Part II.] POTATO DISEASES. 131 



Dry Rot and Wilt. — This disease, caused by a fungus (Fusa- 

 rium), attacks both tubers and stems. In the tuber it causes brown 

 discoloration of the so-called bundle ring just beneath the surface. 

 This is easily seen when an infected tuber is cut crosswise at the 

 stem end (Fig. 8). In storage the fungus may cause a dry, pow- 

 dery rotting of the entire interior of the tuber. The disease spreads 



Fig. 8. — Dry rot, showing discolored bundle ring at stem end of tubers. (After 

 Bulletin No. 55, Bureau Plant Industry, United States Department of Agri- 

 culture.) 



upward from infected seed tubers into the stems, causing them to 

 turn yellow, wilt and die prematurely. Often diseased plants may 

 be detected before wilting by their stunted, yellow appearance. 



Control. — Discard all seed tubers which show discoloration of 

 the bundle ring at the stem end. Do not plant for five years on 

 land where the disease has occurred. 



Sprays. 



Potatoes are sprayed principally for the control of early and late 

 blights and for insect pests. The following schedule is adapted to 

 Massachusetts conditions : — 



First Spray. — When the plants are about 6 inches high, use 

 Bordeaux mixture (4-4-50 formula), to which should be added 

 3 to 6 pounds of lead arsenate paste or 2 to 3| pounds of lead 

 arsenate powder for each 50 gallons. 



Second Spray. — Ten days to two weeks after the first applica- 

 tion, using the same mixture. 



Subsequent Sprays. — The crop should be sprayed with sufficient 

 frequency to keep the vines well covered with spray material. In 

 wet seasons this may mean as often as every ten days, but ordina- 



