Grand Rapids area tree fruit update – April 30, 2019

The Michigan spring weather rollercoaster continues.

A week of slightly cooler than normal weather has kept tree development at a standstill. A few sweet cherries are starting to bloom, peaches need some time yet and apples are pretty much all in the tight cluster stage, give or take a little.

Degree day totals for the general west Michigan area are now tracking a few days behind a normal average. As of April 29, the Michigan State University Sparta Enviroweather station has accumulated 215 degree days base 42, which is five days behind the average from Jan. 1. Degree days base 50 at Sparta are 90, which is also about four days behind the normal average from Jan. 1. Forecasted temperatures look to be in the average range or even slightly below average for this time of year, so degree day accumulations will move at a normal pace as will tree growth.

Soils have dried out nicely and a good deal of tree planting got done last week. Rains moved back in for this week to slow that process down.

Tree fruit diseases

There have been several apple scab wetting events since the start of green tissue in apples, but none have resulted in apple scab infections and spore numbers have been very low to start the season. That most likely will change with rains that started Monday, April 29, and are predicted to continue much of the week. We would need 8 hours of drying time to end one wetting period and start another and given the forecast, it’s highly likely the rains will get strung together for one long infection—perhaps. My spore numbers took a huge leap with the rain that started in the morning on Monday. So far, I’ve counted 5,040 spores per rod on average.

Please visit MSU Enviroweather and click on the station nearest your orchards for further model details.

Tree fruit insects

Very little forward movement has happened in the world of insects. We are still waiting for some warmer weather to get the adult beetles of the black stem borer active. Traps should be in place soon if not already.

Red banded leafroller adult flight began about 10 days ago with very low numbers reported. Trap numbers are expected to increase over the next two weeks. This is another minor pest in tree fruits in the Grand Rapids area.

Spotted tentiform leafminer adult flight started 10 days ago as well with very low numbers found. This is a minor pest and management is only needed if damage was high the previous growing season.

A few small obliquebanded leafroller larvae can be found in terminals of apples. Pay close attention to blocks with higher pressure in 2018 as this pest seems to be increasing the past two seasons.

A few apple grain aphids continue to be found in very low numbers as a few individuals on terminals. Rosy apple aphids usually appear around pink.

Overwintering San Jose scale are present. Consider trapping for male flight in high pressure blocks of tree fruits. Adult males usually start to fly during apple bloom time.

No adult activity of oriental fruit moth yet. It typically happens around pink in apple. Traps and lures should be in place in the next week. Oriental fruit moth mating disruption pheromone can be put up at any time in stone fruits if pruning is done.

No reported codling moth adult flight, as expected. We usually start to catch a few in late bloom. Codling moth mating disruption pheromone can be put up at any time, but before bloom is best. Traps should be placed before petal fall.

European red mite is in the egg stage. No activity at this time, but egg hatch could begin at any time. Monitor for overwinter egg mortality; if eggs look pale or clear instead of bright red, they are not viable, and this is likely given the harsh temperatures we experienced in February and March.

No reports of tarnished plant bug activity in this area. Continue to monitor.

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