Thinning and codling moth management in Vermont orchards

June 4, 2014

By now apple fruitlets in the Champlain and Connecticut Valleys should be approaching 10-12 mm size which is the most receptive time for thinner application. Bloom and fruit set have been spotty this season, with large variations across cultivars and even within cultivars on adjacent trees in a row. Still, don’t plan on skimping on thinning. We often see more fruit than we thought we had as they size up. On trees with sparse bloom, given good pollination conditions, more of those fruit will tend to set as well, so those clusters will need thinning. I recommend thinning the whole orchard at a moderate dose (say 1 qt carbaryl plus 2.5 – 5 ppm NAA), then following up more heavily-set trees with hand thinning. Cool days ahead suggest a slight increase in thinner rates may be appropriate to get best results.

Codling moth adults are now flying, and egg hatch has just barely begun. Based on Glen Koehler’s Orchard Radar model, the best timing to apply materials targeted at hatching larvae is next week, followed by a second spray 7-10 days afterward. In orchards with historically low CM populations where a single spray has been effective in managing the first generation this pest, the model suggests application the week of June 16.

Keep covered for plum curculio in the meantime, orchards that had a full-block insecticide applied at or soon after petal fall (that’s all of you, right?) can apply sprays only to the outer two or three rows to maintain efficacy against migrating beetles.

Terence Bradshaw, UVM Tree Fruit and Viticulture Specialist

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The UVM Tree Fruit and Viticulture Program is supported by the University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM Grant, and USDA Risk Management Agency Funds.

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