil to the detriment of some other plant that has the ​authorized right to the soil. Clover and the best of grasses may be serious weeds, fit subjects to be uprooted by the cultivator or hoe, when growing in a corn-field and injuring the maize crop. If a field is devoted to wheat, it follows that all other plants therein may be weeds, whether it be cockle, red-root, or an oak tree.
There is a possibility of any kind of a plant being a weed, but this thought does not prevent some species always being out of place. For example, there is no function in the economy of the farm garden that the Canada thistle can do as well as many other plants. As a forage plant, or a source of nutritious seeds or beautiful flowers, the pig-weeds are a substantial failure, equaled only by their success in occupying the soil and robbing it of nourishment designed for useful plants. It would puzzle any one to find a proper place for the horse-nettle, now advancing upon the Eastern farmers from the Southwest, and destined to spread its horrid, prickly, worse than worthless branches over our cultured soil. The bur-grass, cockle-burs, burdock, and a long list of congeners are practically universal every-day curses from which all earnest crop-growers wish to be free.
The natural covering of a fertile soil is a growth of vegetation. Upon the broad, open prairie there is a dense coat of grass, while in the Eastern States a heavy growth of trees clothed the virgin soil. So strong is Nature's desire to assert this right that if we allow one of our fields to lie fallow, at the end of the season it will be covered with vegetation. She understands that a bare soil is a wasteful soil, for while it is not producing anything it may lose by leaching much fertility already in its bosom. Every generation of plants inherits the deposits of all previous generations, and in turn should add to the accumulated stock in the soil. By this economical and saving practice of Nature the fertile newly broken grass lands have been made, while the upper soil in the forest has received the enriching accumulations of ages. Man overturns this harmonious system, and by breaking up the sod destroys the very method by which sod is made. He clears away the forest and many of the conditions which favor the growth of trees. It is upon this newly exposed soil that weeds assert their supremacy, and if the hand of man is withheld they will soon weave a garment, in itself unattractive, that clothes the bare earth. Weeds have a thousand ways of doing this to one possessed by cultivated plants. Bring up, if you please, some soil from the bottom of a newly dug well, and if exposed for a season some weeds will have planted colonies upon the bare heaps and vied with each other for the entire possession of the new territory, at the same time gaining in forces for the occupation of any similar place elsewhere.
​The crop-grower necessarily introduces the condition of a bare soil for a portion of the year for every crop, and must therefore accept the situation: while he invites their presence and development, even stimulating them in various ways by making the conditions favorable for the growth of his crop plant, he must become a competitor with the weeds for the possession of the soil. The weed seeds are either in the soil or soon find an abundant entrance, and if the way is clear the young pests are up and doing as with the morning sun.
Most of our weeds, like much of our vermin, have come to us from beyond the sea. Just how they emigrate in every case will never be known; some came as legitimate freight, but many were "stowaways." Some entered from border lands upon the wings of the wind, on river bosoms, in the stomachs of migrating birds, clinging to hairs of passing animals, and a hundred other ways besides by man himself. Into the New England soil and that south along the Atlantic seaboard the weed seeds first took root. Also the native plants, with a strong weedy nature, developed into pests of the farm and garden. Many of the native weeds are shy and harmless in comparison with the persistent and pugnacious ones that have like vagabonds emigrated to our shores. Why should it be that plants of another country not only find their way here, but after arriving assert themselves with a vigor far surpassing our native herbs? Dr. Gray, in writing upon this point, says, "As the district here in which the weeds of the Old World prevail was naturally forest-clad, there were few of its native herbs which, if they could bear the exposure at all, were capable of competition in the cleared land with emigrants from the Old World." The European weeds had through long ages adapted themselves to the change from forest to cleared land, and were therefore prepared to flourish here in the rich forest soil that was suddenly exposed to the sun and subjected to other new conditions by the felling of the trees. To go back of this we are not sure that the ancestors of some of our European weeds ever came from the forests, but instead were brought into the cleared-up lands from open regions in the early days of agriculture in the Old World. As civilized man moved westward, the weeds followed him, re-enforced by new native ones that soon vied with those of foreign blood. Not satisfied with this, these natives of the interior ran back upon the trail and became new enemies to the older parts of our land. The conditions favorable for the spreading of weeds have increased with the development of our country, until now we are literally overrun. Weeds usually as seeds, go and come in all directions, no less as tramps catching a ride upon each passing freight train than in cherished bouquets gathered between stations and tenderly cared ​for by transcontinental tourists in parlor cars. "Weeds," Burroughs says, "are great travelers. . . . They are going east and west, north and south, they walk, they fly, they swim. . . . They go under ground and they go above, across lots and by the highway. But like other tramps they find it safest by the highway; in the fields they are intercepted and cut off, but on the public road every boy, every passing herd of sheep or cows, gives them a lift." They love the half-earnest tiller of the soil, and will crowd around his barns and dwelling, and flourish in his garden and fields so long as he favors them with slight attention to his crops.
The fact is patent that weeds are everywhere, and the best means need to be taken to resist their greater prevalence. In this warfare against them there is no weapon equal to a thorough knowledge of the enemy that is, an understanding of the nature of these pests, their appearance in all stages of growth, methods of propagation, and dissemination of the seeds. This knowledge is much more highly appreciated in Europe than here. In Germany, for example, they have wall maps upon which the leading weeds are represented. Hung as these are upon the school-room walls, a child, simply from daily seeing these life-like colored drawings of the various pests, will learn their appearance and names. Some such method of instruction is needed in this country, by which the children who are soon to be our farmers and gardeners may become familiar with the troublesome weeds even in advance of their advent, that the proper means may be taken at once for meeting and destroying them. Editors of agricultural papers and professors in agricultural colleges yearly receive many letters asking for the simplest kind of information concerning many common weeds, thus showing the general lack of knowledge upon this important subject. To put a map of a dozen of the most destructive weeds upon the walls of every country school-house in the United States is a great undertaking; but if it were done, the next and succeeding generations of farmers would be the better able to carry on the work of extermination. There are a large number of farmers' clubs throughout the country, and a great deal might be done by hanging a weed chart upon the walls of these halls where farmers gather from time to time for mutual improvement and a better understanding of the ways and means of a more profitable agriculture.
Weeds have been neglected in more ways than one, and just so far as they are overlooked and left to themselves the greater will be the curse. As one looks over the premium lists of our thousands of county and State fairs one seldom sees a prize offered for the best collection of weeds. It seems incompatible with our fitness of things to have a good collection of anything that is bad; ​and yet the fact remains that there is no class of plants about which an increase of knowledge is more imperative than these same ugly weeds. A few dollars expended in awards by each fair association would bring together lists of plant pests the exhibition of which would not only surprise but greatly instruct those who see them. It is not less important for the farmers of any district to know of the arrival of a new weed than of the advent of a new fruit or grain.
In this connection, and in conclusion, it is a pleasure to announce that space at the World's Columbian Exhibition has already been set aside for a display of the weeds of the whole country, and preparations are now making for a full occupation of the allotment.