ANNUAL REPORT, 1939 57 



Control of Cabbage Maggot. (W. D. Whitcomb, Waltham.) Eggs of the 

 cabbage maggot were first found at Waltham on May 10, which is within the 

 average period for the past eight years. Infestation was slightly greater than 

 normal as indicated by 87 percent commercial damage to untreated cabbage. 

 In spite of favorable growing conditions during May and June, only about one- 

 fourth of the untreated plants developed marketable heads. 



Corrosive sublimate solution (1 ounce dissolved m 10 gallons of water) was 

 again the most eflfective treatment. One application on May 13 gave 98.67 

 percent commercial protection and produced 87.25 percent marketable heads, 

 while two applications on May 13 and 20 gave 99.33 percent commercial pro- 

 tection with 93.25 percent marketable heads. Root treatments with calomel-talc 

 dusts containing 25 percent calomel or more gave at least 90 percent protection, 

 but dusts containing 10 percent calomel permitted 17.57 percent commercial 

 injury, and a 5 percent calomel dust allowed 38.93 percent moderate or severe 

 infestation. However, plants receiving root treatment with 50 percent calomel 

 or more produced only 57 to 70 percent marketable heads, indicating a delayed 

 growth as well as protection from maggots. In comparison, the plants receiving 

 5 to 25 percent calomel dust on the roots produced 78 to 80 percent marketable 

 heads in spite of relatively severe damage by maggots. A 50 percent calomel 

 dust with a gypsum carrier gave definitely better maggot protection with a greater 

 yield of marketable cabbage, in spite of apparently poor adhesion when applied, 

 than did a 50 percent calomel-talc dust. 



A comparison of the susceptibility of cruciferous vegetables to maggot injury 

 shows the commercial injury as follows: Cauliflower 100 percent; collards 88 

 percent; cabbage 87 percent; kohl-rabi and broccoli 84 percent; Chinese cabbage 

 64 percent; and Brussels sprouts 56 percent. 



On radishes two dustings with 5 percent calomel-talc dust or sprayings with 

 calomel-gum arable suspension (1 ounce in 23^ gallons of water) applied 7 and 

 14 days after the seed was sown increased the average protection against maggots 

 11 percent in eight plantings from May 1 to July 10. In spite of this protection, 

 20 percent of the radishes were unmarketable and the treatment does not appear 

 practical. Radishes grown from seed planted without treatment on May 29 

 and after July 10 had little or no damage from the maggot, while 30 to 60 percent 

 of those planted May 1 to 20 and June 10 to 30 were infested. 



Control of Squash Vine Borer. (W. D. Whitcomb, Waltham.) The field 

 infestation by the squash vine borer in unsprayed Hubbard squash in the experi- 

 mental planting at Waltham in 1939 was 3.24 borers per vine. This is about the 

 average infestation during the last five years. However, favorable growing 

 conditions produced the best yield of squash ever recorded and this yield was not 

 greatly influenced by the borer infestation. 



Insecticides were applied on July 6, 13, 20, and 27. Liquid sprays were much 

 more effective than dusts. Nicotine sulfate 1-250 and nicotine sulfate 1-500 

 plus summer oil emulsion 1 percent reduced the number of borers per vine 74 

 and 77 percent respectively, while wettable derris spray (4 pounds in 100 gallons) 

 with a resin sticker caused a 35 percent reduction. Derris-clay dust (.75 percent 

 rotenone) failed to reduce the borer infestation, while a commercial copper-rotenone 

 dust (.8 percent rotenone) and a commercial dust containing calcium arsenate, 

 red copper oxide, flour, and talc permitted an increase of 27 and 33 percent in the 

 number of borers per vine. 



In spite of the borer infestation, the vines which received dust treatments 

 yielded 10 pounds more marketable squash per vine than those receiving liquid 

 sprays. The best yield (50.64 pounds per vine) was obtained from the vines 

 receiving copper-rotenone dust, while vines receiving nicotine sulfate 1-250 as 

 a spray yielded 35.08 pounds per vine. Increased yields in the dusted rows were 



