60 MASS. EXPERIMENT STATION BULLETIN 339 



Plum Curculio in Apples. (W. D. Whitcomb, Waltham.) In 1936 about 

 25 percent of the hibernating plum curculio beetles had entered the trees by 

 May 15 when the calyx spray was applied. In comparison with past records, 

 this number is considerably greater than normal, and in seasons when it occurs 

 the value of a thorough petal-fall spray containing lead arsenate for combating 

 the plum curculio in apples is greatly increased. 



Normal curculio activity in 1936 extended from May 20 to June 10, and the 

 critical periods were marked by the warm weather of May 23 to 25 and June 

 lto4. 



In the experimental orchard only the Mcintosh trees had a uniform crop of 

 fruit, and the results are reported for that variety. 



Six experimental sprays for timeliness of application, using lead arsenate 

 and fish oil, were made at 3-day intervals from May 20 to June 4. The most 

 effective treatment was that applied on May 23 just before the maximum 

 activity of the first critical period. This date is two weeks earlier than the most 

 timely application in 1935. The least effective applications were those made 

 on May 26 and June 4 just after the increased activity on May 24 and June 2. 



The crop of Gravenstein, Baldwin, and Wealthy apples in the experimental 

 orchard was very small and scattered so that reliable deductions could not be 

 made, but it was evident that an application for controlling the plum curculio 

 which is timely on one of these varieties may not be timely and effective on 

 another variety. 



In the experimental spraying a soluble fish-oil spray, composed of 1 part of 

 soluble fish oil which increased the mixing and spreading, and 3 parts of regular 

 fish oil which maintained good adherence of the spray, was used with very 

 satisfactory results. 



Control of Red Spider. (W. D. Whitcomb, Waltham.) Further studies 

 of pyrethrum and derris extracts as used in commercial sprays showed that the 

 red spider mite is not satisfactorily controlled by pyrethrum extracts but that 

 extracts of derris, either as rotenone or as other extracted resins principally 

 deguelin, tephrosin, and toxicarol, gave satisfactory control in the proper con- 

 centrations. 



In these tests the emulsified extracts containing 10 percent sulfated alcohol 

 as a wetting and spreading agent were diluted 1-200 for application. A spray 

 containing 1 \^ percent pyrethrins had practically no effect on the red spider 

 and when the pyrethrins were increased to 2 percent, a relatively high concen- 

 tration, the mortality was only 9.52 percent. The addition of l / 2 percent rote- 

 none to the 1 Vo percent pyrethrins killed 37 percent of the red spiders, which is 

 poor control but indicates an increased toxicity of 35 percent due to the rote- 

 none. One percent pyrethrins and 1 percent rotenone combined averaged 

 79.65 percent mortality; and 2 percent rotenone without pyrethrins killed 

 87.16 percent of the red spiders and was the most effective formula used in this 

 series. 



Spray mixtures containing "other extracted resins" of derris were approxi- 

 mately one half as toxic to red spider as rotenone, and when used at twice 

 the concentration produced an equal or slightly greater mortality of this pest. 



A summarv of the results is as follows: 



