ANNUAL REPORT, 1938 59 



•90 percent salable heads. Applications to the roots at the time of transplanting, 

 using pure calomel powder and calomel-talc mixtures containing 75, 50, and 

 25 percent calomel, all gave about 90 percent protection. Mixtures containing 

 10 and 5 percent calomel were not effective. Actually, the 75 percent calomel-talc 

 powder gave the greatest protection, but the advantage over the 50 percent mix- 

 ture was so littleihat the latter seems more practical. Both the 75 and the 50 

 percent calomel-talc mixRi/es gave slightly more protection than pure calomel, 

 apparently because of the better adhesiveness of the talc. Plants treated with 

 pure calomel wilted considerably when first transplanted but recovered quickh- 

 after root growth was stimulated by rain. 



Maggot injury to plants which received root treatment when transplanted was 

 confined almost entirely to the upper part of the root which grew after the treat- 

 ment was applied. This type of injury is much less destructive than when the 

 feeding roots are eaten, and seldom checks the growth of the head severely. 



Cabbage Maggot in Radishes. (\V. D. Whitcomb, Waltham.) Radish seeds 

 were planted at approximately 10-day intervals from May 2 to August 15. One 

 lot of seed was untreated and one lot received the calomel seed treatment at the 

 rate of Yi pound of calomel powder on each pound of seed. Approximately one 

 month after the seed was sown, 100 radishes selected at random were examined 

 and the injury by cabbage maggot classified. Appreciable injury, making more 

 than 15 percent of the radishes unmarketable, was found only in the May 2 and 

 12 plantings and again in the June 14 and 22 and July 2 plantings. 



Calomel seed treatment and weekly applications of a .6 percent rotenone dust 

 in the latter part of the season failed to protect the radishes, and no effective 

 economical control of this insect on radishes was secured. These experiments 

 indicate, however, that radishes can be grown profitably if the seed is sown so as 

 to avoid the periods of maggot activity as shown above. 



Control of Striped Cucumber Beetle on Cucumbers and Melons. (W. D. 



Whitcomb, Waltham.) In 1938, striped cucumber beetles were extremely abund- 

 ant and in the experimental planting 3773 beetles were recorded compared to 

 685 beetles in 1937. In these plantings, which contained an equal number of 

 cantaloupes, melons, and cucumbers, 65 percent of the beetles were found on the 

 cucumbers indicating a decided preference for that plant. 



The results in the experiment are somewhat handicapped by an unusual and 

 unexpected migration of beetles from near-by plantings of cucurbits. This was 

 especially noticeable in July when hills of cucumbers and melons which had been 

 kept practically free for a month suddenh' became infested with 25 to 40 "beetles 

 each. 



Sprays and dusts were applied 6 times between June 10 and July 14 at intervals 

 of 4 to 10 days. Rain fell during each of these intervals and determined the 

 length of interval between applications. On June 26-29 rain fell on 4 successive 

 days and on July 11-13 on 3 successive days. During these rainy periods the 

 beetles migrated to the plants which were washed free of insecticides and heavy 

 reinfestations developed, especially on July 13 when 1937 beetles were counted 

 on 90 hills. 



Records of the effectiveness of insecticides were taken by counting the number 

 of beetles present just before spraying or dusting and again 24 hours after treat- 

 ment. On this basis cube-clay dust containing .75 percent rotenone reduced the 

 beetles 93.8 percent throughout the period and gave the best protection. Cube — 

 clay dust (.6 percent rotenone), copper oxychloride-lime dust 1-14 (DuPont), 

 copper-rotenone dust (.8 percent rotenone) (Gen. Chem.) and calcium arsenate- 

 lime dust 1-14 all gave 90 to 92 percent protection. Micronized rotenone-sulfur 



