MSU Extension Fruit & Nuts

Horticultural concerns

Apple are sizing nicely with overall variety fruit size being right on target or slightly larger than models predict. Hand-thinning continues in some blocks. The potential for sunburn in apples continues to be a concern with the return of very hot weather this week. Some sunburn symptoms are already being reported, which is much earlier than we normally see it. In high value varieties that are highly prone to sunburn (especially Honeycrisp), consider protectant materials, keeping in mind that once you start applying them, continue applying season long.

The Grand Rapids, Michigan, area has not had the rains the south and north have seen, so the need for irrigation is of concern. The graph below shows the irrigation needs of apples using data from the Michigan State University Sparta Enviroweather station as of July 8, 2018. The Network for Environment and Weather Applications (NEWA) apple irrigation model indicates apples need another 1 acre inch of water in seven days. Trees have used 1 acre inch up to today. This model fits Standale, Belding, Sparta, Kent City, Grant and Fremont, Michigan.

Tree fruit diseases

Brown rot in sweet cherry has been a challenge this year with high temperatures, high relative humidity and a few heavy rain events that caused cracking that allowed brown rot a place to establish.

Summer diseases in apples include a complex of pathogens and the primary concerns are sooty blotch and fly speck. Most Grand Rapids area Enviroweather stations are totaling over 200 hours of wetting accumulation. This indicates it is time to add something in the tank to manage summer diseases and prevent their expression on the fruit surface which would make fruit undesirable for fresh sales.

Tree fruit insects

Adult trap numbers of codling moth have declined as first generation flight comes to an end. We should be nearing the end of egg hatch. A regional biofix was set for May 25 (313 GDD50) with 904 growing degree-days (GDD) base 50 accumulated since that date using Sparta Enviroweather data. Cover sprays are now becoming less critical unless you have blocks that are high pressure with more than five moths per trap still being caught per week. Adult flight for second generation could pick up in a week or so—this is a good time to change out lures.

Spotted wing Drosophila (SWD) traps continue to be very low, but some have recently shown an uptick. If you still have cherries hanging, they should be getting insecticide covers to protect from SWD infestation. Watch pre-harvest intervals for materials used near harvest. Pressure from SWD was much lower this year in the Grand Rapids area, but vulnerable crops still need monitoring, including peaches, apricots, summer raspberries and blueberries.

Obliquebanded leafroller adult flight should be declining, but will pick up again in a week or so for the summer generation flight. We should be past peak egg hatch and small larvae are becoming easier to find. A regional biofix was set for June 11 (1,042 GDD42) with 822 GDD base 42 accumulated since then for the Sparta Enviroweather station. Models predict all eggs to be hatched around July 15. Cover sprays for blocks with easy to find larvae are highly encouraged. As codling moth covers are nearing an end, don’t stretch obliquebanded leafroller covers too much; Bt is a great add-in with all the warmer than normal weather of late.

San Jose scale crawlers are settling down and forming waxy covers. A regional biofix was set for May 25 (286 GDD51) with 860 GDD base 51 accumulated since that date for Sparta. There is still a little time to get covers on for San Jose scale crawlers, but the window on first generation is closing fast.

Apple maggot flies on red sticky spheres in the Grand Rapids area have been reported in the last week. The heavy rain on June 27 seemed to have got them moving from overwintering sites in the soil. If you are catching them on red spheres, cover sprays need to begin within seven days of capture to avoid fruit damage. Early ripening varieties and red strains would be most vulnerable at this time.

The recent heavy rain really drove Japanese beetles from overwintering sites in the soil. Numbers are quite high in some areas. Continue to monitor as they most likely have not hit a peak yet.

All stages of European red mite and twospotted spider mite are now present. Some off-color and bronzing in trees is now noticeable. Predators are also present. Threshold for all mites is five mites per leaf for July.

Second generation oriental fruit moth adult flight should be nearing a peak in the Grand Rapids area. A regional biofix was set for May 10 (272 GDD45) with 1,336 GDD base 45 accumulated since that date. Cover sprays in stone fruits will be critical as we approach peak hatch around July 15. Second generation activity will continue through the end of July.

We are starting to see a few more aphids building in some blocks. Continue to scout for all aphid species and be on the lookout for predators.

All stages of white apple leafhoppers can now be found, but in very light numbers. Continue to monitor, paying close attention to nonbearing apples where cover sprays are less and populations can build and reduce growth.

Brown marmorated stink bugs can be found on various favored hosts in all stages. Overwintering adults seemed to be higher in number this spring than ever before. Some initial damage in weak trees was found in the last week due to exploratory feeding. Continue to monitor closely, particularly yellow apple varieties and Honeycrisp, which seem to be favorites. Cover sprays in high pressure areas should begin with second generation codling moth spray timing in early August.

Dogwood borer flight should be just past a peak and trunk sprays need to go on right away in high pressure blocks if not done already.