DISEASES OF CULTIVATED PLANTS 655 



With the white onions the problem is partly a field problem at 

 harvest time, and partly one of storage. The growers are in the 

 habit of gathering the white onions before the tops fall, and top- 

 ping them immediately, instead of throwing together in heaps for 

 absorption of the substance of the tops by the onion bulbs as is 

 practiced with the riper red and yellow varieties. After topping 

 the white onions are placed in slatted crates, and these crates are 

 stacked in the field or in open sheds where they are kept dry. Often 

 the loss from rot during the six weeks following harvest may reach 

 60 per cent of the crop and as shown by investigations in Connecticut 

 and our own state, it has not always been clear why these losses are 

 so large. Recent investigations by this department lead us to believe 

 that the green onion neck of white onions handled in this way affords 

 entrance for the organism of the rot. 



The sclerotium rot (Sclerotium cepivorum) appears to be the 

 most serious, although smudge or anthracnose of the onion ( Vermi- 

 cularia circinans) may sometimes cause large losses. Both these rots 

 are described under diseases of the onion. The writer believes the 

 Sclerotium rot is the larger criminal, and that both may be handled 

 by disinfection of the onions immediately after harvest. This dis- 

 infection may be carried out as described under the Maine formula 

 for Formaldehyde Gas Treatment, which is : 



Commercial 40 per cent Formaldehyde 3 pounds. 



Potassium Permanganate crystals 23 ounces. 



Sufficient for 1,000 cu. ft. of space occupied by crates or trays. 



The object of immediate disinfection is to prevent the entrance 

 of these organisms, particularly the sclerotium rot, through the green 

 neck of the newly topped onions. The exuding juices offer favor- 

 able culture conditions for the fungus to develop. 



When no fumigation is practiced following harvest, the onions 

 which are found to be sound and delivered for storage at the close of 

 the season may very profitably be treated in this way before winter 

 storage. Both these rots are essentially dry-rots of onions. In addi- 

 tion, sometimes, we have wet-rot of white onions which may be 

 either due to bacteria or to the same fungus <as the wet-rot of Globe 

 or other onions mentioned below. 



The rots of yellow and red onions are of both the wet-rot and 

 dry-rot types, but the wet-rots are much more serious with these 

 varieties. Doubtless, as in all vegetables held for a long time in 

 storage, we have many cases of wet-rot in onions where some of the 

 common decay bacteria are the chief cause. These find entrance 

 through wounds, as in topping, and, under conditions favorable for 

 their development invade the tissues of the onion and cause decay. 



In addition, however, to the wet-rots due to bacteria of unde- 

 termined species, we have a specific wet-rot of onions due to Fusar- 

 ium species. This wet-rot fungus belongs to the same group as the 

 potato dry-rot and is liable to infect soils in which onions are grown 

 year after year. Rotted onions will show external developments of 

 the pink fungus and may be detected in that way as well as by use 



