Grand Rapids area tree fruit update – Aug. 6, 2019

Soils are getting dry—from feast to famine.

Weather and crop update

July brought varying amounts of rainfall across the area, totaling 1.5 inches to nearly 4 inches depending on the location. There has not been significant measurable rainfall now for 14 days and soils are really beginning to dry out and as we move into August. Rainfall can be scarce and supplemental irrigation will continue to be necessary.

All tree fruits are sizing nicely, and tree growth has been very good this year. Most apples now have terminal buds set, which is a good thing.

Local meteorologists are reporting that July was 2.3 degrees above normal and that has really pushed our degree day totals forward. We have caught up to normal averages for early August for the general west Michigan area. From Jan. 1 through Aug. 1, the Sparta Enviroweather station has accumulated 2,295 degree days base 42 and 1,475 degree days base 50.

Phil Schwallier has written an article with predicted apple harvest dates for 2019, which has more cultivar details than the Enviroweather site lists.

Upcoming meeting on applying ReTain

In preparing for harvest, you will need to begin applying ReTain soon. There is a virtual meeting at 12 p.m. on Aug. 8 that’ll discuss the ReTain label change, application timing and how it relates to current weather we’re experiencing. See more details below. 

Who should join: Apple growers, retailers, Valent U.S.A. and MSU Extension educators and specialists
Where: Skype meeting on phone and/or web broadcast
Why: Learn techniques to increase apple quality/packout with ReTain manage harvest timing. 
How to join: Click “Join Skype Meeting” to attend virtually, or join by phone by calling +1-213-336-0340. Conference ID: 35006826#. Trouble joining? Try Skype Web App

  • Welcome Message – Jeff Schulz, Valent U.S.A. (host)
  • Introduction to ReTain – Gregory Clarke, Valent U.S.A.
  • Regional Observations and Local Recommendations – Phil Schwallier, MSU Extension
  • Questions/Comments from participants

Tree fruit diseases

The drier weather and waxy leaves and fruits have slowed down the spread of apple scab, but if you have scab, you need to stay covered for any rain event that might last longer than 6 hours. As we move into potentially wetter conditions in late August and September, leaves and fruits will become susceptible to scab infections again and you will want to keep your protectant fungicide rates tight.

The stormy weather a few weeks ago didn’t seem to get fire blight moving. It certainly helped that trees were slowing down and that growers did an excellent job of keeping early fire blight infections away. In August, if we were to get storms or hail, only blocks with recent history of fire blight would need to be protected. If you find fire blight in your blocks, it is best to cut it out if the strikes are relatively few.

Summer diseases like sooty blotch and flyspeck could need follow-up fungicides if you received more than 2 inches of rain since your previous summer disease application. Add another 200 or so hours of wetting after that 2 inches of rain and these fungi could start to express again as sooty blotch and flyspeck on fruits.

Tree fruit insects

First generation codling moth activity ended about 10 days ago with second generation flight beginning pretty quickly after. We are now reaching the timing for early egg hatch for second generation in high pressure blocks and cover sprays are again important. Many blocks saw a break in adults in traps. You can set a second biofix and use that for decision-making on a block-by-block basis. I am hearing of quite a few blocks with continued adult flight, so I’m going to stick with my original regional biofix of May 25 (237 GDD50). There have been 1,275 growing degree days (GDD) base 50 accumulated since then, which indicates early egg hatch could be starting.

All eggs of the first generation of obliquebanded leafroller adults should be finished hatching. Trap numbers of adults are increasing as the summer flight reaches a peak. I set a regional biofix for June 17 (970 GDD42) and there have been 1,324 GDD base 42 accumulated since that date, which indicates the summer adults should be at peak flight now and egg hatch of the overwintering generation will begin soon. There are some hot spots on the Ridge with rather high numbers of obliquebanded leafroller in them. Nothing like 15 years ago, but still higher than we’ve seen in recent years.

Apple maggot flight continues in normal numbers. I would expect a good rain would really push more maggot adults out of their overwintering sites in the soil. Cover sprays should begin next week after the rains predicted for Monday into Tuesday if you haven’t started already. Red sticky sphere traps are preferred, and apple essence should be used to get an adequate trap catch for decision making.

The expanding shoot growth in June and July has been very favorable for green apple aphids— they’ve exploded in the last month! There are lots of beneficials present in most aphid populations I see—syrphid fly larvae and ladybug larvae and adults are common. There are also woolly apple aphids present in apple canopies and management should be considered now in blocks with high pressure in 2018. Hopefully the abundance of beneficials will curb the woollies as well.

Frist generation San Jose scale crawlers are now settled in with a good waxy shell in place, making them more difficult to manage effectively. Second generation adult male flight is beginning. Using the original regional biofix date of May 25 (211 GDD51), we have accumulated 1,175 degree days base 51. This model indicates that crawlers of the second generation will again be present around Aug. 15 and management should be targeted again at that timing.

Second generation oriental fruit moth egg hatch should be just past its peak and not wind down until about Aug. 12 or 13. From the regional biofix date of May 17 (288 GDD45), the Sparta Enviroweather station has accumulated 1,680 degree days base 42. Often, several generations of oriental fruit moth begin to overlap in 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. Threshold for all mites is 7.5 mites per leaf for August.

All stages of white apple leafhopper and potato leafhopper can now be found. Numbers are not high, but you can find them in just about every block you look in.

Brown marmorated stink bug damage has been reported occasionally in apples over the past month. We think much of this feeding is exploratory feeding by overwintering adults as they move across an orchard seeking better food choices. By the time the damage becomes visible, brown marmorated stink bug has long moved on and are no longer in the orchard. There are some nymphs starting to be found in traps in low numbers. Once you trap nymphs, consider management in blocks with a history of brown marmorated stink bug damage.

Japanese beetle activity continues with leaf skeletonizing in all tree fruits being seen. We are likely in for at least three more weeks of activity, if not longer.

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