Wherever plants known to be poisonous are found, some effort should be made to destroy them, or prevent at least their multiplication. In most cases they may be simply dealt with as weeds, as annuals, biennials, or perennials.
Annuals: Annuals, which produce their flowers and seeds in one season, have no other means of propagation than seeds. Therefore any method, best chosen by the individual farmer, which will prevent the production of seeds will exterminate the plant. As the purple cockle, cursed crowfoot and Indian tobacco are all annuals, much loss may be avoided by mere hand-pulling or cutting when these plants are in flower.
Biennials: Biennials, which bloom and ripen their seeds the second year, may be treated as annuals as far as the production of seed is concerned. They will eventually succumb to continued close cutting or to the use of the hoe or spud. Thorough cultivation and drainage where necessary is the better method on large and badly infested areas.
Perennials: Perennials are propagated both by seeds and by underground rootstocks, bulbs, or tubers. The prevention of seed production is quite as important as the destruction of the underground portion of the plant, in many cases, more so, as the numerous light seeds borne to fresh soil will in time produce many more new plants than is possible by the division of the rootstocks. But in other cases, as for instance the water hemlocks, the portion in the soil is the most deadly, and any small piece uprooted and eaten by stock will result in death in a few minutes. Thus it is necessary for the extermination of the species and the safety of human beings as well as animals to destroy all portions of poisonous perennials by the quickest means possible.
Spraying: Chemical sprays may be used to advantage; they are economical and effective in most cases. Plants with rough leaves are most susceptible, as the spray clings to the surface more readily. Smooth leaves shed the spray before it has time to take full effect. The spray should be applied in a fine mist on a bright clear day when there is no likelihood of rain undoing the work. Spraying is most effective when the plants are young and succulent, that is, just before they flower or in their first bloom.
Common Salt or Sodium Chloride: Common salt is one of the cheapest and safest sprays to use. It is most destructive when applied in hot dry weather, as it absorbs the moisture from the plants and the surrounding soil to such an extent that the plants die of thirst. A solution of 150 pounds to 60 gallons of water may be used, or where all vegetation is to be destroyed it may be applied in the form of hot brine, of such a strength as to show crystals on its surface.
Caustic Soda or Sodium Hydroxide: This chemical is especially useful in destroying poisonous plants on waste ground or places where vegetation is negligible for a season. It may be used with good effect on poison ivy, spreading dogbane, and similar deeply rooted weeds. A 5-per cent solution, or one pound caustic soda to two gallons of water, is sufficiently strong for ordinary purposes. All other vegetation will be checked until this chemical is washed out of the soil.
Iron Sulphate or Copperas: Copperas is comparatively inexpensive and may be used on poisonous plants which may be growing among grain, grass, or pea crops. It will do no harm to these crops, but cannot be used where beans are planted. Clover and alfalfa plants are blackened by it, but they will quickly recover if the solution has not been too strong. The usual solution is obtained by dissolving 100 pounds copperas in 52 gallons of water, which quantity is sufficient for one acre of herbage.
Copper Sulphate or Bluestone: Bluestone is more expensive, but a far less quantity will serve the same purpose. From 8 to 12 pounds is sufficient for 52 gallons of water. Both copperas and bluestone spraying should be done in clear, hot weather, when rain is not expected for at least twenty-four hours.
The following list, in each case, does not include all the plants that are poisonous to the different animals, but only those through which most loss has been suffered.
Swine: Darnel, purple cockle, water hemlock.
Poultry: Ergot, darnel, purple cockle, and other injurious seeds in screenings.