66 MASS. EXPERIMENT STATION BULLETIN 347 



Control of Plum Curculio in Apples. (W. D. Whitcomb, Waltham.) In 1937 

 the emergence of plum curculio beetles from hibernation was later than normal 

 and only 2 percent of them were in the trees when the calyx spray was applied 

 to Gravenstein and Mcintosh on May 19. By May 24, when Baldwin and Wealthy 

 received the calyx spray, the number of beetles in the trees had increased to 11 

 percent, and jumped to 32 percent on May 29. 



Due to the acute scab situation at that time, an early calyx application was 

 advisable. On Mcintosh, lead aresenate could have been safely omitted from the 

 calyx spray but on the more rapidly growing varieties such as Gravenstein, 

 Duchess, Transparent, and Baldwin, it was necessary for the best curculio control. 



The critical period in curculio activity extended from May 25 to June 2 with 

 the maximum injury- occurring from May 30 to June 1. 



In the experimental orchard, which was heavily infested with curculio, studies 

 were begun to determine whether the size of apples during the critical period 

 influenced the control by spraying. Gravenstein apples sprayed with lead arsenate 

 at the rate of 4 pounds in 100 gallons on May 25, when the average diameter of 

 the fruit was 5.04 sixteenths of an inch, had 54.24 percent of the fruit stung. 

 Mcintosh which measured 3.94 sixteenths of an inch in diameter when sprayed on 

 May 30 had only 16.14 percent of the fruit stung. Wealthy and Baldwin apples 

 measuring 4.20 and 4.26 sixteenths of an inch when sprayed on May 30 and May 

 28 showed 18.83 percent and 16.38 percent stung fruit respectively. These pre- 

 liminary experiments showed that the apples (Gravenstein) which measured 

 approximately 5/16 inch in diameter when sprayed suffered about three times as 

 much curculio injury as those apples (Baldwin, Wealthy, Mcintosh) which were 

 approximately 4/16 inch in diameter when sprayed. 



Biology and Control of Carrot Rust Fly. (W. D. Whitcomb, Waltham.) The 

 field infestation by the carrot rust fly was moderately light at Waltham in 1937, 

 and the untreated carrots showed 14 percent commercial injury by the first 

 generation. Some injury to celery was reported by market gardeners but this 

 pest was not one of major importance this season. 



Treatment of the seed at planting with pure calomel powder gave 99 percent 

 protection, again demonstrating that this is a practical treatment for early 

 carrots exposed to a light infestation. When the calomel was mixed with equal 

 parts of clay as a seed treatment, 4 percent of the carrots were commercially in- 

 jured; but when the seed was treated with a 1-3 mixture of calomel and clay the 

 carrots showed as much injury as the untreated planting. The addition of pow- 

 dered gum to the calomel failed to increase the adhesion of the calomel to the seed 

 and gave unsatisfactory results. 



Four applications (June 5, 12, 19, and 26) of cube-clay dust to carrots from 

 seed sown May 4 gave complete protection from this insect, and can be rec- 

 ommended. 



Adaptability of Cryptolaemus to Control of Mealybugs in the Greenhouse. 



(W. D. Whitcomb and William Garland, Waltham.) Studies of the development 

 and activity of Cryptolaemus montrouzieri at controlled constant temperatures of 

 60°, 70°, and 80° F. were continued. In the 1937 studies this insect was stimulated 

 at 80° considerably more than in previous observations, although the results 

 again indicated that 80° is slightly excessive and that 70° is nearer the optimum. 



