Grand Rapids area tree fruit update – July 14, 2020

Summer pest and crop concerns for apples.

Sunburn on apples
Sunburn on apples. Photo by Amy Irish-Brown, MSU Extension.

Weather update

Degree day accumulations put most of the Grand Rapids, Michigan, area at or slightly ahead of normal averages for mid-July. Soil moisture levels were very low until the rains from late last week brought us close to normal. Now after four or five days, soil moisture deficits are again a concern, particularly in areas that missed the heavy rains. You can track irrigation needs on Michigan State University Enviroweather, which is linked to the Cornell NEWA irrigation model.

Crop update

Apples continue to grow quickly with the warm temperatures and most fall in the 25- to 30-millimeter stage depending on variety and site. There continues to be variability in fruit set, some lighter than expected and some heavier—again, depending on variety and site. Sweet cherries had a very light fruit set and harvest is complete. Apricot harvest is also complete. Peaches have a very nice crop overall with some heavier or lighter depending cultivar and site. The earliest peach cultivar harvest is just beginning.

The extreme heat stress in the past week has led to a risk for early symptoms of sunburn and fruit skin damage. With very hot temperature in the near forecast, this again becomes an issue. Sunburn on apples is not a common issue in Michigan summers—our light intensity is much less than other arid growing areas out west. However, we do see some on some varieties and you may want to consider applying protective materials to prevent sunburn. Also, avoid summer pruning or applying reflective materials to the row middles immediately before a predicted period of high temperatures. Maintaining an adequate irrigation schedule helps prevent stress to lenticels, which can be damaged by the heat. Some useful information can be found in this MSU Extension article from 2013, “Sunscald and heat stress in apples could be an issue in the next week or two”

Tree fruit diseases

Fungicide applications to target summer diseases, sooty blotch and flyspeck, are needed in some areas. The wetting hours in 2020 for this model have been extremely variable, so be sure to check out the model online at MSU Enviroweather for information from the station closest to you to help with decision making as to timing for summer disease fungicides.

Continue to maintain a general protective fungicide program for any potential apple scab or fruit rots.

Tree fruit insects

First generation codling moth is coming to an end and only the high pressure blocks need to continue with cover sprays at this time. This is a good time to change out lures ahead of second generation flight.

Apple maggot have started to fly just as expected after the heavy rains last week. The best method to manage apple maggot is to trap individual blocks and apply cover sprays accordingly. You cannot ignore apple maggot just because you don’t trap for them.

Japanese beetles also made a pronounced arrival after last week’s rains. They are very active and will continue to damage all fruits for at least another four to six weeks.

Various species of aphids can now be found in all tree fruits, including green apple aphids and woolly apple aphid in apples, black cherry aphids in sweet cherries and green peach aphids in peaches. Warmer weather and rapidly expanding shoot growth are favorable for aphids. Beneficial insects such as ladybird beetle larvae, lacewing larvae and syrphid fly larvae are now easy to find in aphid populations.

Obliquebanded leafroller adult flight is winding down. Egg hatch is likely at a peak. Adequate scouting for small larvae is needed to determine the need for cover sprays.

San Jose scale crawlers are now present and should be addressed in blocks with high pressure.

Second generation adults of oriental fruit moth started to find their way to traps a week ago. Timing cover sprays to manage newly hatching eggs is again needed in stone fruits and perhaps young apple trees or nursery trees to prevent shoot flagging.

All stages of European red mite can now be found in apples. Twospotted spider mites are also being found. Mite populations have quickly grown this season with some bronzing already noticeable in poorly managed apple blocks.

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