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IPM Message for Cranberry Growers: Apr 27, 2015

April 27, 2015

Frost season is underway! As of April 23rd, most bogs had reached white bud stage. Some bogs that iced-out late were lagging behind a bit. Starting on April 27th and updated as the plants advance, photos of tolerance stages will be posted on the Station website.

Winter moth found on cranberry! The Entomology Lab reports tiny winter moth (WM) larvae have been picked up in sweeps in Plymouth and Rochester! Despite temps below 60, a few larvae per sweep net have been found. They are incredibly tiny but they are out.

If you are going to treat for WM, consider Intrepid, Avaunt or Delegate given that larvae can now be found; they will only grow bigger by eating the tiny buds! Although the numbers may be below threshold, they will get into buds and may be harder to kill once inside. The threshold of 18 per sweep set is not a long-standing "tested" number; it is a guideline to help management. Consider only treating pieces where the higher numbers are found and perhaps at reduced rates of insecticide, and then sweep again. Possibly, the larvae are from the bog and a spray would stop them, but it is also possible larvae may come in from surrounding blueberries and trees and may continue "ballooning" in, and maybe both. Another consideration is size of cranberry bud… if the buds are too small, larvae may just die, if buds are bigger (i.e., sanded pieces, early varieties, warm locations) larvae may do well and grow faster.

Heather Faubert, University of Rhode Island Extension reports that winter moth eggs started hatching on April 19. Over the past week, all the eggs at the monitoring tree in Kingston, RI have turned blue and hatched. She expects all eggs have hatched by now in our area as well.

cranberry leaf on left side and tiny larva on right winter moth larva and its frass in blueberry

Left photo: cranberry leaf on left side and tiny larva on right (photo courtesy Erika Saalau Rojas).
Right photo: shows winter moth larva and its frass in blueberry (photo courtesy Heather Faubert, URI).