VT Apple IPM: cool temps and rain (snow?) ahead

April 14, 2021: The forecast for the end of this week keeps looking worse- or better, depending on your point of view. Many of us are concerned about the advanced bud development on trees, which is about two weeks ahead of normal in some sites. We had McIntosh at tight cluster over the weekend on 4/11, and there’s still a lot of chilly weather ahead, so frost risk is certainly a concern. Next week’s cool down should be very welcome to slow down bud development, yet doesn’t look cold enough to do any damage. For now, we look like we’re in the clear. I don’t recommend miracle frost fixes from a jug, but this is a good time to get ready to apply foliar nutrients to boost bud viability. I’ll discuss some options for frost management later, should that risk get more real.

Oil should have been applied in most orchards in warmer sites by now, as well as a full rate of copper. Chances of precipitation starting tomorrow Thursday April 15 look greater than initially thought, and central and southern Vermont orchards can expect some much needed rain. That brings to mind a potential apple scab infection period. However, ascospore maturity is relatively low, and expected spore release from this next event is estimated at 3-6 percent of the total inoculum load for the year. Given the dry weather last year, scab was really hard to find and overwintering inoculum should be quite low. Recent copper applications will cover for this infection, but applications more than a week ago or sites with more advanced tissue and greater likelihood of rain (Southern VT) ought to consider either a protectant fungicide application now or a postinfection material like Scala, Vangard, or Syllit to be put on after things quiet down, say Saturday morning. Cooler inland sites likely don’t have enough spore development of tissue exposed to worry about this one- get your copper on when you can, but no rush.

Insect pressure is low- we haven’t seen anything at UVM orchard, and for most growers, early season insects aren’t really an issue. Wholesale apple producers with very low tolerance for cosmetic damage should keep an eye out for tarnished plant bug (described in my last message).

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