yio Journal of Agricultural Research voi.xx.No.o 



infections on the necks which were so conspicuous in 191 5 were almost 

 entirely absent. 



To summarize, the disease progressed most rapidly during the last 

 part of the growing season of 191 5, with the mean temperature range 

 between 20 and 30 C, accompanied by sufficient rainfall to promote 

 abundant spore production and dissemination as well as subsequent 

 infection. On the other hand, development was materially checked in 

 1 91 6 by extreme heat, together with lack of precipitation during July. 



RELATION OF ENVIRONMENT DURING CURING TO THE DISEASE 



The onion set crop is usually harvested in early August. The tops 

 are twisted or clipped and the small bulbs are placed in shallow crates 2 

 or 3 inches deep. These are stacked in the field in piles with temporary 

 roofs, where they are allowed to cure for several weeks. Usually the 

 fungus is well established upon the outer scales of the bulbs before they 

 are pulled, and thus further invasion is dependent largely upon the 

 environmental conditions which prevail during the curing and storage 

 periods. 



The respiratory functions of the living cells in the bulbs continue after 

 the sets are pulled, and there is, in consequence, some accumulation of 

 moisture. This is counteracted in part by the use of shallow crates 

 which are exposed to natural air currents. In bright, windy weather 

 the bulbs cure rapidly, while rainy or humid weather retards the process 

 and favors the progress of the disease. A number of experiments were 

 conducted during 191 6, 191 7, and 191 8 to determine the effect of varied 

 amounts of external moisture during the curing period upon the develop- 

 ment of the disease. 



Experiment 1. — On August 15, 191 6. a crate of white sets was taken 

 from the general run of the crop which had been harvested on August 9 

 at Racine, Wis. The outer scales were badly spotted with smudge, and 

 in some cases the second scale had been invaded. After removal to the 

 laboratory the bulbs were sprinkled with water while in the crates. 

 After two days a portion of this lot (5^ pounds) was dried for 24 hours at 

 45 to 52 C. and the remainder (14K pounds) was given no further 

 treatment. Both lots were placed under cover in a shallow crate, where 

 they were exposed to good conditions for further natural curing. They 

 were later placed in a well-ventilated onion warehouse held at about 

 35 to 40 F. On January 13, 191 7, both lots were examined. Most 

 of the outer dead scales present at harvest time had sloughed off during 

 storage, and in the dried sets the fungus had advanced very little from 

 these original infections. In the naturally cured sets, however, the 

 fungus, probably aided by the greater excess of moisture present, had 

 invaded several underlying scales, and these sets were badly spotted 

 even after the outer scales were removed. The sets in each lot were 

 then sorted into three classes — (1) free from disease, (2) slightly diseased, 



