Grand Rapids area tree fruit update – June 21, 2022

Tree fruit is continuing fruit sizing, with most apples between 20-25 millimeters. Hot weather is expected this week.

Tree fruit.
Tree fruit in Sparta, Michigan, on June 21. Photo by Anna Wallis, MSU Extension.

Weather and phenology update

Over the past week in the Grand Rapids area, conditions were cooler than normal and dry. High temperatures for most of the week were in the low 70s (F) and overnight lows in the 40-50s. As of June 13, the Michigan State University Sparta Enviroweather station has accumulated 1040.5 degree days base 42 F (DD42). This is slightly above average, which is 986.4 DD42, and approximately two to three days ahead of normal.

It was a very dry week. On Wednesday, approximately 0.25-0.35 inches of accumulation was recorded in most locations, followed by no precipitation for the remainder of the week through the weekend. Overnight Monday, most weather stations received nearly an inch of rainfall.

Tree fruit is continuing to size. A very good potential crop is setting well in most locations. Most varieties of apples are between 20-25mm. Earlier blocks and varieties such as Ginger Gold and Zestar are beyond 30mm. Peaches and cherries are continuing to size as well.

A heatwave is being experienced across the Midwest this week, and excessive heat is forecasted for most of Michigan for the next two days. Expect hot and humid conditions, with highs in the upper 80s to low 90s. Scattered showers and thunderstorms are possible overnight Wednesday. This will be followed by slightly cooler, dry conditions through the weekend with highs in the mid to upper 70s, and then a return to very hot conditions. Dry weather will continue through the weekend, with the next chance of precipitation at the beginning of next week. Hot, dry weather will be coupled with high potential evapotranspiration (PET) this week and next, leading to an unusually high water demand across the region.

Degree day accumulation at Enviroweather stations in the Grand Rapids area

Weather Station Degree Days Base 32 from Jan. 1 Degree Days Base 42 from Jan. 1 Degree Days Base 50 from Jan. 1
Aetna - Fremont 2041.4 1200.5 712.3
Alpine 2168.9 1288.7 775.8
Belding 2129.3 1266.7 769.8
Clarksville (CRC) 2186.1 1296.4 784.3
Conklin 2151.6 1274.8 759.3
Fremont 2084.3 1230.9 740.5
Grant 2089.1 1228.1 734.3
Kent City 2092.4 1235.6 740.2
Reeman-Fremont 2082.6 1223.1 727.9
Sparta 2114.8 1249.1 748.2
Sparta 20m Tower 2127.9 1256.1 751.2
Sparta - North 2134.1 1263.9 757
Standale 2227.7 1325.9 807.4
Average DD from Sparta historical data for Jan. 1 to date 2061.5 1151.4 653.1
Comparative Date of Averages @ Sparta 22-Jun 24-Jun 26-Jun
Days +/- Average @ Sparta + 2 days + 4 days + 6 days

For these updates, we used averages for 1997-2021 from the Michigan Automated Weather Network (MAWN) to represent normal conditions. Weather data was gathered from MSU Enviroweather.

More information and reports on normal weather conditions and departures from normal can be found on the NOAA Climate Prediction Center website, NOAA U.S. Climate Normals website, NOAA Climate Normals Quick Access Page (which may be searched by region) and Midwest Regional Climate Center website.

Tree fruit diseases

Primary apple scab continues to be a potential until we get a rain event with zero spores. The forecast isn’t going to give us that rain any time soon. I did catch an average of three spores per rod with the June 16 rain event, so this is still a primary scab infection for any areas that had enough hours of wetting. There is some apple scab showing up in managed McIntosh blocks, and many other varieties are clean. Macs are just so susceptible. I am also seeing and hearing about a bit of fruit scab where no leaf scab seems to be present. This is unusual, but not unheard of. Careful scouting is needed from now until the end of June to be sure no primary scab got through.

Overall, fire blight risk is lower now that bloom is over and in the general Grand Rapids area, and most blocks look really clean of blight. If you do have blight showing up, remove it ASAP and continue a strong management program to keep it from spreading further. There are a few reports of blight in blocks with a history of this disease.

Powdery mildew is present more this year than expected. Peach leaf curl is more prevalent as well, likely due to the ideal cool and wet conditions at bud break that favor this pathogen.

Tree fruit insects

Codling moth adult flight continues to be variable with the ups and downs in the evening temperatures. A Grand Rapids regional biofix was set for May 15 (254 GDD50) with 520 degree days base 50 accumulated since then. In general, this area should be at peak egg hatch and management programs should be in place to prevent fruit damage.

A regional biofix for obliquebanded leafroller was set for June 14 and there have been 244 degree days base 42 accumulated. This indicates we are in peak moth fight and early egg hatch will occur early next week.

First generation oriental fruit moth flight and larval activity is ended. Second generation adults will hit traps soon and this is a good time to change our lures.

Green apple aphids are becoming common on young growing terminals. There are also several predators in these populations. Woolly apple aphids are also present, having overwintered in the canopy in some blocks or having now started to crawl up from their root feeding sites.

Very few male San Jose scale continue to be caught in pheromone traps—they seem to be very late or very low in number this year. A regional biofix was set for May 15 for the general Grand Rapids area with 460 degree days base 51 accumulated since then. First crawlers started to be found about a week ago. Timing for systemic materials is nearly past for effective control, and the window for contact materials is starting.

European red mite can be found in all stages – adults, nymphs and eggs. Predatory mites are also being found in European red mite populations. There are a few twospotted spider mites in some areas. Continue to monitor for all mites. Petal fall miticides are likely no longer effective and with the extreme heat and dry conditions on tap for this week, mite populations could get out of hand really quickly.

White apple leafhopper and potato leafhopper are now present in all life stages. Be sure to keep an eye on newly planted trees for high leafhopper and aphid populations that could curb shoot growth unexpectedly.

Beneficials observed on orchard visits include ladybug beetles (adults and larvae), syrphid flies (adults and larvae), beneficial mites, chiggers, ground beetles, earwigs and robber flies.

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