THE MEANS OF CONTROLLING PLANT DISEASES 



51 



sidering the stage of leaf, flower or fruit develop- 

 ment. Usually the earlier spraying is done on 

 orchards and permanent plants, in order to destroy 

 the first series of spores that may come from dis- 

 tant regions. Two or three, and in some cases four 

 or five treatments are applied during the growing 

 season for a like reason. 



If spraying is done properly, one need not expect 

 to see much indication of the diseases which are 

 thus preventable in the sprayed crop. It is wholly 

 a matter of prevention. Therefore, forethought 

 rimst be exercised ; for when the disease is once 

 started, spraying, in most cases, will not prevent 

 the particular plant sustaining injury, as in the 

 case of a potato plant which has become attacked 

 by blight. Proper spraying, however, will prevent 

 the disease spreading from this plant to other 

 plants, — indeed, will keep it confined to the parts of 

 the plant already attacked. Even the individual 

 plants that are once attacked are benefited because 

 their future growths may continue uninterrupted. 

 Spraying has become so universal that one need 

 only cite a few diseases that are thus preventable. 

 It must be remembered that, as each plant disease 

 has a particular life-history and attacks its host- 

 plant in a particular way, there are special reasons 

 for modifying spraying processes to fit each crop 

 and each peculiar disease; therefore, one who 

 wishes to take up the work should consult proper 

 authorities, or bulletins dealing directly with this 

 phase of the question. 



The following list of diseases that may be pre- 

 vented by proper spraying is only an indication of 

 the actual number : Apple ripe-rot, anthracnose, 

 canker or bitter-rot, leaf-spot and scab ; aspara- 

 gus-rust; bean anthracnose; beet leaf -spot; celery- 

 blight; cucumber damping-off, mildew and blight; 

 gooseberry mildew ; grape-rot and anthracnose ; 

 lemon-scab; lettuce leaf-rot, leaf-mold and mildew; 

 melon mildew and anthracnose; olive-scab; orange- 

 scab and mold ; peach leaf -spot and scab ; pear- 

 scab and leaf -spot ; plum-rot and shot-hole fungus ; 

 potato early blight, late blight, rot and mildew; 

 raspberry anthrancnose ; squash fruit-blight, rot 

 and mildew; tomato anthracnose, leaf-bliglit and 

 damping-off ; violet mildew, mold and blight. 



Sanitary prevention. 



Since all of the plant diseases that affect field 

 crops and plants generally, excepting^ those that 

 are due to improper agricultural technique or par- 

 ticular chemical nature of the soil, may be looked 

 on as essentially infectious, either directly from 

 plant to plant or from soil to soil, one may put the 

 whole matter on sanitary bases similar to those 

 which apply to the prevention of diseases among 

 animals and man. An ounce of prevention is worth 

 a pound of cure. In the case of farm crops and 

 garden plants, it is clearly true that a slight 

 amount of energy placed to the credit of proper 

 methods of prevention adds greatly to the crop 

 returns. The chief methods of prevention that are 

 usually practiced have be6n cited when we mention 

 seed treatment and spraying. These strictly belong 

 to this heading of sanitary prevention, but, as they 



have become matters of common practice, the 

 writer wishes to call attention to the fact that 

 there are other sanitary methods of avoiding 

 diseases in farm and garden crops aside from these 

 two. Much may be done to put the environments 

 of the crop in sanitary condition, as the cleaning- 

 up of the field after the previous crop, the elimina- 

 tion of diseased parts of permanent plaftts, trees 

 and shrubs, the disinfection of bins, machinery, 

 sacks, storehouses, elevators and all containers and 

 contrivances that are to be handled in connection 

 with the cultivation of the new crop. And, finally, 

 the farmer should look to the breed, striving to 

 procure breeds or strains that are resistant to the 

 diseases that affect their race and variety. 



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 



