ANNUAL REPORT, 1938 15 



or more. Frequently either carelessness or poor farm management was respon- 

 sible for sheet erosion. Wind erosion was found mainly in the Connecticut 

 River Valley and the Cape Cod section. Flood erosion of the more devastating 

 nature was found along the Connecticut, Merrimack, Blackstone, and Housa- 

 tonic rivers. 



Soil erosion within the State can be easih- controlled if measures are taken to 

 help the individual farmer to overcome his particular soil erosion trouble. The 

 correct and more extensive use of cover crops, proper rotations with sod, strip 

 farming, and contour cultivation would aid greatly, where feasible, in totally 

 eliminating any soil erosion. 



This investigation was carried out in cooperation with the Soil Conservation 

 Service of the United States Department of Agriculture. A more detailed report 

 has been submitted to the cooperating agencies in Washington. 



Onion Blast. (W. G. Colby.) The onion disease known as blast occurs fre- 

 quently in the Connecticut Valley. It is specifically a disease of the tops of 

 onions, but has a marked consequent effect on the yields and quality of bulbs. 



The onions in the Valley have been affected severely by blast during the last 

 two seasons. In 1938 only seed onions were much affected; in 1937, however, 

 the disease developed considerably earlier than in 1938 and caused serious injury 

 to the tops of set onions as well as an early, premature dying of the tops of seed 

 onions. The yields of set onions were much reduced by the attack of blast in 

 1937, and much of the loss caused by rot, both at time of harvest and subse- 

 quently in storage, seemed to be directly attributable to the deleterious effects 

 of the blast on the growth and formation of the bulbs. The yields of seed onions 

 were greatly reduced by the smallness of the bulbs produced as a result of the pre- 

 mature death of the tops. 



The cause of blast has been the object of many field observations and experi- 

 mental trials by research workers at this station for more than ten years. In 1931 

 Jones (Annual Report, Mass. Agr. Expt. Sta. Bui. No. 271, p. 243) reported from 

 greenhouse experiments that an injury resembling blast could be induced by sub- 

 jecting plants to reduced light, high relative humidity, and a wet soil for a period 

 of ten days and then exposing them for a few hours to intense sunshine and an 

 atmosphere of low relative humidity. Later in the same year, Doran and Bourne 

 (Mass. Agr. Expt. Sta. Bui. 279), as a result of many field observations and trials, 

 expressed the opinion that, "These and other considerations indicate ... a physiol- 

 ogical rather than a parasitic cause of onion blast." The writer, too, after making 

 careful field observations during the severe "blast years" of 1937 and 1938, 

 reached essentially the same conclusions. The opinions expressed here are for 

 the most part elaborations of ideas previously expressed. 



The environmental conditions producing blast were so typical in 1938 and 

 the resulting blast so severe, that it was thought desirable to report in detail the 

 manner in which the trouble developed. During the month of June, over 8 

 inches of rain fell and the mean daily temperature was slightly above normal. 

 Onions, both from sets and from seed, made a vigorous, healthy, dark-green top 

 growth and gave excellent promise of a bumper yield until about June 21. A 

 week of cloudy, rainy weather from June 11 to June 18 was followed by hot, clear 

 weather which began June 19 and continued until June 26. Blast symptoms 

 first appeared about June 21 on onion seed sets and on seed onions planted on 

 light soil. The blast began on the lighter soils along the river banks and spread 

 back toward higher terraces. Seed sets and seed onions on other light soil areas 

 blasted at this time also. Blast was first characterized this year, as usual, by the 

 appearance of small white spots on the leaves, followed by a dying back from the 

 leaf tips. 



