PLUM CURCULIO IN APPLES 15 



RECOMMENDATIONS 



In many states the recommendations for combating the plum curcuho on 

 apples with insecticides are to spray or dust from 7 to 10 days after the petal-fall 

 stage, and in many seasons applications at this time are timely. However, the 

 experiments reported herein, together with observations during the past six 

 years, indicate that the stimulation in activity by high maximum temperature 

 is an important factor in determining the most timely application of insecticides. 



Therefore the recommendations for combating the plum curculio on apples 

 in Massachusetts are: 



After the blossom petals have fallen, apply a special spray or dust in 

 the first period of warm weather when the maximum temperature 

 reaches 75° F. or higher and such temperatures promise to continue for 

 2 or more successive days. Use 4 or 5 pounds of lead arsenate in 100 gal- 

 lons of spray, preferably with the addition of 1 pint of fish oil or linseed 

 oil as a spreader and sticker. Except in severe infestations, 85-15 sulfur- 

 lead arsenate dust can be substituted for the spray. When there are 

 two distinct periods of high temperature within 15 days after the proper 

 time for the calyx spray, apply a spray or dust in each period, using the 

 same materials, and determining the time of application by the same 

 temperature requirements as before. On scab susceptible varieties, or 

 where the addition of a fungicide is desirable for any reason, liquid lime- 

 sulfur or a similar material can be added to the spray without danger 

 of greatly decreasing the efficiency of the mixture for combating the 

 plum curculio. 



SUMMARY 



Studies of the plum curculio at controlled temperatures of 55°, 65°, 75° 

 and 85 °F. indicated that 75° F. is very near the optimum temperature for the 

 development of the immature stages and the activity of the adults of this insect. 



At 55° F. development of the immature stages was not completed, and at 

 85 ° F. development was practically the same as at 75 ° F. 



Adults feed little and lay few eggs at 55° F., but make an average of 6.675 

 punctures per beetle per clay when confined at 75 ° F. during the height of their 

 activity. 



The number of days which plum curculio beetles lived when feeding on poi- 

 soned fruit decreased with each increase of 10 degrees in temperature from 55° 

 to 85° F., and each increase in the concentration of lead arsenate from 3 to 4 

 to 5 pounds in 100 gallons of water. 



Lead arsenate at the rate of 6 pounds in 100 gallons of water is apparently 

 repellent to the plum curculio. 



Five pounds in 100 gallons of water appears to be the most effective concen- 

 tration of lead arsenate although its advantage over 4 pounds in 100 gallons is 

 small. 



The addition of fish oil to lead arsenate results in a slight increase in effective- 

 ness, and its use is recommended especially to aid the sticking and spreading 

 of the spray to the fruit and foliage. 



The addition of lime-sulfur and chemical hydrated lime to lead arsenate-fish 

 oil does not decrease the effectiveness of the combination at high temperatures. 



The variable temperature in Massachusetts has a noticeable influence on the 

 activity of the plum curculio, and spray applications should be timed according 

 to the temperature. (See Reconunendations.) 



