5a 



THE MEANS OF CONTROLLING PLANT DISEASES 



uniformly some modification of the formaldehyde 

 treatment. 



Formulas for seed treatment. — Only 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 bearing 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 r61e 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. 



The matter of considering the growth periods of 

 the crop becomes one of actual necessity when 

 preparing for the work of spraying for prevention. 

 It determines the time of spraying and the strength 

 of solution that may be used with success. 



Spraying for prevention. 



Spraying for the prevention of plant diseases 

 has now become a fixed practice in the better agri- 

 cultural regions throughout the world. It owes its 

 existence to the simple fact that many of the special 

 diseases which attack farm, garden and orchard 

 crops are infectious by nature, and spread from 

 plant to plant by means of small seed-like struc- 

 tures, called spores, which may be readily borne by 

 Ihe winds, water, insects or other agencies. When 

 they fall on the growing plant, they begin to grow 

 either by attacking the plant surface or by send- 

 ing filaments into the internal structures. It has 

 been found that certain solutions, applied at the 

 proper time, cut short the lives of these spores and 

 their developing growths, preventing injury to the 

 plant on which they fall, or on which they are 

 spreading. The aim of spraying is to cover all 

 surfaces that are likely to be attacked, or on which 

 spores are likely to fall, with a film of some chem- 

 ical, either dry or in solution, that will prevent the 

 germination of the spores and the development of 

 the disease-producing organisms, and, at the same 

 time, not injure the foliage and living tissues of 

 the plant on which the spray falls. It is thus 

 merely a matter of disinfection. 



The time for spraying can be properly deter- 

 mined only by a close observation of the period 

 at which the. disease is spreading and by con- 



