Orchard pest management, late July

By Terence Bradshaw

Many growers, especially of pick-your-own or retail-sold fruit, are starting to think about wrapping up the pest management season for 2017. Before doing so, it is important to consider late-season insect and disease pests that could affect the crop going into harvest.

Apple maggot numbers ticked up in a lot of orchards last week so most sites that have a problem with that pest have reached the threshold for treatment. AM is relatively easy to manage and there are many materials labeled for doing so- Assail is probably the most commonly-used one, as well as Delegate or Altacor (good if you also have problems with lepidopteran pests), or Avaunt. Pyrethroids are also quite effective against this pest, but they are harsh on beneficial predatory mite species and thus their use after pink bud stage can cause flareups of mites and other secondary pests. Imidan is another old-guard material in the organophosphate class, but its use has been substantially restricted, and as a whole, we are encouraging growers to move past it. Organic growers can use a trapout strategy which would need to have been in place already to be effective; in lieu of that, carefully-timed application of spinosad (Entrust) or pyganic may be effective, although the latter breaks down very quickly in sunlight and thus cannot be counted on for any residual control.

We remain between generations for codling moth in most orchards. It would be best to keep an eye on NEWA for timing the management of the second generation. Application of a material effective against hatching eggs and young instar larvae is best applied at 250 degree days after moths begin flight, which is right about now. That would put us at about the first week of August to treat in warmer production areas of Vermont.

Mites are mostly a non-concern around the state except in certain problem areas, especially where pyrethroid insecticides are used to manage other pests. Scouting is the best way to determine need for treatment at this stage, and should be performed regularly and using the Cornell sequential mite sampling guidelines (here, page 15) as a reference.

Summer diseases-sooty blotch/flyspeck, late-season apple scab (if you didn’t control it in the spring), and rots (particularly black rot in Honeycrisp) are of particular concern, given the wet weather that has continued this season. Maintaining fungicides on a 14-20 day schedule should be the minimum.

Calcium will be important to maintain fruit quality and to reduce bitter pit; it should be in every tank that you’re spraying, especially for large-fruit cultivars.

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