40 MASS. EXPERIMENT STATION BULLETIN 327 



suspension, wetting and spreading power, injury to plant, and weight of corms 

 produced. While the results cannot be accepted without reservation, due to 

 the fact that the materials were applied to assorted varieties, they indicate 

 that all of these treatments reduced the average weight per corm as compared 

 with the unsprayed checks. Inasmuch as the infestation of thrips in these plots 

 was light, the factor of thrips injury can be dismissed in this comparison. 



Ol the various contact poisons that were used, including Black Leaf 40, 

 pyrethrum, derris (two brands) and aliphatic thiocyanates (Lethane 420), 

 derris and Letnane seemed to be superior to the others and were approximately 

 equal in killing value. 



2. Varietal differences in susceptibility to thrips attack. Several authors 

 have noted more or less difference in thrips injury to different varieties of 

 gladiolus. One theory holds that the color of the plant masks the injury; an- 

 other, that some difference in the plant itself favors the development of a large 

 number of thrips. 



Observations were made on a large number of varieties. Damage to leaves, 

 buds and flowers was noted. The population was noted by counting the 

 number of thrips in the buds. The heaviest damage occurred to a purple 

 variety and the lightest to a white. Data would indicate, however, that the 

 color has little to do with the abundance of thrips. One pink variety was noted 

 to have an average population of 8.5 thrips per bud, whereas another similar 

 pink had an average of 55.3 thrips per bud. 



Further evidence was secured during the summer that in Massachusetts the 

 gladiolus thrips overwinters only on corms. Gladiolus fields immediately ad- 

 jacent to areas where gladiolus had been grown the previous year and seriously 

 damaged by thrips, showed no serious infestation at the time the fields were 

 visited in mid-August. These fields showed only a very light and scattering 

 infestation and no commercial damage. In all cases the corms had been treated 

 during the winter of 1934-35. 



Substitutes for Lime-sulfur in Summer Sprays for Orchards. These tests were 

 continued in cooperation with the Department of Pomology. The studies were 

 chiefly confined to a combination of 300-mesh sulfur and wetting agent; a 

 combination of dry lime-sulfur and flotation, each used at half strength; 

 various strengths of dry lime-sulfur; and Kolofog with a colloidal spreader and 

 lime to prevent the blotching of fruit and to overcome the extreme persistence 

 characteristic of that material. These were used in the calyx and four cover 

 sprays following. Lead arsenate was used in all tests: 4 lbs. per 100 gals, in 

 the calyx, 1st and 2d cover sprays; 3 lbs. per 100 gals, in the 3d cover spray; 

 and 2 lbs. per 100 gals, in the 4th cover. 



No injury to foliage nor russeting of fruit was noted following any combina- 

 tion of wettable sulfur or of 300-mesh sulfur and wetting agent. Dry lime- 

 sulfur at the higher strengths caused slight burn to foliage of Baldwin, Green- 

 ing, and King and a faint trace on Mcintosh leaves. Mcintosh fruit also 

 showed a slight amount of russeting. No record was made of the Baldwin 

 crop since it was too light and uneven. The degree of control from the use of 

 these sprays was measured on Mcintosh. Results are as follows: 



