34 MASS. EXPERIMENT STATION BULLETIN 417 



In summer applications of DN-IU at Waltham, on Mcintosh and Northern 

 Spy trees infested with 18 to 21 European red mites per leaf on July 28, a spray of 

 DN-111, 1 pound in 100 gallons, and a spray of DN-111, 1 pound, lead arsenate 

 3 pounds, and wettable sulfur 4 pounds in 100 gallons, each reduced the popula- 

 tion of mites 98 percent six days after the treatment. A natural reduction of 11 

 percent occurred on the unsprayed trees during this period. Thirteen days after 

 these sprays were applied, the mite population had been reduced 97 percent. 

 The natural reduction on unsprayed trees was 94 percent. 



On Baldwin trees having an infestation of 381 white apple leafhoppers per 100 

 leaves on August 31, a spray of DN-111, 1 pound in 100 gallons, reduced the 

 population 94.7 percent eight days later, while a natural decrease of 9.02 percent 

 occurred on unsprayed trees. 



Potato Spraying Experiments. (A. I. Bourne.) The experimental plots were 

 planted May 7, and the plants in all the plots were alive and green up to the first 

 killing frost on October 5 and 6. The potatoes were dug (by machine), picked, 

 , and bagged on October 13. 



Potato flea beetles appeared as soon as the plants were above ground and per 

 sisted in great abundance until mid-August. 



Leafhopper infestation was comparatively light, and no records of serious out- 

 breaks were received. 



During late June and early July there was a very considerable amount of stalk 

 infestation by European corn borer larvae. While the number of injured stems 

 was high, most of the damage was confined to lateral stems, so that for the most 

 part the attack simply caused a moderate pruning and the injured growth was 

 very soon replaced. Hundreds of second-brood moths were harbored among the 

 plants during the day, but there was little or no evidence of late-summer injury 

 by second-brood larvae. 



Potato aphids developed a serious infestation following the very hot and dry 

 weather of early July. Delay in applying control measures and temporary local 

 shortages of nicotine allowed serious infestations to build up in several large 

 commercial plantings. A thorough application of nicotine in the sprays of July 

 20 and 28 eliminated these insects as a source of danger in the experimental plots. 

 These two applications were made on bright, sunshiny days with temperature 

 ranging from 84° to 86° to facilitate the rapid evolution of nicotine. 



The test plots received 10 applications at approximately weekly intervals from 

 July 15 to September 3. Because of the war emergency and to conserve copper, 

 the bordeaux mixture was based on a 8-8-100 formula instead of the standard 

 10-10-100 strength. 



There was practically no disease in any of the plots. Out of more than 233 

 bushels of potatoes harvested, only 18 pounds were discarded because of disease. 

 Evaluation of the different treatments on the basis of flea beetle damage showed 

 a definite increase in protection following the use of calcium arsenate. The addi- 

 tion of calcium arsenate reduced flea beetle damage by 163^ percent in the plots 

 which received the standard 4-4-50 bordeaux; in the plots which received the 

 4-2-50 bordeaux the reduction was 323^ percent; and in the plots which received 

 half strengh bordeaux the reduction was 35 1/3 percent. In all the plots in 

 which bordeaux plus calcium arsenate was applied, the average number of leaf 

 punctures per square inch of leaf surface was practically the same regardless of 

 the strengh of bordeaux. There was a marked difference, however, in the amount 

 of flea beetle feeding in the plots which received bordeaux alone. Compared with 

 t^he 4-4-50 plot, the avqrage number of feeding punctures per square inch of leaf 

 surface in the low calcium plot was 28 percent greater; and in the 2-2-50 bor- 



