GREEN FRUITWORM RESISTANCE TO GUTHION IN WESTERN MASSACHUSETTS! 



Glenn E. Morin and Roberta A. Spitko 

 New England Fruit Consultants 

 Lake Pleasant, Massachusetts 



In recent years, commercial apple growers in the Shelburne area of 

 western Massachusetts have experienced problems controlling (jreen fruitworm 

 larvae (GFW] with the standard insecticide Guthion* (azinphosmethyl ) . GFW 

 injury to fruit at harvest increased from a previously insignificant n.01% 

 in 1981 to greater than 4% in 1983 in one Shelburne orchard despite the tra- 

 ditional application of post-bloom Guthion* treatments. 



Were we witnessing the development of green fruitworm tolerance to 

 Guthion* or merely the cyclical appearance of a pest not well controlled by 

 this material? We have provided below a brief life history of GFW common to 

 Massachusetts, have described our attempts to identify this control problem 

 in one commercial orchard, and have included alternate strategies for 

 managing potentially resistant populations. 



Life History 



Green fruitworm adults appear in orchards and begin egglaying in late 

 March or earl/ April. Upon hatching, young larvae attack foliage and buds. 

 Larvae may va 'y from light to dark green with green head capsules and a pair 

 or pairs of lateral white stripes. Mature larvae chew holes in developing 

 fruits and may cause substantial injury. Larvae burrow into the soil in 

 late June and emerge as adults by the following April. Severely damaged 

 fruits abscise during the growing season. Minor damage generally appears on 

 fruit at harvest as large, superficial areas of light corky tissue but may be 

 so extensive as to expose the seed cavity. 



Field Observa t ions 



Increased GFW-like injury was first brought to our attention during the 

 1982 harvest season. Unfortunately, GFW damage is virtually indistinguish- 

 able from that of the oblique-banded leafroller without observations of lar- 

 vae at the time of initial injury. Careful monitoring the following season 

 was necessary to positively identify the culprit. 



In 1983, we initiated a foliar monitoring program at pink when chewing 

 injury to terninal growth was first noted. Terminal damage increased to 

 more than 30% by late bloom and limited injury to fruit clusters had begun. 

 Insecticide treatments were warranted to prevent excessive fruit injury and 

 full rate Guthion* applications were made at petal fall, first cover, and 

 second cover at 7-day intervals. These treatments were apparently unsatis- 

 factory as fruit cluster damage continued to increase and live GFW larvae 

 (tentatively identified as Orthosia hibisci "Guenee") were detected after 

 each application. Injury to fruit at harvest was greater than 4%. 



^We would like to express our appreciation to the Peck families of Valley 

 View Orchards in Shelburne, Massachusetts for their extreme level of 

 interest and cooperation in this investigation. 



*Trade name 



