THE PLUM CURCULIO IN APPLES 



45 



Gravenstein develops rapidly, and should be sprayed before such late develop- 

 ing varieties as Northern Spy and Mcintosh. 



Materials. 



Stomach Poisons. Lead arsenate in the powdered form is the standard 

 insecticide in use for the control of the plum curculio as well as other leaf 

 or fruit-eating orchard insects. Laboratory experiments with this poison 

 have shown that beetles feeding on sprayed apples die in two to ten days, 

 and orchard spraying experiments have indicated commercial control from 

 its use in a well-timed spray schedule. Two pounds of powdered lead arse- 

 nate in each 50 gallons of water is the most practical dosage in curculio sprays 

 for Massachusetts apple orchards. 



Calcium arsenate contains a higher percentage of the active agent, arsenic 

 oxide, than lead arsenate and has been slightly more effective under labora- 

 tory conditions when used in equal parts by weight. On orchard 'trees 

 calcium arsenate is generally used with equal or more parts of lime to pre- 

 vent foliage injury and fruit russeting, but the Hme tends to reduce its 

 effectiveness. No orchard experiments with calcium arsenate have been 

 conducted on this project but recent work in New Hampshire (2) has shown 

 that V/i pounds of calcium arsenate in lime-sulfur solution diluted to 1 gal- 

 lon in each 50 gallons of water, without additional lime, can be used with 

 more safety than lead arsenate in the same formula. Until further work 

 has been done, however, lead arsenate is preferred to calcium arsenate for 

 plum curculio control in Massachusetts. 



The results of some of the laboratory experiments in comparing these 

 materials are shown in Table 13. 



Table 13.— Effect of Lead Arsenate and Calcium Arsenate Sprays on the 

 Control of Plum CurcuUo Beetles on Apples. June 11 — 28, 1928. 



Estimated — Apples dried or covered with punctures, making accurate count 

 impossible. 



