MSU Extension Fruit & Nuts

Weather update

The temperature has been cooler over the past few days with high temperatures in the 70s and lows in the 50s across the region. The rest of the week will be cooler with highs in the upper 70s and low 80s. Overnight temperatures have been cool with temperatures in the low 50s to low 60s. Fruitlets continue to grow steadily (Figure 1).

Based on the Hart weather station for June 27, current degree day (DD) accumulation is 1274 DD₄₂ and 755 DD₅₀ (Figure 2). Accumulation of DD has increased by about 170 DD₄₂ and about 122 DD₅₀ over the past week. Degree day accumulation is similar to the five-year average (Table 1).

Conditions are dry throughout the region. Light rain over the weekend was scattered. Soil moisture levels are low across the state. Temperatures will be cooler over the coming days compared to last week. Scattered thunderstorms may develop later today on Tuesday, June 28. A slight chance of rain is forecasted for this Thursday also, and more rain is forecasted for early next week. Growers may need to irrigate this week, especially for young or newly planted orchards and for high-density systems.

Watch the current and longer-term weather report presented by BJ Baule, MSU Department of Geography, Environment, and Spatial Sciences.

*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 finishing for many varieties. Growers can decide if hand thinning will be required for apples and peaches. Many growers are thinning peaches this week. Sweet and tart cherries are turning red, and sweet cherry harvest will begin shortly. Some growers around the state are seeing sunburn on apples and other fruit crops because of the recent sunny days with high solar radiation.

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, average apple fruitlet diameters range from 35 - 40 mm. Early varieties, such as Zestar, have diameters ranging from 40 - 45 mm. Predicted harvest dates are now available from MSU Extension.

Tart and sweet cherry fruit diameters range from 15 - 30 mm depending on the variety. Sweet and tart cherries are developing red color, and sweets are getting close to harvest. Sweet cherries have also been a target for birds in many orchards. Across the region, tart cherries have developed a red blush, and many growers are considering when to apply Ethrel before harvest.

Peach diameters range from 35 - 40 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. Other growers are thinning peaches this week.

Pear fruit diameters range from 25 - 30 mm. Fruitlets continue to size well.

Pest and disease update

In the west central region, growers should continue scouting blocks to target hot spots for active pests in the orchard according to growth stage. Green peach aphid and green apple aphid were prevalent in orchards this week. Woolly apple aphid was also observed in some locations. Oriental fruit moth and codling moth were trapped again this week. High numbers of dogwood borer (average of 79 per trap) and lesser peach tree borer (average of 21.5/trap were observed on June 27. Adult obliquebanded leafrollers were also trapped this week with an average of 16 adults/trap. Spotted wing drosophila (SWD) were found in traps this week in Oceana County.

The moderate dry weather has helped kept some diseases at bay this season. American brown rot has been observed in the region this week on sweet cherries. Growers should consider protecting trees against cherry leaf spot, apple scab, and powdery mildew where disease pressure has been high in the past. Scab lesions were observed in apple and pear in the region, and some observations of cherry leaf spot were reported. In addition, fire blight strikes in apple and pear orchards continue to be reported. Growers should 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 2 adults/trap was observed. Our tools to manage American plum borer are limited with the loss of Lorsban (chlorpyrifos). Growers should 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. Growers are encouraged to minimize tree stress and wounding when possible. For more information about the borer pest complex and control alternatives, read this article by Dr. John Wise and Dr. Julianna Wilson, MSU Entomology.

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

Dogwood borer was observed this week in Oceana County with an average of 79 borer adults/trap. Adult emergence is typically in mid-June, and egg laying occurs over a 4- to 6-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. If trees are infested with borers, growers should consider treating with Assail. For more information about the borer pest complex and control alternatives, read this article by Dr. John Wise and Dr. Julianna Wilson, MSU Entomology.

Peach tree borer was observed in traps this week with an average of 1 borer/trap. 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. For more information about the borer pest complex and control alternatives, read this article by Dr. John Wise and Dr. Julianna Wilson, MSU Entomology.

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 3-4 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. For peaches, if there are more than 5 aphid colonies/ tree, growers should consider managing these pests.

Lesser peach tree borer has been observed in the region this week with an average of 21.5 borers/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 16 adults/trap were found. Due to site variability, the biofix was adjusted to June 20 in the Enviroweather model for Hart. Egg hatch is predicted to begin 350 DD after biofix which is predicted to occur on July 3. Peak egg hatch is predicted to occur on July 4, and this will be a critical timing for management.

Oriental fruit moth biofix 1 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 was moderate this week with an average of 4 moths/trap. The Enviroweather model for Hart predicted first adult emergence on June 22. Peak adult emergence is predicted for June 29-July 3.

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 until crawlers develop a waxing coating. Growers should monitor in blocks where scale was present on fruit in 2021. San Jose scale may feed on apple, pear, plum, apricot, and sweet cherry. Click here to 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 STLM are 2-3 per leaf.

Spotted wing drosophila were observed in low numbers with week with 2-4 SWD/trap. Hot and dry weather will keep SWD activity low during the day, but they will be more active during cooler times of the day in the morning and evening. The Enviroweather model for Hart is predicting moderate SWD risk from June 21 – June 29. Expected high risk is predicted on June 29 through harvest. Growers can find more information about SWD here.

Disease update

Apple scab: There has been little risk of scab over the past week; however, there is still potential for primary scab until zero spores are released during the next rain event. Some apple scab lesions have been observed on fruit and leaves over the past week. Spores will be monitoring following rainfall later this week.

American brown rot: Brown rot was observed in some sweet cherry orchards this week. Shriveled fruit was brown, and fungal spores were seen on the fruit surface. Growers should consider if brown rot management is needed. The use of Indar may not be effective, even at the highest labeled rate of 12 oz./acre. Previous research and resistance screening of American brown rot isolates in West Central and Northwest regions found that most screened fungal isolates had functional resistance to Indar. Find more information about this study here. Effective materials for managing American brown rot include Merivon, Luna Sensation, and Flint Extra. Full coverage of all rows will be important to manage this disease.

Cherry leaf spot: A generally dry week also means that risk of infection by the cherry leaf spot (CLS) fungus, Blumeriella jaapii, is low. 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, but CLS incidence is low so far this season.

Fire blight: Some growers have reported fire blight symptoms in apple and pear this week. Growers are encouraged to scout for symptoms of shoot blight and continue management with an Apogee and Actigard program. If growers suspect the presence of streptomycin resistance in their 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. Growers should 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.