656 INSECTS AFFECTING VEGETATION 



of the microscope. The chief factors of control with onions of this 

 kind, are in the methods of culture followed to produce the crop. 



Dry-rot of red and yellow onions is rather rare and is commonly 

 referable to the anthracnose or Vermicularia dry-rot fungus described 

 under white onions. The best temperatures for onion storage are 

 about 38 to 42 degrees. (Ohio E. S. B. 214.) 



INSECT CONTROL MEASURES. 



REMEDIES FOR PLANT DISEASES FUNGICIDES. 



In no other line of applied science has America made more rapid 

 progress than in the matter of plant disease remedies. While the 

 general doctrine of parasitism and the transmission of parasitic dis- 

 eases are thoroughly investigated and widely published in Europe, 

 the application of remedies and the interest in disease prevention 

 fall much behind the practices in America. Possibly this great 

 progress is due to the greater readiness with which Americans en- 

 gaged in crop production, accept the teachings of scientists and make 

 practical applications of the results obtained. Among remedies for 

 plant diseases we must include all treatments which tend to restrict 

 or prevent the recurrence of diseases, that is, all treatments which 

 remedy infections or limit the spread of parasitic attack. 



Seed and Soil Treatment. In the seed treatments high tempera- 

 tures, as in the hot water, or the application of a germicide as in 

 solutions of formaldehyde are applied to the seed grain to destroy 

 adhering spores. In the treatment of tubers and roots as the potato, 

 etc., longer soakings with solution of formaldehyde or corrosive sub- 

 limate are required to kill not only external spores but resting forms 

 of fungi such as sclerotia, etc. 



With soil treatments we have the problem of killing out soil 

 infesting organisms such as nematodes or eelworms and Rhizoctonia, 

 Botrytis, lettuce drop, etc., among the fungi. All these results are 

 obtained by thoroughly steaming the soil. In a measure the same 

 results are also obtained from a formaldehyde drench as elsewhere 

 described. 



Fumigation for the destruction of seed infesting fungi or cut- 

 ting infesting insects is of the same character and must be named 

 here. The fumigation of nursery cuttings with hydro-cyanic gas is 

 effective as is also the fumigation of stored grain with carbon bisulfid. 

 We must also consider that wound coverings are methods of preven- 

 tion in plant disease, since these coverings of asphaltum creosote, 

 gas tar, paraffine and even of paint serve 'the purpose of excluding 

 wound fungi which might otherwise cause serious decays. All these 

 treatments that have just been enumerated apply to the treatment of 

 the soil or of seeds and plants in resting condition. The great prob- 

 lem of keeping down infection during the growing period yet re- 

 mains for the application of spray mixtures. (Ohio E. S. B. 214.) 



HOW TO OBTAIN SUCCESS IN SPRAYING. 



Success in spraying is to be secured only by careful attention to 

 details in two principal directions: (1) Sprayings must be timely, 

 and the proper time varies with the particular conditions. The oper- 



