52 



THE MEANS OP CONTROLLING PLANT DISEASES 



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 thj 

 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 

 education 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 

 yalue. 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. 



This line of work lately has been found to give 

 results of enormous crop value. One has only 

 to save the seed from the types that best serve 

 the purposes, and persist in doing so to gain 

 greatly in this respect. This is the newest field of 

 work along the line of controlling plant diseases, 

 but it is sufficiently past the experimental stage 

 to allow one to assert with confidence that any 

 farmer who will may thus greatly benefit himself 

 and aid all mankind toward the elimination of 

 plant diseases. For example, if we gain a type of 

 wheat that does not produce on its leaves one-third 

 as much rust as has been produced previously in 

 that region on the common types of wheat, it is a 

 self-evident fact that there will not be so much 

 rust to be distributed to other fields. If, by care- 

 ful and consistent selection of varieties and indi- 

 vidual strains from the varieties, the farmer 

 finally attains a crop of potatoes that is no longer 

 open to the attack of potato-rot and potato-blight, 

 it is a self-evident fact that his fields will not be 

 distributers of the disease to other fields. It is too 

 much to expect, perhaps, that this process will 

 eliminate entirely some of the most destructive 

 diseases, such as rust of wheat, rot of potatoes, 

 blight of pear, root-rot of cotton, and wilt of flax, 

 yet the results gained in this direction in the past 

 ten years are such as to convince the most skep- 

 tical that herein lies a most effective means of 

 reducing the destructive action of plant diseases. 

 The process is so simple that any one may engage 

 in it with success. Diseases weaken, mar, shrivel 

 and lessen the produce from plants that are non- 

 resistant. Mother plants that are resistant produce 

 the more perfect products. It is from such that 

 one should propagate the succeeding crops. It is 

 but to put the " survival of the fittest " principle 

 into direct action in crop production. 



Literature. 



The literature on plant diseases is voluminous. 

 It is impossible here to cite monographs. Refer- 



