Green tip apple scab management

April 24, 2014

Orchards in most areas of the state should be showing green tip now, and that means that protection is required to manage apple scab. Many orchards are going into this season with high overwintering inoculum as a result of the wet 2013 growing season, and growers need to be vigilant to manage this season’s disease. Wind conditions look good tomorrow, Friday April 25, for spray applications. However, there is a good chance of frost first thing in the morning. This means that oil should not be applied in sprays for the next couple of days until you have a good window of frost-free weather for 48 hours before and after application. It’s also good to make sure that sprayers are parked in a warm area overnight or all water drained from pumps, hoses, control valves, and booms. I have had booms split when filled with water and held at 28 °F. Remember, stainless steel booms are great for corrosion resistance, but stainless is a relatively brittle metal that easily splits from freeze damage.

Based on scab models run in the NEWA system ( apple scab ascospore maturity ranges from 2% to about 5% in the Champlain and Connecticut River Valleys. Some orchards saw a likely scab infection yesterday if green tissue was showing and mature inoculum present. Inland and upland orchards may just barely be showing green tissue, but upcoming wet weather and moderate temperatures will likely lead to an infection over the weekend.

Orchards are best protected now with copper, EBDC, or Captan fungicides. Do not apply Captan if you have or will be applying oil within 10-14 days before or after application. If orchards were uncovered prior to a likely infection in the past couple of days, Vangard or Scala applied tomorrow will provide some kick-back activity. Any postinfection materials should be combined with a full label rate of a protectant material to minimize the risk of the apple scab fungus developing resistance. Specific rates and use recommendations can be found in the 2014 New England Tree Fruit Management Guide. Please contact me if your guide is out-of-date and you need a new one.

You have calibrated you sprayer, right?

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.