While the bean has a number of insect enemies, the weevil is the most destructive. This insect is about 1/8 inch long and covered with fine brown, gray and olive pubescence. Ovi-position begins in the field, where the female deposits eggs in holes in the pods made by the jaws or by the drying and splitting of the pods. Breeding continues after storage, a large number of individuals frequently developing in a single bean. The beetles emerge the following spring to repeat their work of destruction.
Field treatment of any kind has not been satisfactory, so that preventive measures before planting must be employed. Fumigation with bisulphide of carbon is the most effective treatment. The New Hampshire Station (N. H. Bul. 59) recommends the following plan: "Use an ordinary coal oil barrel, which will hold close to five bushels of beans. This can be treated with 3 ounces of bisulphide of carbon, which may be poured on the beans. Care must be taken to close the top tightly; the exposure should be for 48 hours. The bisulphide should be of the best quality because this will vaporize without any residue. The vapor of this substance is very inflammable and the work should, therefore, be done at a distance from other buildings and no light of any kind be brought near".
Anthracnose (Colletotrichum lagenarium) is the most common and the most destructive of the bean diseases. It is a fungous disease, which attacks all parts of the plant except the roots. Diseased seed is often the source of the malady. The young tender stems rray become affected and the plants killed when conditions are favorable for the parasite; or it sometimes appears later on the pods, as well as on other parts of the plant. The disease is very noticeable on the yellow pods of wax varieties, which they reduce in value or render unfit for market purposes. Figure 62 illustrates the diseased pods. The Cornell Station (Cornell Station Bulletin 255, p. 436) makes the following statement in regard to this disease: "The spots or cankers are black with reddish or yellowish margins. Most growers are also familiar with the disease on the seed itself, especially on the white beans, where it makes rusty, red spots of various sizes, sometimes involving nearly the entire seed, though ordinarily only producing a slight discoloration on one side. The disease enters the seed by way of the pod, the fungus penetrating from the outside into the young and tender seed. . . . When the diseased seeds are planted in the soil, and first come through the ground, they are sure to show the small black cankers on the cotyledons or seed leaves and a little later on the stems".
Fig. 62. bean antiiracnose.
Numerous investigations have been made pertaining to the control of bean anthracnose. Seed treatments of various kinds and spraying have been tried, but with unsatisfactory results. The planting of healthy seed is unquestionably the best preventive measure. If seed and soil are free from the disease, there can be no anthracnose. Seed selection, then, is of prime importance, and the matter should have closer attention among both home and commercial growers.