Plant Diseases 



425 



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/«. F. Pooie. A?^. J. Expt. Sta. 



Fig. 263. Bean seeds affected by anthracnose. The principal means 

 of controlling the disease is to reject all seeds for planting that show 

 the characteristic reddish spots. 



recently the lime-sulfur sprays have been found an efficient pre- 

 ventive of certain diseases. All sprays are directed toward 

 killing of the parasites before they invade the host tissue. 



Another method of disease control is exemplified by the removal 

 of all common barberry bushes, now being extensively carried on 

 in the Northern wheat-growing states to decrease the losses from 

 stem rust of wheat. In the Northern states also attempts are 

 being made to check the ravages of the white-pine blister rust 

 by removing the wild currants and gooseberries which form the 

 alternate host of the pine-rust fungus. The removal of red- 

 cedar trees from the vicinity of an orchard will prevent apple rust. 



The development of disease-resistant varieties of crop plants 

 is a third method of control that has been successfully used. The 

 Kanred wheat is highly resistant to rust. A strain of cabbage 

 has been selected that is resistant to cabbage yellows. New 

 immune varieties of watermelon, tomato, and cotton have in 

 certain sections replaced the older varieties which were suscep- 

 tible to " wilt " diseases. 



