Seeds and seed treatment.
Of all the features of cropping which allow of direct effort toward controlling or avoiding disease, the seed is open to the easiest and most effective study. It is an old saying that the seed-time de cides the harvest. It might as truly be said that the type of seed, how it is cared for and handled and prepared for the soil, decides what the harvest shall be. This is particularly true with types of plants that are subjected to certain crop diseases.
In handling the seed preparatory to the greatest possible control of plant disease, one should always have in mind a number of very important factors. The introduction of new varieties into standard cropping regions is often attended with troubles arising from disease introduction. Some varieties may not only prove worthless because of lack of disease-resisting powers, but also may often prove to be great disseminators of disease to the standard crop of the locality. This feature may be noticed in all types of plants, but is markedly noticeable among cereals with reference to rust, as in differ ent varieties of oats and of wheat. For example, it is very probable that the introduction of winter varieties of wheat into noted spring-wheat areas is alone sufficient to account for the rapid disappear ance of the spring crop, this result being brought about by rust which early developed on the winter crop and fell on the immature spring crop. For similar reasons, mixtures of varieties should be avoided when possible. This is especially true of cereals, but applies equally to fruit and vegetable culture. When attempting to control crop diseases, it is a matter of the greatest concern that in the crop there should be an evenness of development and maturing. One can often protect plants or crops of the same grade of growth or maturity, but it is difficult to avoid damage when there is no uniformity in these features.
Saving seed.—After purity of variety, there are no features of caring for the seed of greater impor tance than those which insure proper harvest, curing and storing. Aside from conditions that may cause weakened vitality of the seeds, there are many features of these processes that may introduce or multiply the chances of introducing infectious dis eases. Each crop and its special diseases must be
studied with these points in mind.
Vitality or initiative growth power in the seed or cion is of great importance. It is of much moment that the growth period from seed-time to maturity shall be as short as possible. This applies especially to annual crops. This initiative seed power can be gained and maintained only by per sistent seed selection, cleaning and grading. With this point in mind, one selects to secure varieties and individual types which are the least susceptible to disease, cleans them thoroughly to free them from possible disease-bearing parts, and grades them to get rid of diseased seeds, those that are predisposed to disease and those that are not up to the standard of excellence. Note Figs. 72-74.
Treatment of seed.—Proper seed treatment pre supposes a proper selection of seed, proper cleaning and grading. Seed thus prepared is then ready for treatment or disinfection. The theory of seed dis infection rests on the principle that some plant diseases, indeed many, are transmitted by way of the seed either to the soil or to the new plant directly by way of the embryo.
Taking up this feature of the question, it is necessary to consider just what diseases are to be prevented. Some are known to be directly trans missible by way of the seed, the embryo or germ layers being internally infected as in the case of flax-wilt or anthracnose of beans and loose smut of wheat. By far the greater number of diseases, such as the stinking smut of wheat and onions and numerous diseases of garden vegetables, including potato-scab and potato-rot, however, are easily transmitted to the ground and the new plant because of the presence of external spores, struc tures that are simply dusted on the seeds, and only await an opportunity to prey on the roots. (Fig. 75.) For all such diseases, seed disinfection is an easy and direct remedy, and numerous formulas and washes or solutions suited for special diseases have been developed from time to time, among which may be named the following examples : Cop per sulfate solution, corrosive sublimate solution, hot water treatment, and the formaldehyde treat ments.