Grand Rapids area tree fruit update – May 24, 2022

After a record-setting warm week, expect a return to cooler than normal conditions.

Tree fruit.
Tree fruit in Sparta, Michigan, on May 23, 2022. Most apple varieties are beginning early fruit sizing, with diameters between 4-6 mm. Stone fruit is at shuck split stage. Photo by Anna Wallis, MSU Extension.

Weather and phenology update

The past week was much cooler in the Grand Rapids, Michigan, area, especially compared to the heatwave the week before. High temperatures were mostly in the 50s and 60s (degrees Fahrenheit), with overnight lows in the 40s. It was slightly warmer at the end of the week, with a high of 84 F on Friday. As of May 23, the Michigan State University Sparta Enviroweather station has accumulated 598.7 growing degree days base 42 F (GDD42). This is slightly above average, which is 587 GDD42, and approximately one day ahead of normal.

Conditions were much wetter than the preceding week. Weather stations across the Grand Rapids area recorded approximately 0.5-1.0 inch of rainfall accumulation. Most of this occurred over Friday night and Saturday. Some areas were considerably drier, including much of west central region, where less than 0.1 inch of precipitation was recorded in some places.

The cooler weather slowed phenological development considerably. Most tree fruit is nearing the end of bloom, with some blossoms still open in later blocks and varieties. For most varieties of apples, late bloom and petal fall has been drawn out over last week and the beginning of this week. Early fruit sizing is beginning, with most fruit between 4-6 mm in Gala, Fuji and Honeycrisp. Earlier blocks and varieties such as Ginger Gold and zester are nearing 10-12 mm. Peaches and cherries are at shuck split and beginning early fruit sizing as well.

Expect mild, mostly sunny, dry conditions Tuesday, with clouds moving in overnight. The remainder of the week will be cool and wet. A low-pressure system will move into the area from the southwest on Wednesday, persist through Thursday, then begin tapering off by Friday. Steady precipitation and windy conditions are expected, with high temperatures in the 60s.

After this week, expect a return to warm, dry conditions. Temperatures will return to the upper 70s and low 8’s by the end of the weekend, and last through the beginning of next week. This is likely to coincide nicely with 8-10 mm fruit sizing and offer an excellent opportunity for thinning.

Degree day accumulation at Enviroweather stations in the Grand Rapids area

Weather StationDegree Days Base 32 from Jan. 1Degree Days Base 42 from Jan. 1Degree Days Base 50 from Jan. 1
Aetna - Fremont 1134.2 573.2 301.4
Alpine 1221.3 621.1 328.9
Belding 1183.1 600.4 320.5
Clarksville (CRC) 1229.2 619.5 326.9
Conklin 1205 608.2 314.5
Fremont 1155.2 581.8 308.9
Grant 1180.3 599.2 320.5
Kent City 1164.9 588 311.7
Reeman-Fremont 1156.5 576.9 301.5
Sparta 1184.2 598.4 316.7
Sparta 20m Tower 1195.7 603.8 318.5
Sparta - North 1195.1 604.8 319
Standale 1275.6 653.8 353.1
Average DD from Sparta historical data for Jan. 1 to date 1231 587.8 288.6
Comparative Date of Averages @ Sparta 23-May 24-May 25-May
Days +/- Average @ Sparta 0 days +1 day +2 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.

Pest update

As bloom comes to an end, we turn to the very important petal fall application to manage a great number of pests. Plum curculio hasn’t been too active lately with cooler weather in place, but they are expected to make a big appearance in all tree fruits soon. The forecasted temperatures for May 26 through June 2 will be very favorable for plum curculio egg laying.

Codling moth adult flight has been steady in some blocks and no flight in others. A Grand Rapids regional biofix was set for May 12 (312 GDD45), but there are some that should have an earlier biofix and others with a later date. Codling moth flight seems to be highly variable this season. The GDD accumulation since the regional biofix is 164. This indicates the time for materials that have egg activity. Early egg hatch covers are likely for June 2, 3 and 4.

Obliquebanded leafroller larvae are mostly rolled up in leaves with pupation occurring. Cover sprays won’t work well at this stage, so save them for the summer generation larvae.

Oriental fruit moth adult flight continues. Grand Rapids regional biofix was set for May 12 (312 GDD45) with an accumulation of 164 degree days since. Early egg hatch should be underway and cover sprays are needed in stone fruits. Peak egg hatch likely first week of June.

Various species of aphids can be found quite easily in various tree fruit species. Apple grain aphids have declined or moved on to other hosts. Rosy apple aphids are present, rolled up in terminals. Woolly apple aphids are present in tree canopies where they appeared to have overwintered.

San Jose scale initial male flight has been reported in the Grand Rapids area and trap numbers are very, very low still. I am waiting for sustained catch to calculate a biofix date. This pest rarely requires whole orchard applications to manage in apples. Careful scouting is key to identify hot spots to target spray.

European red mite eggs and first nymphs are present. Predatory mites are also starting to be found in European red mite populations. PF sprays will be important for European red mite this year.

Heavy and prolonged rainfall led to at least one apple scab infection across the Grand Rapids apple growing region. Some weather stations had two infection events. We are closing in on having all primary apple scab spores matured and then will need two or three rain events to release them all. Keep primary apple scab fungicide rates in place for at least two more weeks.

The last 10 days with open bloom increased the risk for blossom blight from the fire blight bacteria. Cooler weather this week lessened the risk. Even with most apple bloom coming to an end, there are some varieties that have rag tag bloom on 1 year old wood, and this will need fire blight protection with warmer weather moving back in next week if bloom is still present. Newly planted trees are out of sync in their bloom so pay attention to those trees during the hot spell coming up next week.

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