38 MASS. EXPERIMENT STATION BULLETIN 449 



3d and 25th. Cold weather somewhat retarded the first appearance of the plants, 

 but once they broke ground they made steady and satisfactory growth. June 

 also was slightly cooler and rainfall slightly less than usual. Growth was some- 

 what slow but was not seriously interrupted. The balance of the growing season 

 was warm and very dry. The location of the experimental plots in rather a low 

 area and on heavy soil prevented serious retardation, and the plants progressed 

 very well and matured a good crop. 



No spray injury was noted at any time during the season except a possible 

 trace following calcium arsenate. The plants showed a tendency to ripen slightly 

 earlier than usual but many were alive until the heavy killing frost in late Sep- 

 tember. This was very noticeable on the DDT plots, which remained green 

 right up to frost. 



Early flea beetle attack was comparatively negligible, but by late July the 

 second brood appeared in some size and continued to mid-August. A moderate 

 infestation of plant lice appeared in early August. Aphids were in moderate 

 abundance through all plots except those given DDT emulsion, where only a 

 few appeared. 



Fifteen applications were made at weekly intervals from June 12 to September 

 17 to protect all new growth from attack. At least three extra applications were 

 made to furnish protection in case of the recurrence of blight, which caused such 

 havoc to tomatoes and potatoes in 1946. By mid- August the plants in the 

 Bordeaux-sprayed plots began to show less vigor and considerable scarring from 

 flea beetle attack. Where calcium arsenate was added, somewhat less flea beetle 

 damage was noted, but there was a light amount of spray injury. The plots 

 receiving DDT were of superior appearance, upright, vigorous, and remarkably 

 free from any trace of insects. 



The contrast between the DDT plots and the other plots grew more noticeable 

 as the season advanced. Examination of growing tips from the different plots 

 indicated the protection furnished by DDT. Samples from the Bordeaux plots 

 showed 4560 perforations per 10 tips, while similar samples from the DDT 

 (wettable powder) plot showed only 264 feeding punctures and from the DDT 

 (emulsion) plot, 220; and superficial examination of the plants in the latter plots 

 failed to indicate any damage. 



Yields were high in both plots spraj'ed with DDT. The highest yield was 

 slightly over 466 bushels per acre in the plot where the DDT emulsion was ap- 

 plied. The yield in the DDT (wettable powder) plot was 96 bushels per acre 

 (or 30 percent) greater than in the adjoining Bordeaux plot; and where the DDT 

 emulsion was applied, the increase in yield was 148 bushels per acre or 46.5 

 percent greater than where Bordeaux alone was used. 



Control of Onion Thrips. (A. I. Bourne.) Onion sets were preferred to seed 

 onions because the cold, wet spring season prevented early preparation of the 

 plot and sets would furnish material for tests much earlier than would seed onions. 



Thrips infestation developed slowly after a somewhat late appearance. A 

 very few were found by the third week of June, and hot dry weather in July 

 promoted rapid increase. Throughout the Valley, the prevailing weather condi- 

 tions delayed thrips development so that many of the fields of set onions were 

 pulled before thrips had reached very great numbers. Some of the plantings of 

 seed onions, maturing later in the summer following the hot dry weather of July 

 and August, showed moderately heavy attack. 



The first application of insecticides was on July 15 when the plants averaged 

 15 to 16 inches in height and had an average of about 30 thrips per plant, a com- 

 paratively light infestation. 



