Grand Rapids area tree fruit update – May 14, 2019

Apple trees are moving nowhere fast.

Apples in the pink stage
Apples in Sparta, Michigan, in the pink stage. Photo by Amy Irish-Brown, MSU Extension.

Continued cooler than normal weather has many tree fruits stuck in the same stage for the past 10 days. Apples are getting to the open cluster or pink stage overall with a few blooms opening recent days on early cultivars. Sweet cherry and peaches are nearly in full bloom. Warmer weather predicted for later this week will be very welcomed not only by humans, but for trees as well. Pale foliage as a result of growth and nitrogen movement in trees will turn around as soon as some warmth hits us. Tree planting will resume as soon as soils dry out a bit more.

Degree day totals for the general west Michigan area have fallen backwards with most areas being about a week to 10 days behind normal averages for May 13. From Jan. 1 through May 6, the Michigan State University Sparta Enviroweather station has accumulated 336 degree days base 42 and 133 degree days base 50. Forecasted temperatures are going to be much warmer than we’ve had, but still within average range for this time of year, so degree day accumulations will move at a normal pace and tree growth will move at an even pace and not too quickly. Many apple varieties will move into bloom by the weekend.

Tree fruit diseases

There were several wetting events over the past week, and they were quite variable depending on which of the 13 weather stations around Grand Rapids, Michigan, you are following. Some very high apple scab spore numbers were collected indicating we should be at about 50% spore discharge with more to mature and discharge in the near future. Rains predicted for this week should be covered well for with your fungicides as we are right in the height of apple scab for 2019.  

Typically, during pink to petal fall is when mildewcides need to be added in susceptible apple varieties to prevent initial infections of powdery mildew. The weather so far this spring has not been favorable for mildew, but now is the time to add fungicides for mildew as leaf tissue is expanded and future apples are exposed, and some warmer weather is near.

As bloom begins to open and warmer weather moves in, the concern for fire blight of blossoms should come to the forefront of your spray program. There are four parameters according to the MaryBlyt model for a full infection to occur: open, viable bloom, EIP near or over 100, average temperatures over 60 and a wetting event. All four are likely to occur in the next week or two.

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

Tree fruit insects

Insects continue to be too slow to be active with cooler weather. Very little forward movement has happened in the world of insects. If you haven’t put your pink spray on, you might still have time to do it on all but the earliest cultivars of apples that are showing some open bloom. No insecticides are to be used during bloom if they have the potential to harm bees. Honey bee hives have been not very happy with this cooler weather either, but they should have something to work on soon.

We are still waiting for some warmer weather to get black stem borer adult beetles active. Traps should be in place soon if not already.

Spotted tentiform leafminer adult flight continues now for about the fourth week 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 in apple terminals. 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 are also beginning to be active, but you must look hard to find them.

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

There has been no adult activity of oriental fruit moth, and they should become active with the warmer weather in the next few 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 anywhere in Michigan, and warmer weather should get them active in more southern areas of the state. I expect them to begin early flight in the Grand Rapids area in the next 10 to 14 days. 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 for codling moth 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. Petal fall sprays will target this pest well.

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