West Michigan tree fruit update - June 26, 2018

Several insects need to be managed carefully.

Horticultural concerns

Apple are sizing nicely with overall variety. Fruit size is right on target or slightly larger than models predict. Hand thinning is being done in some blocks (Gala in particular). The potential for sunburn in apples is of real concern with the very hot temperatures predicted for the coming weekend. This could affect high value varieties, highly prone to sunburn (especially Honeycrisp). Protectant materials should be considered, keeping in mind that once you start applying them, you should continue to apply season long.

The Grand Rapids area has not had the rain the south and north have seen, so the need for irrigation is of concern. Most growers started running irrigation systems in the last week or two, and should continue to do so, unless we get at least an inch of rainfall in the next week or so.

Sweet cherry harvest will begin this week and there is a great deal of variability in fruit set being reported. No varieties are set heavy and a few blocks have nearly no crop. Recent rains have caused fruit cracking in some prone varieties.

Tree fruit insects

Adult trap numbers of codling moth continue in normal numbers. We should be just past peak egg hatch and cover sprays are critical. A regional biofix was set for May 25, 2018 (313 DD50) with 591 degree days base 50 accumulated since that date using Sparta Weather data. Adult flight should begin to decline as we are past peak flight. Larval activity is expected to continue through the second week of July and cover sprays are critical until then.

Traps continue to be very low or at zeros for spotted wing Drosophila. With cherries in straw color or red stages, cover sprays should be considered as fruit might ripen quickly. Watch PHI’s for various pesticides used. Continue to trap for flies in ripening crops – cherries especially.

Adult flight of obliquebanded leafroller continues. We're probably just at (or slightly past) peak adult flight. A regional biofix was set for June 11, 2018 (1042 DD42) with 405 DD42 accumulating since then, for the Sparta Enviroweather station. We should be at first larval hatch and cover sprays in high pressure blocks should be considered. Low pressure blocks can scout for larvae and spray if needed – perhaps just after the 4th of July. The upcoming nice, warm temperatures will be good for Bt activity should you choose to use that product.

San Jose Scale crawlers were first found in the Grand Rapids area last week. A regional biofix was set for May 25, 2018 (286 DD51) with 560 degree days base 51 accumulated since that date for Sparta. Contact insecticides should be applied now to target crawlers before they reach the white cap stage.

Reports of apple maggot from southern areas of Michigan should make the Grand Rapids area take notice and get maggot traps in place ASAP. I suspect they are more active with higher levels of rainfall in southern Michigan, but it’s worth watching.

Mites are present in apples and other tree fruits. All stages of European red mite and twospotted spider mites are now present. Some off color of trees is noticeable. No bronzing yet, but you can tell blocks with high numbers. The threshold for all mites is 2.5 mites per leaf for June. The presence of predators also should be taken in to account.


Very few aphids are present overall in Grand Rapids area orchards. Woolly apple aphids are now being found in tree canopies and at this early stage management is highly effective in blocks that had high pressure at the end of 2017. Continue to scout for all aphid species and be on the lookout for predators.

Brown marmorated stink bug adults seem to be higher in number this spring than ever before. This might be the year to not ignore BMSB any longer. Continue to monitor.

Second generation oriental fruit moth adult flight is starting in the Grand Rapids area and right on target with degree day models. A regional biofix was set for May 10, 2018 (272 DD45) with 960 degree days base 45 accumulated since that date. Early egg hatch should be starting with the 10 percent egg hatch stage reached next week. Cover sprays will become important again the first week of July in stone fruits and potentially in nursery apple trees.

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