VEGETABLE AND FIELD CROPS 273 



threads (sclerotia), varying in size from a pinhead to a grain 

 of wheat. They are seen clearly only when the tuber is wet. 



Soon after planting the young sprouts are attacked by 

 this waiting fungus. Black spots appear near the surface of 

 the ground, destroying the bark and often girdling the stem. 

 A dark network of fungous threads is sometimes seen upon 

 the subterranean parts. This advances above ground and 

 develops a gray spore-bearing layer about the green stem, 

 often extending upward several centimeters, causing the 

 young shoots to wilt, droop, and die. Often a loss of one 

 fourth to one third of the plants follows. Those stems 

 which survive this early attack, but which are attacked later, 

 show the aerial tubers mentioned above and produce a few 

 underground tubers ; and these small and unsalable. Such 

 tops may develop peculiar twisted leaves with prominent 

 veins and bear their leaves in a crowded manner that enables 

 their easy recognition, even from some distance. If these 

 plants be examined closely, the injury caused by the fungus 

 will frequently be found as a wound often 2-3 cm. long 

 upon the stem at or near the surface of the ground. 



In some of these symptoms this disease closely resembles 

 the bacterial malady known as " blackleg," which is de- 

 scribed upon a later page. Fortunately the remedial meas- 

 ures are similar. 



Only clean seed should be used. If there is any doubt as 

 to freedom of the seed from the disease, it should be treated 

 as is recommended for potato scab. Liming the soil, clean 

 culture methods, and crop rotation are preventive. Infected 

 refuse should be destroyed by fire. Soil badly infested 

 should not be planted in potatoes. In general the remarks 

 made under soil diseases apply here. 



