Apple maggot, the calm before harvest

By Terence Bradshaw

Pardon my absence these past few week- a trip to beautiful Istanbul, where I presented some of our research from the past couple of years on cider apple management, and both wrapping up and starting a new course have kept me a bit distracted. Nonetheless, we have continued to scout in Vermont orchards, and overall, things are looking good. Rains came when needed (although more growers need irrigation for summers like this), thinning was decent so fruit size is good, scab is minimal. For growers who haven’t yet applied a stop-drop material, there is still time to get some Retain on. See my August 2016 post for more instruction on its use to help reduce drop and delay maturity to help manage the harvest.

Of greater concern is the seeming invasion of apple maggot fly (AM) this summer. In every orchard we’re scouting, these insects have been caught at above-threshold numbers, and, in a few2 places some pretty alarming numbers. I’ve seen a little damage on some early varieties but by and large not a massive outbreak of damaged fruit- yet. I’ll be looking into this more as the season commences and may tap some orchards for spray records to get a handle on this. AM used to be fairly easy to kill with organophosphate insecticides, which also persisted on the fruit for a good while and thus were very effective against this pest which may have a long emergence period over the majority of the summer in some situations. As we’ve shifted away from OPs for pest management in Vermont orchards (and that’s not a bad thing), I think that this pest is slipping through the cracks a bit. Growers are relying on Assail as the default material, and I am starting to question how effective that material really is, or if there is possibly an issue with resistance development in the AM population to that material.

For orchards with sustained, very high populations (10+ flies per baited trap), a final application against AM may be called for, especially if your last spray was some time ago or you have late cultivars. Materials are listed in the New England Tree Fruit Management Guide, and in addition to that table, Delegate and Entrust (the latter is organic certified)may be reasonable choices, especially if you want to rotate chemistries but still avoid using OPs. However, watch your preharvest intervals.

Generally, late-season (September-October) AM flights aren’t thought to lead to significant egglaying and subsequent fruit damage, so don’t sweat it too much as we get into harvest. I’ll work with the best experts in the region over the winter to see how we can better develop a management program for this pest.

Good luck with harvest, Terry

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