A Weed is a plant that is not wanted. The methods of weed-control depend largely on the character of soil, system of farming practiced in the neighborhood, and, particularly, on the type of weed concerned, whether annual, biennial, or perennial. The better the crop-scheme, the less will be the difficulty from bad weeds. The prime remedy, therefore, is to improve the general farm plan and practice, and to use only clean seed. Special means and methods may be discussed, however; and these discussions are drawn from Farmers' Bulletins of the United States Department of Agriculture, from bulletins of the Rhode Island, Ohio, and North Dakota Stations, Cyclopedia of American Agriculture, and other sources.

General Practices

For annual weeds, which reproduce from seed only, the root and branch dying each year, the essentials for eradication are the use of clean seed, the killing of plants before they ripen seeds, and the prevention of new infestation by such means as manure from stables where weed forage has been used. For permanent pastures, lawns, and roadsides the prevention of seed production is often the most practicable method, and it is sufficient if persistently followed. In cultivated fields the land thus seeded may first be burned over to destroy as many as possible of the seeds on the surface. It may then be plowed shallow, so as not to bury the remaining seeds too deeply. The succeeding cultivation, not deeper than the plowing, will induce the germination of seeds in this layer of soil and kill the seedlings as they appear. The land may then be plowed deeper, and the tillage repeated until the weed seeds are cleared out to as great a depth as the plow ever reaches. Below that depth, eight to ten inches, very few weed seeds can germinate and push a shoot to the surface. Barren summer fallowing is often practiced to clear out weedy land by the method just described; but usually a cultivated crop may better be grown.

For biennials, which also reproduce from seed, mowing them when coming into flower or cutting the roots below the crown is usually effective. Autumn is the best time for such grubbing. Biennial weeds are readily killed by such tillage as is given to hoed crops.

For perennials which reproduce both from seed and from surface runners or perennial underground roots or stems, seed production must be prevented and the underground part must be killed. Seed production may be prevented by mowing when the first flower-buds appear. The best methods for killing the roots or rootstocks vary considerably according to the soil, climate, character of the different weeds, and the size of the patch or the quantity to be killed. In general, however, the following principles apply: 1.   The roots, rootstocks, bulbs, and the like, may be dug up and removed, a remedy that can be practically applied only in small areas.

2.  Salt, coal oil, or strong acid applied so as to come in contact with the freshly cut roots or rootstocks destroys them for some distance from the point of contact. Crude sulfuric acid is probably the most effective of comparatively inexpensive materials that can be used for this purpose, but its strong corrosive properties render it dangerous to handle. Carbolic acid is less corrosive, and nearly as effective. Arse-nite of soda and arsenate of soda, dangerous poisons, are effective, particularly the former, applied as a spray on the growing weeds. Fuel-distillate, a petroleum product, is very promising.

3.   Roots may be starved to death by preventing any development of green leaves or other parts above ground. This may be effected by building straw stacks over small patches, by persistent, thorough cultivation in fields, by the use of the hoe or spud in waste places, and by salting the plants and turning on sheep in permanent pastures.

4.   The plants may usually be smothered by dense sod-forming grasses or by a crop like hemp, buckwheat, clover, cowpeas, or millet that will exclude the light.

5.   Most roots are readily destroyed by exposing them to the direct action of the sun during the summer drought, or to the direct action of the frost in winter. In this way plowing, for example, becomes effective.

6.   Proper crop rotation is one of the best means of eradication.

Chemical Weed-Killers or Herbicides

The usefulness of chemicals as weed-killers is largely limited to the following cases (Jones): 1.   When an especially obnoxious weed, as poison ivy, occurs in a limited locality and is to be destroyed regardless of consequences to soil or neighboring plants.

2.   When the aim is to render the soil permanently sterile, as in roadways, tennis courts, and the like.

3.   When the weed plant, as orange hawkweed and mustard, is much more sensitive than the associated useful plants to the action of some herbicide.