West Michigan tree fruit update – June 19, 2018

Primary apple scab is over for 2018.

Tree fruit diseases

No spores were caught with the rains on June 16 or 18, so it appears primary apple scab is over for the 2018 season. There is some scab showing up in blocks, mostly the most susceptible varieties, so continue to monitor closely for scab and keep full fungicide rates on these blocks. Clean blocks can reduce scab fungicides to summer rates.

Very little fire blight strikes are being seen in the Grand Rapids, Michigan, area. Keep an eye on the weather for any storm fronts that might bring hail or high winds. Trees are still very much susceptible to trauma blight until we get to terminal bud set in July.

Apples are still susceptible to powdery mildew and high relative humidity conditions will greatly favor mildew. It’s a bit early for summer disease cover sprays—they will most likely not be needed until mid-July, depending on rainfall and heavy dews of course.

Tree fruit insects

Plum curculio adult egglaying activity should be over for 2018. Continue to monitor along woodlots for recent damage.

Codling moth adult trap numbers have seemed to have leveled out. We should be nearing peak egg hatch and cover sprays are critical. A regional biofix was set for May 25 (313 GDD50) with 481 GDD50 accumulated since then. Peak egg hatch is expected by the weekend (June 22-23). Cover sprays are critical in blocks over a threshold of five moths accumulated per trap for first generation.

Spotted wing Drosophila numbers are very low to no adults in traps this past week. With cherries in straw color or red stages, consider cover sprays as fruit might ripen quickly. Watch per-harvest intervals for various pesticides used. Continue to trap for flies in ripening crops, especially cherries.

Obliquebanded leafroller adult flight is more regular, but numbers are not high overall. We should be nearing a peak adult flight now. A regional biofix was set for June 11 (1,042 GDD42) with 239 GDD42 accumulated since then for the Sparta Enviroweather station. Peak adult flight is about a week away. First egg hatch is expected in the last week of June, around June 26—this is the timing for high pressure blocks. In low pressure blocks, scout for larvae and spray if needed, perhaps just after the Fourth of July.

San Jose scale male flight should be completed for this first generation. No crawlers have been found in Grand Rapids—they should appear any time. A regional biofix was set for May 25 (286 GDD51) with 456 GDD51 accumulated since then. Systemic sprays need to go on now to be taken up and in sap for crawler feeding. Contact sprays can go on a week later, approximately June 25-27.

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

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

A few spotted tentiform leafminer mines are being reported and second generation adults are flying. This pest is of very little concern in orchards these days.

Brown marmorated stink bug adults seem to be higher in numbers this spring than ever before. This might be the year to not ignore brown marmorated stink bugs any longer. Continue to monitor and begin to form a plan for managing this new pest if you are seeing more than last year.

Second generation oriental fruit moth adult flight should begin to pick up in numbers soon in the Grand Rapids area. This is a good time to change out lures. A regional biofix was set for May 10 (272 GDD45) with 812 GDD45 accumulated since then. Scout carefully for damage from first generation in stone fruits. New larvae from the second generation should appear in a week or so with cover sprays becoming important again the first week of July in stone fruits.

American plum borer, lesser peachtree borer and peachtree borer are all flying. Apply trunk sprays in stone fruits before the end of June. Dogwood borer flight just started in the Grand Rapids area. Dogwood borer trunk sprays are best timed for around July 4 for chlorpyrifos—earlier if using other materials.


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