Grand Rapids area tree fruit update – Sept. 3, 2019

As harvest begins, be mindful of late-season insects and diseases.

Early apple harvest on the Ridge
Early apple harvest on the Ridge. Photo by Amy Irish-Brown, MSU Extension.

Rainfall continues to be quite adequate for the general Grand Rapids, Michigan, area. While there are dry spots that might still need irrigation, most areas have had ample rain. In fact, I can’t remember a year when mushrooms have been present in my lawn all summer long as they have been this year. As some early apples are now being harvested, it’s becoming apparent the Michigan State University Extension predicted apple harvest dates for 2019 are falling in line as we estimated. Don’t rush to harvest until maturity parameters are met. The cooler nights and bright sunny days are perfect for coloring fruit, but starch and brix, pressures and internal ethylene are moving slowing for most apple varieties.

Degree days for Jan. 1 through Aug. 19 for the MSU Sparta Enviroweather station are 3,103 degree days base 42 and 2,029 degree days base 50. These totals are two days behind normal average degrees for the Sparta Enviroweather station based on 40 years of comparison data.

Tree fruit diseases and late-season hail

There was some hail that moved across Fremont and the Ridge last week. Damage ranged from extreme cuts on apples to a few dents. At this late date, there should be no risk of fire blight spreading, even if it is already present in these blocks. Fruit rots could be an issue if the skin was broken and fungicides can help if the damage was not too severe and fruit can still be harvested for processing. Hopefully the storms moving into our area today, Sept. 3, 2019, will not have any more hail in them.

In unmanaged apples, apple scab has started to show up as new lesions on leaves and fruits over the past 10 days. If you have primary scab present, you need to keep a good fungicide cover on to protect fruits from now until harvest from further apple scab infections. Any rain event lasting longer than six hours will be enough to cause additional secondary scab infections.

Sooty blotch and flyspeck should be of concern in areas with heavy rainfalls. Another fungicide cover prior to the busy time of harvest may be necessary, given all the wet conditions lately. The fungicides you use for summer disease should help with fruit rots as well, which we could see higher pressure for this summer and fall.

Tree fruit insects

Second generation codling moth adults should be past their peak egg laying stage and trap numbers of adults have declined in the past week. Egg hatch will continue for at least another two weeks in blocks under heavy pressure and good cover sprays are needed to protect from fruit stings. Using the original Grand Rapids regional biofix of May 25, 2019 (237 DD50), there have been 1,792 degree days base 50 accumulated since then, which indicates second generation egg hatch is past peak and should begin to decline.

Hot spots continue to have very high numbers of apple maggot adults caught on red sticky traps. Many blocks are not catching any, but there are blocks with very high pressure. Cover sprays now need to be maintained to prevent egg laying stings in all apples where traps are still catching. This is a sporadic pest lately and not all orchards need to cover for it, but you don’t know your population if you aren’t trapping properly for it. Traps should be placed along wooded areas if possible. The best traps are the red spheres with apple essence added.

Reports of damage due to brown marmorated stink bug are very light so far for 2019 across all of Michigan. Trap numbers have not spiked as is typical in late August. Very few adults and nymphs can be found. I have been walking through a few soybean fields recently looking for brown marmorated stink bug and they don’t seem to be present in beans as is usual. Perhaps the winter was hard on them as it was on some Fuji and Gala trees. Or, maybe there are some beneficial organisms at work out there. It’s a bit of a head-scratcher, but the MSU monitoring team will keep checking traps until Oct. 1 and will let you know if we see an increase in numbers.

The rapidly expanding shoot growth in the summer months was very favorable for green apple aphids. There are still populations present, but they are declining and no longer need management. We continue to find high numbers of beneficials present in most aphid populations – syrphid fly larvae and ladybug larvae and adults are common. While there are some woolly apple aphid present in apple canopies again this fall, it does seem that they are less than 2018 and perhaps all those beneficials are helping.

The second generation crawlers of San Jose scale have now settled down on fruits and are starting to reach the black cap stage where pesticides won’t work well against them. Using the original regional biofix date of May 25, 2019 (211 DD51) we have accumulated 1,695 degree days base 51, which indicates second generation is complete and a third generation could be starting. MSU experts believe the high numbers of San Jose scale in recent years are due to a third generation and research is underway to explore this further.

Japanese beetles are still around and numbers seem to be dropping off quickly.

Third generation oriental fruit moth egg hatch should be winding down. From the regional biofix date of May 17, 2019 (288 DD45) the Sparta Enviroweather station has accumulated 2,392 degree days base 42, which puts the end of generation three egg hatch on Sept. 10. Often, several generations of oriental fruit moth begin to overlap in the summer, making it hard to judge coverage needs. If you are catching 30 to 40 moths per week in a peach block, you have high pressure. Traps in apple blocks can tolerate higher levels before fruit damage becomes a concern.

All stages of European red mite can be found, and in some blocks, numbers have exploded and bronzing is easily noticeable. Twospotted spider mites are also present. Once we get past Aug. 15, it’s usually not economically worth it to put on a miticide. Now that we are into early September, it’s best to let the populations go and hopefully some beneficials can build to help curb populations in 2020.

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