In the case of crops that are annually attacked by diseases, an intelligent, concerted action on the part of the farmers throughout the country must, of necessity, have great bearing on the reduction of disease-producing influences. Every farmer knows that to grow potatoes year after year on the same patch of ground results in gradual reduction in yield and quality because of scab, rot, blight and wilt, and numerous apparent but unknown troubles. This is but an example of the accumulation of the infecting spores of such diseases in a particular area of soil or in the immediate neighborhood. There are probably none of the fungi producing known diseases, that are not able to survive the winter on the refuse of the preceding crop. We have numerous such examples: mildew of peas and beans, bacterial disease of cabbage, cotton root-rot, wilt of flax, stinking smut of wheat, the black smut of corn, potato-blight and potato-rot, apple-scab, apple canker, pear-blight, grape-rot, and so on. While some of these diseases are maintained from year to year on wild plants, the great majority of them gain their excess of development on the more ten der abnormally developed agricultural. plants. It has thus become one of the tenets of agriculture that the waste products of these, such as potato tops, waste fruit or vegetables, whatever they may be, should be eliminated as quickly as possible. This may be accomplished by gathering them care fully in heaps to be burned on the ground, or per haps better by thorough composting. It has been said that thorough composting results in the de struction of most types of spores ; yet, on the out side of all such manure piles and compost heaps it has been found that many of the diseases, such as the smuts and imperfect fungi, may even develop their spores in great quantities. The writer has known whole areas of virgin soil in North Dakota to be ruined for flax production through the use of poorly composted flax straw in barnyard manures.
Old-time gardeners have always believed in the elimination of weak and sickly plants. Greenhouse men of greatest success have always "rogued" all their beds. It will be clearly seen that, if such weakly and sickly plants are destroyed by fire, the chance of spreading disease is greatly lessened. In the case of perennial plants, trees and shrubs, there are many diseases for which proper pruning may largely lessen the possibilities of disease distribu tion. In the case of apple-blight, pear-blight, and many of the common fruit diseases, a persistent cut ting back of the diseased parts and burning is suf ficient largely to reduce the damage done by these very destructive diseases. Indeed, at present it seems the only effective means of controlling such diseases. In these cases which directly infect th internal tissues of the plants, the pruning to elim inate diseased parts must be done at a consider able distance below the actual place of disease in order that the disease may not continue below that point. One also keeps a disinfecting solution for the purpose of disinfecting his hands and tools, so that the disease may not be transferred from limb to limb. In the case of pear-blight, which may be taken as a good example of such troubles, the organism that occasions the blight may be trans ferred in the sticky juice that exudes from dying parts to other parts by any agency which comes in contact with the disease-bearing liquids and afterwards wounds or perforates delicate parts of other trees. A concerted action of the fruit
growers throughout the United States might readily reduce to a minimum the injury occasioned by this disease. In order to make such efforts effective, farmers interested in particular crops, whether of fruit, vegetables or cereals, will need to bring as much influence as possible to bear on their neighbors, and indeed on all persons con cerned. It is only in concerted action that sanitary prevention can become of general benefit. When elucation along such lines is general, losses from disease will be reduced to a minimum.
A point in disease control which is often over looked by many who are otherwise quite successful, is that of caring for the seeds after harvest. This especially applies to vegetables and cereal grains. All bins, machinery, granaries, storehouses and elevators should be kept thoroughly clean and, as nearly as possible, free from dust. The farmer who practically breeds and selects his own seed grain and plants for propagation, after once having procured a pure strain, need seldom take other precautions than those previously mentioned of eliminating the weak and inefficient plants and the like, providing he holds himself to cleanliness in regard to machinery and seed storage. It is easy to introduce such a disease as stinking smut of wheat, by allowing the machine which has pre viously threshed a smutty crop to come on the farm before it is properly cleaned. It is clearly evident that diseases of cereals and vegetables, including potatoes and smaller crops, can be transmitted readily in sacks and other containers. In most cases it is a simple matter to disinfect these con tainers at the time that the process of seed disin fection is being carried out.
Breeding and selection.
All of the above processes that have been men tioned for avoiding or controlling diseases have for their basis the assumption of the fact that we have a particular kind or strain of plant or crop that we wish to protect against disease. Control ling diseases of farm crops by means of breeding and selection has in view the supposition that those valuable strains of farm plants which we now possess, by proper breeding and selection may be increased in their efficiency of resisting disease without materially interfering with their economic value. Proper processes of breeding and selection, therefore, would presuppose the ability on the part of the breeder or selector to maintain, in his crop, its ability to produce quantity and quality and yet have the crop possess the added power of disease resistance. To accomplish this does not demand the effort of a scientific plant-breeder alone. It demands that the farmers gain that simple knowl edge that enables them to recognize the plant or crop that does resist the prevailing diseases, and then that they should save the seed and propagate this crop to the exclusion of those types of plants or crops which are inefficient in this respect. New kinds are often secured by the process of crossing and breeding. This is usually the work of the expert or, at least, of men who have means and time to tend to the work. But new strains, so far as the actual crop is concerned, may be secured by straight selection of individual plants.