MSU Extension Fruit & Nuts

Weather update

The temperature is hot today, June 21, with temperatures in the 90s across the region. The rest of the week will be cooler with highs in the upper 70s and low 80s. Fruitlets continue to grow steadily (Photo 1) with warmer temperatures.

Based on the Hart Enviroweather station for June 21, current growing degree day (GDD) accumulation is 1,124 GDD₄₂ and 654 GDD₅₀. Accumulation of GDD has increased by about 200 GDD₄₂ and about 140 GDD₅₀ over the past week. Degree day accumulation is similar to the five-year average (Table 1).

Conditions are dry throughout the region. We had little rain and warm temperatures over the past few days with windy conditions. Warm and dry conditions will continue over the coming week. There is a slight chance of rain this weekend, but showers will be scattered. Growers may need to irrigate this week, especially for young or newly planted orchards.

*Averages were calculated using data from 2020-2021.
**Averages were calculated using data from 2018-2021. 

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.

Crop update

Fruitlets continue to grow, and June drop is almost finished for many varieties. Growers can decide if hand thinning will be required for apples and peaches. Sweet cherries are turning red, and tart cherries are beginning to develop a red blush.

Apple varieties in the west central region are being monitored, and fruitlet diameter increased by 4-6 mm over the past seven days for many varieties. In Oceana County, fruitlet diameters range from 24-27 mm for Gala, 30-35 mm for Honeycrisp, 28-32 mm for McIntosh and 30-33 mm for Jonagold. Predicted harvest dates are now available from MSU Extension.

Tart and sweet cherry fruit diameters range from 15-20 mm. Some sweet cherries are developing red color and may begin to be fed on by birds. Across the region, tart cherries have developed a red blush, and many growers are considering when to apply Ethrel before harvest.

Peach fruitlets are sizing well. Fruit diameters range from 27-31 mm. Growers should evaluate if thinning will be needed. Venture peaches will be hand thinned at the West Michigan Research and Extension Center this week.

Pear fruit diameters range from 24-26 mm. Fruitlets are sizing well, and clusters have thinned down to one or two fruit per cluster.

Pest and disease update

In the west central region, continue scouting blocks to target hot spots for active pests in the orchard according to growth stage. Warmer weather has advanced pest activity. Green peach aphid and green apple aphid were spotted in the region. Also, rose chafer was observed on apple on June 20. Low trap numbers were observed for oriental fruit moth, codling moth, dogwood borer, and lesser apple worm on June 20. Two adult obliquebanded leafrollers were also trapped this week. In addition, lesser peach tree borers were trapped at the West Michigan Research and Extension Center this week.

Remain vigilant to protect against cherry leaf spot, apple scab and powdery mildew. Apple scab lesions were observed on some fruit in the region, and first observations of cherry leaf spot were reported. In addition, fire blight strikes in apple and pear orchards have been reported. Scout orchards to monitor for fire blight symptoms and remove disease branches as needed.

Current pests

American plum borer has been observed in the region although it was not found in traps this week. Last week, an average of 0.5 adults/trap was observed. Our tools to manage American plum borer are limited with the loss of Lorsban (chlorpyrifos). Continue to monitor borer populations. American plum borers are attracted to wounded trees, and wounds allow easy entry for borers into the tree cambium tissue. Minimize tree stress and wounding when possible. For more information about the borer pest complex and control alternatives, read the Michigan State University Extension article, “Control alternatives for borer pests of tree fruits,” by John Wise and Julianna Wilson, MSU Entomology.

Codling moth biofix is predicted to have occurred on May 14 using the Enviroweather model. For the first generation, peak egg laying is predicted to be on June 26. Only 1 codling moth/trap was found in Oceana County this week.

Dogwood borer was observed this week in Oceana County with an average of 25 borer adults/trap. Adult emergence is typically in mid-June, and egg laying occurs over a four- to six-week period. Trees with burr knots (adventitious roots) are highly susceptible to dogwood borer infestation. Burr knots typically develop on the above ground portion of the of clonal rootstocks. Dogwood borer larvae feed inside the burr knots, and if larvae continue to feed below the bark, damage can eventually girdle the tree. For more information about the borer pest complex and control alternatives, read “Control alternatives for borer pests of tree fruits."

Peach tree borer has not yet been trapped in the region. Management for borers is limited this year with the loss of Lorsban (chlorpyrifos), but mating disruption is recommended for greater and lesser peach tree borer in orchard blocks with at least 5 acres and trees that are at least 3 years old.  

Green apple aphid nymphs and adults were observed feeding on the underside of leaves this week. Growers should scout to determine if management is needed. Many aphid predators such as lady beetles and lacewings can help keep aphid populations in check. In general, established orchards can sustain thresholds of an average of three to four infested leaves on terminals before fruit damage occurs from honeydew.

Green peach aphid was observed this week. Adults and nymphs were present and caused leaf curling and yellowing from feeding on the underside of leaves. Growers should monitor orchard blocks to determine if a treatment is needed.

Lesser peach tree borer has been observed in the region. Low trap numbers were observed this week with an average of 18 borers per trap in Oceana County. Similar to greater peach tree borer, mating disruption is recommended for lesser peach tree borer in orchard blocks with at least 5 acres and trees that are at least 3 years old. 

Obliquebanded leafroller was observed in Oceana County this week. Larvae have been observed feeding on leaves, and two adults were trapped at one location. This is the second week that adults were trapped; therefore, June 13 was used to set a biofix date using the Enviroweather model for Hart. Egg hatch is predicted to begin 350 GDD after biofix, which is predicted to occur on June 25. Peak egg hatch is predicted to occur on June 27, and this will be a critical timing for management.

Oriental fruit moth biofix one is estimated to have occurred on May 9 for the first generation, and peak egg laying was predicted to occur on May 30. Moth catch has continued this week with an average of seven moths per trap.

Plum curculio adults are still active, and egg laying is occurring according to predictions of tree phenology and plum curculio developmental stage. Larvae may be observed in fruit this week.

Rose chafer adults were observed on apple on June 20. Adults typically live for three to four weeks, and females lay groups of eggs just below the surface in grassy areas of sandy, well-drained soils. Rose chafer target peach and apple. Adults feed on the fruit surface and leaf tissue. Scout sandy locations, particularly at orchard edges next to grassy areas.

San Jose scale is present in some orchards in the region. First generation crawlers were observed on June 14. Targeting the first generation crawlers will prevent mating and reproduction and will minimize the population of second generation crawlers, which typically emerge in mid-August. For infested trees, targeted sprays or oils can be used to manage scale. Growers should monitor in blocks where scale were present on fruit in 2021. San Jose scale may feed on apple, pear, plum, apricot and sweet cherry. Review summer options for controlling San Jose scale.

Spotted tentiform leafminer adults have been trapped in high numbers at the Trevor Nichols Research Center with an average of 622 adults per trap. Larvae that feed on sap of leaves may be present shortly. Treatment thresholds for early and late second-generation spotted tentiform leafminer are two to three per leaf.

Disease update

Apple scab: The RIMPro forecast is not predicting risk for apple scab this week. There is only a slight chance of rain forecasted for Saturday June 25 so conditions for spore release will not occur. Spore counts were low from the June 15-16 wetting event with four spores per rod. Although spore numbers are declining, infection can still occur. The presence of scab spores will continue to be monitored until primary scab spore release is complete. Some apple scab lesions have been observed on fruit over the past week.

Cherry leaf spot: A generally dry week also means that risk of infection by the cherry leaf spot fungus, Blumeriella jaapii, is low. Disease pressure was high in 2021 in west central Michigan and maintaining coverage of new tissue will be critical this season. Cherry leaf spot should be managed in both bearing and non-bearing orchards. Some early cherry leaf spot infections have been reported in the region.

Fire blight: Some growers have reported fire blight symptoms in apple and pear. Scout for symptoms of shoot blight and continue management with an Apogee and Actigard program. If you suspect the presence of streptomycin resistance in your orchard and would like infected tissue to be tested for resistance, please contact Emily Lavely at lavelyem@msu.edu or George Sundin at sundin@msu.edu.

Powdery mildew: Warm temperatures this week may result in powdery mildew infection. Powdery mildew causes infections on the underside of the leaf that lead to chlorotic patches or spots on the upper side of the leaf. Continue to spray for powdery mildew through midsummer.

For pest and disease management recommendations, please refer to the E-154 for product guidelines.

For more information about regional reports, please visit the Michigan State University Extension webpage.