Grand Rapids area tree fruit update – May 7, 2019

Rain and more rain for the general Grand Rapids, Michigan, area.

Overwintering San Jose scale on apple.
Overwintering San Jose scale on apple. Photo taken April 29, 2019, by Amy Irish-Brown, MSU Extension.

In the past week, heavy rains fell in most of the general Grand Rapids, Michigan, area, putting an end to tree planting for a while and resulting in a major heavy apple scab infection. Temperatures have stayed on the cooler than normal side and tree development continues to move very slowly, if at all. Sweet cherries are starting to bloom, as are early peach cultivars. Apples have been stuck in the tight cluster stage for over a week.

Growing degree day (GDD) totals for the general west Michigan area have fallen backwards with most areas being about a week behind normal averages for May 7. From Jan. 1 through May 6, the Michigan State University Sparta Enviroweather station has accumulated 270 GDDs base 42 and 195 GDDs base 50.

Forecasted temperatures look to be in the average range or even slightly below average for this time of year, so GDD accumulations will move at a normal pace and tree growth will continue to be slow. Perhaps apples will get to the pink stage by the end of this week and some early bloom by early next week.

Tree fruit diseases

There was one major apple scab wetting event last week with many area weather stations seeing nearly 100 hours of wetting between April 29 and May 3. Spore numbers were the highest yet for the 2019 season with a total of 5,184 for the entire wetting period. Lesions from this major infection should show up in 10 to 15 days and scouts will need to be looking carefully for them as the potential is high that some infection creeped through.

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

Tree fruit insects

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

Spotted tentiform leafminer adult flight continues in very low numbers overall. Spotted tentiform leafminer is a minor pest and management is only needed if damage was high the previous growing season.

I continue to see and hear reports of low numbers of small obliquebanded leafroller larvae found in terminals of apples. Monitor all blocks, but especially those 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 should appear any day.

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, which could be any time. It is best to place adult male pheromone traps near known scale infested trees or limbs. They do not fly very far and can be difficult to trap effectively for.

There has been no adult activity of oriental fruit moth. They are expected to show up in the next week or 10 days. Traps and lures should be in place now to get an accurate biofix. Oriental fruit moth mating disruption pheromone can be put up at any time in stone fruits if pruning is done.

There has been 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 still in the egg stage with no hatch reported. We need a little warmer weather and eggs will likely hatch quickly.

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