VT Apple IPM: (early?) petal fall on apples

Apple scab is still a concern in Vermont orchards. However, as heat gas continued to accumulate and relatively regular showers have provided for spore release from leaf litter, the supply of inoculum available to infect orchards, assuming you have prevented infection during these wetting events, is dwindling. The NEWA model in some sites shows up to 99% spore discharge by the end of this week, but like all models, we need to be careful as reality on the ground may be off by as much as 10%, which can be enough top cause infection. Bottom line- don’t let your guard down on scab yet, but this does look like an early-ending scab season. Stay covered and we’ll revisit next week.

Normally when we think of a cool / downright cold spell after a warm stretch conducive to fire blight, we consider the risk to decline with the temperatures. However, all of the usual fire blight models predict continued risk to blooming trees today and into this week. As there are fewer blossoms out there in many orchards (although inland/upland orchards may be in full bloom still), it may be easy to think that we’re out of the woods. However, I would consider treating high value blocks of young trees of fire blight-susceptible varieties, at a minimum (cider varieties, Gala, Mutsu, Cortland, Paulared, Northern Spy, Fuji, Macoun, etc). Word on the street has it that the streptomycin supply is low to unavailable. I’d suggest treating what you can with what you have, consider Apogee / Kudos even at half-rate to reduce shoot blight, and paying close attention to strikes as they show (and cutting them out aggressively).

Many folks are seeing the beginnings of petal fall and are considering an insecticide or thinning treatment containing carbaryl. Please reconsider that if you have any bloom, including in groundcover, in the orchard. I can’t in good conscience (nor legally, in keeping with the insecticide labels) recommend both treating blossoms with streptomycin while also applying an insecticide in a thinning program. So if you have blossoms but want to thin, I’d recommend NAA (Refine) or 6-BA (Maxcel) alone without carbaryl. This looks like a decent week for thinning.

Spray conditions look best tonight (Monday May 23) though Wednesday.