SPRAYING AND DUSTING ONIONS 183 



spraying and dusting with copper fungicides, for the prevention of this disease. 

 But downy mildew does not cause loss in Massachusetts often enough or seriously 

 enough to warrant sprajdng onions every year, unless it can be shown that in- 

 creased yields would much more than pay for the cost of spraying in years when 

 there is no downy mildew, and especially in years when blast occurs. We are now 

 in a position to comment further on the effects of copper fungicides on onions 

 under the conditions indicated above. 



Copper-lime dust as used, resulted in injury to onions sufficient to more 

 than offset any possible fungicidal value. In no year was it of any real or consis- 

 tent benefit, and in two years, including a year of blast, it was definitely injurious 

 and much more injurious than the same number of applications of Bordeaux 

 mixture. Yields of onions in a year of blast were increased by Bordeaux mixture, 

 but not by copper-lime dust. In this response, blast of onions again showed some 

 similarity to tip-burn of potato, for in the experiments of Butler (5) copper-lime 

 dust was much inferior to Bordeaux mixture in reducing injury of potatoes due 

 to tip-burn. 



Onions were not injured by Bordeaux mixture 4:4:50 or even 8:4:50 applied 

 with suitable machinery at a pressure of 100 to 150 pounds, although it was in- 

 jurious when applied by hand and in too large amounts at a pressure of 200 

 pounds. With the object of reducing the total cost of appUcations, Bordeaux 

 mixture 8:4:50 was applied only half as often as was Bordeaux mixture 4:4:50. 

 In the absence of blast, yields were increased about as much by Bordeaux 8:4:50 

 applied at intervals of two weeks as by Bordeaux mixture 4 :4 :50 applied weekly, 

 and at less cost. Neither treatment, however, gave significantly increased yields 

 with enough consistency to prove that spraying onions with a copper fungicide 

 would be a profitable operation in years of no blast and no downy mildew. In a 

 year of blast (1931), yields were increased more by Bordeaux mixture 4:4:50 

 applied weekly than by Bordeaux mixture 8:4:50 applied at intervals of two 

 weeks. 



Bordeaux mixture of both concentrations delayed the onset of blast, as it is 

 known to delay the appearance of tip-burn of potato. Four weekly applications 

 of Bordeaux mixture 4:4:50, begun July 27, just before blast occurred, were 

 followed by the largest and most consistent increases in yield, and this is the 

 concentration and schedule preferred should a grower wish to attempt protection 

 against blast by spraying. Blast occurred in only one year out of the three in 

 which these experiments were conducted and the increases in yield which re- 

 sulted from this treatment were not, in our opinion, great enough to warrant 

 the recommendation that onions be sprayed every year for protection against 

 blast. 



Increases in yield following the use of milk of lime were even smaller, and 

 Bordeaux mixture is certainly to be preferred to it. But in a year of blast, yields 

 were increased a little by milk of lime, this increase (for the mean) being greater 

 than in years of no blast. 



It has been established (3) that, in spite of certain practical difficulties in- 

 volved, onions may be successfully protected against thrips by spraying two or 

 three times in a season with a nicotine sulfate-fish-oil soap combination. But a 

 satisfactory power sprayer for such a crop is relatively expensive and onions 

 have not often been sprayed in the past to prevent injury by thrips. Growers 

 who, individually or jointly, find the ownership of a power sprayer feasible, and 

 who spray onions for protection against thrips may, on the basis of the results 

 of our experiments, expect some further increase in yield if Bordeaux mixture 

 4:4:50 is used with nicotine sulfate. But the data as presented above do not 



