36 MASS. EXPERIMENT STATION BULLETIN 441 



the field rather wet and checked growth somewhat. Most of the plants remained 

 alive and green until killed by frost October 13-14 (the first serious killing frost). 

 The field was dug October 14. Damage from excessive water was such that 

 records could be taken only from the higher portion of the field. 



Flea beetles were slightly less than normal in abundance; the early attack was 

 very light. A rapid and heavy build-up of leafhoppers occurred between July 

 17 and 25, One application of DDT (1 pound actual) in 10-5-100 Bordeaux on 

 the 25th not only practically eliminated leafhoppers but wiped out the late brood 

 of flea beetles; neither insect was present in any amount for the remainder of the 

 season. Potato aphids began to appear in all plots about mid-July during the 

 hot dry weather which prevailed at that time. The infestation uas subdued with 

 nicotine sulfate in the application of July 17, The records indicate that the 

 application of DDT practically eliminated insect pests with the exception of 

 potato aphids, and even in the case of potato aphids prevented a serious build-up. 

 By mid-August practically all insects had been eliminated and the insignificant 

 damage to foliage was shown by records of flea beetle perforations on the foliage: 

 6.4 punctures per growing tip on August 17 and 2.5 punctures per growing tip 

 on August 20. 



•Sprays were applied at approximately 7-day intervals from June 12 when the 

 plants were about 4 to 6 inches high until September 18 when most of the plants 

 were still green but were beginning to ripen. The sprays from August 28 were for 

 protection of green tips only. There was practically no evidence of insect pres- 

 ence after early August. 



Evidence from these tests, as well as results of experiments elsewhere, indicate 

 tnat DDT is very effective against the major insect pests of potato. In laboratory 

 and field tests, DDT either as a dust or as a spray controlled Colorado potato 

 beetle, leafhoppers, flea beetles, and plant bugs, if thoroughly applied to reach 

 both upper and under leaf surfaces. There is indication that potato aphids can 

 be held to low numbers by a regular schedule of DDT, although there is still 

 some doubt whether heavy outbreaks will be checked quickly enough to prevent 

 damage when DDT dusts or wettable powders are used. 



Control of Onion Thiips. (A. I. Bourne.) The test plots were planted to 

 onion sets April 18. Cool dry weather slowed early development somewhat, but 

 with plentiful rainfall in May and early June, growth was more normal and the 

 plants made rapid advance. The growth was checked somewhat by the 5-week 

 period of dry weather which followed. The plants had become well established 

 by mid-June so that the check. was not serious, and the plots matured a good crop 

 which was ready to harvest by early August. 



Thrips were delaj'ed somewhat In early spring by the cold weather but found 

 the hot dry weather of late June and July very favorable, and built up rapidly. 

 Throughout the Connecticut Valley, thrips were not of serious abundance; set 

 onions escaped any appreciable injury, and the small plantings of seed onions 

 were not seriously attacked. 



Black Leaf 40 and derris sprays again gave consistently high control in all 

 cases. Ryanex, DDT, and DDD sprays also proved effective (above 90 percent 

 effective control). DDT and DDD were superior to the other sprays in residual 

 effects, allowing no increase In thrips population during a 7-day period following 

 application. 



Of the dusts, Multicide and Multlcide + pyrethrum gave a consistently high 

 degree of immediate protection and good residual effects. Following a very heavy 



