Usually the treatment demands that individual seeds shall be subjected thoroughly to the action of the disinfecting medium for a definite period of time. It is well to remember that, as in the case of serving medicine to persons, or administering washes to wounds, only certain strengths are suit able to particular cases. Therefore, the directions for using must be followed closely if prevention can be reasonably expected, the aim being to pre vent the disease, and, at the same time, in no way to injure the growth from the seed. It is an inter esting feature of seed disinfection that, whenever a proper treatment for prevention has been made, the yield may very greatly exceed that from the untreated seed of the same type, even though no particular disease is known to infest the seed. This may be readily accounted for by the fact that dis infection does away with many unknown or unob served organisms on the seed that cause trouble to the young plant sufficient to be of great detriment to its growth, and yet not sufficient to give results that would ordinarily be characterized as dis ease. Thus, with seed properly treated by the for maldehyde method of disinfection, bacteria, yeasts, molds, all types of organisms which readily set up fermentations in the moistened seed, are disposed of, leaving the young plantlet to draw unmolested the full amount of food materials stored in the mother seed.
The following farm crops are grown with much greater advantage if the seed is first disinfected : Wheat, barley, oats, millet, grass seeds, flax seed and corn. The method of disinfection is now almost uniformly some modification of the formaldehyde treatment.
Formulas for seed a few of the standard formulas for seed treatment may be noted here. The steps in different cases are very similar. Persons interested in some special method of seed treatment should consult their nearest experiment station officer interested in such work, or look up the matter in the general literature of the stations and the Department of Agriculture.
Hot water : Temperature and time of immersion vary according to kind of seeds and type of dis ease ; especially recommended for stinking smut and the smuts of oats and barley ; for stinking smut in wheat dip at 135° Fahr., for three to five minutes ; for oat- or barley-smut, immerse at 133° Fahr., for fifteen minutes. (Consult bulletins of Indiana, Kansas, North Dakota, and other experi ment stations.) Corrosive sublimate solution : One ounce to six gallons of water ; used successfully to treat potato tubers for destruction of spores of scab, rot and blight ; immerse whole tubers for one and one-half hours. Plant on disease-free soil. This solution is also very effective against stinking smut of wheat. (See bulletins of North Dakota Experiment Sta tion and others.) Formaldehyde solution : The most economical and successful seed disinfectant ; now in general use for all types of seed and all types of plant dis eases. Especially recommended for prevention of smuts in cereal grains, wheat, oats, barley and millet, flax-wilt, onion-smut and potato-scab. Very
effective in improving the first-growth powers of weak or moldy seeds, especially grass seed, corn, garden seeds, and the like. It prevents the early action of molds, damping-off fungi and other diseases. The strengths used on cereals and seeds is generally sixteen ounces of 40 per cent formalde hyde to forty gallons of water ; for potato-scab, sixteen ounces to thirty gallons. It is used either as a spray or dip. (For special methods, consult experiment station literature.) Sulfur and lime have often received high com mendation for use in seed disinfection. The writer, after many trials, has been unable to find them of use against any fungus which attacks by way of seed or soil.
The growing crop or plant.
It is essential to take into consideration the growing plant or crop, noting the many features that have particular hearing on disease develop ment or, at least, those that allow one to guard the crop against excessive destruction. Any feature of soil or environment which may chance to give an unfavorable growth period during the regular growing season may lay the crop open to serious damage. Thus, the drainage and character of the soil, as already said, and its cultivation may par ticularly affect the character of the crop with reference to its ability to develop in the presence of disease. The influence of drainage is always distinctly noticeable in its effects on the develop ment of blights, wilts and rusts. For example, poorly drained areas in the great spring - wheat belt of the Northwest bring about heavy dew for mations, and this results in extreme rust infection and consequent damage.
The matter of fertilization of the flowers by insects often plays a direct role in introducing new infection, as, for example, when bees and flies visit infected trees and carry infection from flower to flower and from tree to tree. This has been clearly demonstrated in pear- and apple-blight.
The application of fertilizers and barnyard manures may exert a direct influence on the devel opment of plant disease. One often sees the ill effects of the injudicious use of such agents. It need only be emphasized that an unbalanced food supply readily produces an irregular growth which may be open to the attack of many types of disease-producing agents, as, for example, rust of wheat in case of excessive use of nitrogenous fer tilizers or barnyard manures. Weeds in many ways may be unfavorable in their effects on the grow ing plant, and directly favorable to destructive action of plant parasites on the crop. They draw away nourishment in time of drought and by keep ing the crop befogged in times of dampness, as in the case of the rust parasites, they bring about profuse spore germination and infection. Certain weeds are also direct breeders of the parasites which prey on special cultivated crops. Clean cul ture, therefore, always has its direct merits.