Apple crop management this week

By Terence Bradshaw

Apple buds are rapidly expanding into tight cluster bud stage in most of Vermont, which sets the calendar close to ‘normal’ after the cool, slow start to the season. Apple scab infection periods have been somewhat scarce, depending on when you started you clock for ascospore maturity (green tip, minus any confidence you have in slow maturation of a low inoculum population because your orchard was clean last year). We potentially had an infection period April 27-May 1 right at green tip with low ascospore maturity and little tissue open; some had an infection period May 3-4, and others may be waiting for the first one that could occur today and into tomorrow. You should be covered with a protectant going into this event, and if you aren’t or question your coverage, plan on applying a material with kick-back activity like one of the Lunas, Merivon, Inspire Super, or even one of the older strobilurins or DMI fungicides (if they still work against your local population) this morning or early tomorrow.

Once we get through today’s rains (and the likely overnight wetting event), the warm, sunny weather this week is going to push disease management to the side for a spell but will push bud phenology and insect activity along. Growers who use them should already have traps deployed for tarnished plant bug (TPB) and European apple sawfly (EAS), which are attracted to blossoms (thus the use of white sticky cards to catch them in the canopy). Compare cumulative mean catch per block to our monitoring chart to determine the need to treat.

That said, there are important considerations to make when determining the need for prebloom insecticides. At the time the accepted thresholds were established, the majority of Vermont’s apples were sold to wholesale markets with little tolerance for cosmetic blemishes like TPB or a low infestation of EAS may cause. However, increased direct-marketing of apples today may increase consumer tolerance for those ‘ugly’ fruit, so really consider your own tolerance for damage before applying a broad-spectrum material. Then again, I’ve seen EAS infestations that looked worse than an unmanaged codling moth outbreak and where the larvae feed into the core, causing fruit abscission instead of just cosmetic injury. If you’ve had a history of EAS and show a high population on traps, that one may be worth treating. However, if bloom is short, a petal fall application may be preferable.

I am making all of these caveats because of the concern for impacts of spraying on wild and managed pollinators. Dr. Rufus Isaacs at Michigan state University recently posted a good summary of consideration in reducing risk of pesticide impact on pollinators, which I summarize here but you can follow the link to read in full:

· Use integrated pest management (IPM) to reduce the need for sprays.

· Avoid pesticide sprays during crop bloom.

· Apply pesticides after sunset or before sunrise, or when air temperature is below 50°F.

· Select the least toxic pesticides and formulations when possible.

· Reduce drift onto areas outside crop fields.

· Remove flowering weeds from crops.

· Provide bee-friendly habitat away from crops.

· Develop and implement a pollination contract with your beekeeper.

That last one should remind everyone that it’s time to get our bees lined up if you’re planning to rent hives. My old mentor Lorraine Berkett used to have us make bets on when the first McIntosh blossom would open in South Burlington. This year, I’m guessing May 11.

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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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