10 



full life history of the organism causing the trouble. He should 

 know where the organism spends its time when not on the 

 plant in question. It frequently happens that diseases may be 

 introduced into new localities on the seed. A marked case of 

 this kind was encountered in eastern Virginia in the spring of 

 1911. A large grower of plants purchased cabbage seed from 

 a certain seed concern and planted them for the purpose of 

 growing plants for his neighbors. He supplied about two mil- 

 lion plants to the different truckers. Within a few weeks 

 ploma wilt appeared in all the fields where plants from this 

 particular lot were used, the loss resulting in from 50 per cent 

 to 90 per cent of the crop. The man who grew the plants was 

 guilty of negligence, and the man who used them was innocent; 

 but if the plant grower had followed the instruction given by 

 the experiment station, the disease need not have been intro- 

 duced. 



Some diseases may be controlled by soil treatments. That is, 

 the soil may be rendered favorable or unfavorable for their 

 development by the treatment given it. This is especially 

 true with some forms of bacterial and fungous diseases. In 

 other instances, the disease may be controlled by treating the 

 seeds or the vegetative portion of the plants used for propa- 

 gation. 



The Virginia Truck Experiment Station in co-operation with 

 the Maine Experiment Station has been conducting a series 

 of investigations looking to the control and eradication of 

 the " black-leg " disease formerly prevalent in some potatoes 

 brought from the north and planted in the south. This work 

 has resulted in developing practical means of eliminating the 

 trouble by selection of the seed potatoes in the fields in the 

 north. 



At the present time the preventive measures are much more 

 important than are the curative. Blight can be controlled in the 

 potatoes by spraying with fungicides before the disease makes 

 its appearance, but if once established in the plants, the problem 

 of eradicating it is quite difficult. 



The experiment stations frequently outline modifications in 

 methods of culture that will largely control a number of the 

 more malignant diseases. 



