POTATO BLIGHTS OR '' RUSTS " I05 



by spores. Fig. 37 shows the curiously shaped spores of the 

 ■early blight germinating preparatory to infecting the host 

 plant. Fig. 35 shows the egg-shaped spores of the late blight. 



Repeated experiments have shown that both these diseases 

 may be profitably controlled by spraying with the Bordeaux 

 mixture. 



When to Spray. — For early blight on early potatoes, spray 

 when the vines are about two thirds grown or as soon as the 

 disease makes its appearance ; repeat the spraying in about 

 two weeks. 



For both early and late blight on late potatoes spray three 

 times ; the middle of July, the first of August, and the middle 

 of August. 



Rainv weather may render it advisable to spray at shorter 

 intervals and to increase the number of sprayings. 



Spraying Outjit. — Fig. 36 shows a convenient outfit for po- 

 tatoes or fruit trees ; a pump specially designed for spraying 

 mounted on a barrel of about ^o gallons capacity drawn on a 

 wagon with one man to pump and another to apply the spray. 

 In spraying potatoes a liberal length of hose should be used ; 

 we use fifty feet or more. A farmer naturally hesitates to drive 

 over a tield of thrifty " tops," but the injury is hardly to be 

 considered as against the benefit of spraying. With a good 

 lensfth of hose the necessitv of drivinof over the field is reduced 

 to a minimum. 



Effect of Bordeaux Mixture on Insect htjuries. — In this 

 regard the following is of interest. A field was sprayed three 

 times with Bordeaux mixture, a strip across the rows on one 

 side was left unsprayed as a check. Between the first and 

 second sprayings the unsprayed vines died. No fungous 

 trouble could be detected, nor were the "-slugs" of the Colo- 

 rado beetle present, although many of the mature beetles were. 

 The flea beetle., however, was present and was probably the 

 chief cause of the destruction of the vines. The sprayed vines 

 lived. A strip of the sprayed potatoes of the same area as the 

 unsprayed and lying next to it yielded a little more than three 

 times as many marketable potatoes. Bordeaux mixture is 

 probably one of the best remedies against the flea beetle. (See 

 Bulletin 29 of this Station.) 



