DISEASES OF CULTIVATED PLANTS 559 



of their stock under conditions which preclude a knowledge of the 

 amount of disease which appeared on the fields where the stock was 

 grown. In such cases a special disinfecting room should be provided 

 and fitted up with provisions made for the proper regulation of the 

 temperature and moisture conditions during treatment. This work 

 should be placed in the hands of a competent man who thoroughly 

 understands each step and -detail of the process. All seed tubers 

 which are not known to be free from the germs of blackleg and 

 potato scab should be disinfected in this way before being shipped. 

 (Me. E. S. B. 194.) 



Early Blight of Potato. It may be readily recognized and easily 

 distinguished from the Late Blight and the other potato diseases. 

 Early Blight begins to show itself about the time that the blossoms 

 appear. More rarely it attacks plants scarcely six inches high. The 

 first indications are relatively small grayish-brown spots, which, as 

 they become larger, are marked with faint concentric circles, giving 

 a target-like appearance to them. The spots may increase in size till 

 several of them run together and form large patches of dead tissue. 

 In the course of a few days these spots become brown and withered, 

 while the rest of the leaf takes on a yellowish, sickly color, though 

 the stems may remain green. Sometimes the disease progresses 

 quite slowly and the vitality of the plant is only gradually reduced. 

 In any case, however, the tubers either stop growing entirely or re- 

 main so small as to make them of little value. The death of the 

 vines in this way is often mistaken for early ripening and it then 

 occasions a surprise to find that no tubers of value are present. 



Any injury to the foliage, such as insect bites or bruises from 

 hail, seems to furnish the condition for the entrance of the fungus 

 into the leaf. Likewise any decline in the vigor of the plant seems 

 to invite attack. Drought, poor soil, delayed development due to 

 cold weather, excessive heat tending towards wilting or sun-scald, 

 all make the plants less able to withstand the attacks of this blight. 

 In other words, the more nearly perfect the plant and the more vig- 

 orous its growth the less likely it is to suffer from this parasite. 

 (Wyo. E. S. B. 71.) 



Satisfactory treatment for this disease has not yet been found. 

 Many experiments, however, have shown that the effects of the dis- 

 ease may be greatly reduced by two or three thorough sprayings 

 with Bordeaux mixture. The spraying must be thoroughly done and 

 the first application must be made previous to the appearance of the 

 blight. After the leaves have become filled with the mycelium and 

 the spots are beginning to show it is too late. Prevention must be 

 the aim, and this is accomplished by putting the leaves in such a 

 condition by the application of the Bordeaux that the spores cannot 

 germinate upon the leaf surface. For further directions, see tho 

 subject of spraying at the close of this bulletin. 



Late Blight of Potato. During the time that the fungus is 

 spreading its mycelium through the tissues of the leaf there is little 

 to indicate its presence. When the fruiting stage is reached it .^oon 

 becomes evident enough by the formation of brown spots, which. 



