Apple scab infection period

By Terence Bradshaw

Okay, today was wet. Without question this was a substantial apple scab infection period. Fire blight- I’m still on the fence an lean towards ‘not a problem’ unless you had a substantial amount last year and have susceptible cultivars. NEWA estimates across the state suggest that 12-30% of the entire season’s apple ascospores were discharged today. What does that mean?

If you went in to this rain event with a full, as in 6 lb/acre of mancozeb or 5 lb/acre captan applied in the past five days, you’re probably good. Any less than that, and you should really consider coming in in the next 48 hours with a material with post-infection activity, like one of the DMIs, QOIs, or SDHIs. If those look like alphabet soup to you, check your New England Tree Fruit Management Guide for some more clarity. Organic growers should get more sulfur on, and if coverage was questionable, this is a time when lime sulfur may be called for to burn out germinating spores before infection gets too ahead of things.

For those with stone fruit, this was also likely a major brown rot infection period, so trees should be covered with a suitable material in the DMI or QOI classes within this same time window.

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