Arthropod Management Update

Degree Day Accumulation and Arthropod "Events"

The following table has the updated estimated degree day accumulation for  six sites around Vermont  as of  May 20.  Also, the "Guide to Arthropod Pest Events" is printed again. 

Plum Curculio -- Degree Day Model to Predict Protection Period

Please note that the risk of plum curculio damage increases after there have been 3-4 days of average temperature of 55-60F, or 2 days of maximum temperatures above 75F after petal fall. 

As the 2000-2001 New England Apple Pest Management Guide states,  research in New York has found that degree day (DD) accumulation is a useful predictor of how long protection is needed against plum curculio (PC).   The model is based on the assumption that insecticide residues for the control of PC after Petal Fall  (PF) are maintained until 40% of the egg-laying activity is completed, which is predicted to occur at 340 DD (Base 50F) after PF.   A strategy of how to use this information is:  apply an insecticide effective against PC to the entire orchard at PF;  start calculating DD at 95% PF;  maintain insecticide residue by additional applications until 340 DD have accumulated;  no additional sprays are necessary if the date on which 340 DD was reached is less than 10-14 days from the last spray. 


Leafminers -- Sap-feeding Mine Stage

Leafminer sap-feeding mines should be visible on the undersurface of cluster leaves.  It is important to determine if  the threshold has been met before 10% of the mines reach the tissue-feeding stage.  Options include Agri-mek, Provado, and Spintor.  Please see the NEAPMG for details on these materials that will impact their effectiveness.   Also  see  the  "In the Spotlight"  section of this newsletter for threshold levels and pictures. 



European Red Mite Thresholds

White Apple Leafhopper

White apple leafhoppers (WAL) overwinter as eggs under the bark of twigs. Eggs begin to hatch during bloom, and usually by petal fall, the nymphs can be seen moving around on  the underside of a leaves.     The threshold for  first generation of WAL is 25 nymph and adults/100 leaves.   





Codling Moth Flight Expected

We caught three moths in our CM pheromone traps on May 15th but their true identity is in question.   We have not had a sustained capture of this insect yet at the UVM Hort. Res. Center.    In orchards were CM are a problem, a DD model can aid in management by helping to time insecticides.  (e.g., applying an insecticide between 250-360 DD from first adult pheromone trap capture for 1st generation CM).