West central Michigan tree fruit regional report – July 28, 2015

Sweet cherry harvest is over and peach harvest is underway.

This week brings very hot weather and, while we had some very heavy rains about 10 days ago, the need for irrigation should be considered where soils are lighter and for young trees. Watch the pre-harvest intervals (PHI) of spray materials you are using for all tree fruits as we approach harvest dates.

Tree fruit diseases

Apple scab and powdery mildew continue to be found in some blocks, but is likely not advancing at this time. Once temperatures become this hot and leaves and fruits develop thicker, waxy cuticles, apple scab and powdery mildew naturally become slowed. Fewer rain events help too.

Fire blight seems to be stopping its spread as trees slow their growth for the season. If we were to get hail or high winds at this time, it is likely fire blight would not spread rampantly as it can prior to early July and cover sprays would not be necessary in blocks that are clean of blight now.

Apple growers should have had at least one application on for summer diseases and a second application shouldn’t be needed for at least four weeks, if not even six weeks, after the first. Michigan State University Extension recommends fine-tuning your summer disease management by using the models on the MSU Enviro-weather website for the weather station nearest your location.

Tree fruit insects

Codling moth adult flight in high pressure blocks has finally dropped to zero or near zero. Egg hatch should be complete for first generation. A regional biofix for high pressure blocks was set for May 16 (250 growing degrees days base 50 from Jan. 1). GDD since biofix is 1,132. Cover sprays are not as crucial at this time in blocks below the threshold of five moths per trap per week. Lures should be changed soon in anticipation of second generation adult flight.

Codling moth adult flight in average/moderate pressure blocks ended in the last 10 days. Egg hatch should be complete for first generation. A regional biofix was set for May 26 (357 GDD50 from Jan. 1). GDD since biofix is 1,024. Cover sprays are not as crucial for the next two to three weeks in blocks below threshold. Lures should be changed in anticipation of second generation adult flight, which is likely to begin soon.

European red mites are beginning to build in some blocks. Continue to carefully monitor mite populations and the beneficials that attack them. The threshold is five mites per leaf for July and moves to 7.5 mites per leaf for August. Monitor for beneficials – one per leaf indicates wait a week and count again.

Obliquebanded leafroller adult flight has been ended for over two weeks, but small larvae continue to be found when they really should be all hatched. A regional biofix was set for June 12 (1,036 GDD42). GDD since biofix is 1,148. Continue to monitor for small larvae in terminals. Adults will begin to fly again soon. Lures should be changed in traps for the best monitoring.

San Jose scale second generation adult male flight is beginning. New crawlers should begin to emerge in the first week in August and that will be the next timing for control. This generation crawlers are more likely to settle on fruits, as well as limbs. Continue to monitor activity.

Oriental fruit moth second generation adults should be declining as flight comes to an end, but larval activity is at a peak right now and cover sprays are very important in stone fruits and perhaps apples with very high numbers. A regional biofix was set for May 6 (256 GDD45). GDD since biofix is 1,611. Expect second generation egg hatch to continue for at least another 10 days or until Aug. 6 or 7. Scout carefully for shoot flagging in stone fruits as well as fruit feeding. Third generation will be the one to watch for in apples, and you should be trapping for adult flight of oriental fruit moth in apples if you had unexplained worm damage in the bin last fall – it could have been oriental fruit moth rather than codling moth.

Some initial apple maggot flight was reported around the Ridge two or three weeks ago, but numbers are still quite low. We have more than met the degree-day requirements for their development into adults. A heavy rain event would likely drive them out of their overwintering soil sites. Continue to monitor.

Spotted wing Drosophila flight is reported throughout Michigan. This is not an issue for apples, but monitoring should be done in soft fruits, including cherries, peaches, plums and berries.

There have been no reports of brown marmorated stink bug egg hatch or nymphs in the Grand Rapids, Michigan, area.         

Very few Japanese beetles have been reported in the Grand Rapids, Michigan, area so far. Carefully monitor sweet cherries, raspberries and grapes – their favorite fruit hosts.

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