MSU Extension Fruit & Nuts

Weather update

This week, temperatures will peak on June 14 and 15 as highs reach the upper 80s. A slight cool down will occur later in the week with highs in the low 70s. Humidity will remain high throughout the region. Fruitlets continue to grow steadily (Figure 1), and growers are evaluating additional needs for thinning in apple as well as peaches.

Based on the Hart weather station for June 13, current DD accumulation is 927 DD₄₂ and 529 DD₅₀ (Figure 2). Accumulation of DD has increased by about 120 DD₄₂ and about 65 DD₅₀ over the past week. Degree day accumulation is similar to 5-yr average (Table 1).

Storms brought rain in some areas across the region on June 11 and 14 (Table 2). Temperatures are predicted to be cooler than normal for the remainder of the month of June according to Jeff Andresen, Michigan State University. Watch Andresen’s current weather report.

*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 size, and warmer weather has increased pest activity across the region.  Effects of thinning applications can be evaluated this week. With warmer temperatures, the effects of June drop and thinner applications should be more evident. Growers can decide if a final thinning spray is needed or if hand thinning will be required for apples and peaches.

Apple varieties in the west central region are being monitored, and fruitlet diameter increased by 2-4 mm over the past 4 days for many varieties. In Oceana County, fruitlet diameters range from 20 - 25 mm for Gala, 25 - 30 mm for Honeycrisp, 20 - 23 for Empire, and 24 - 27 for Jonagold. Growers are advised to consider if another thinner application will be needed. For Hart, MI, the NEWA Cornell Apple Carbohydrate Thinning Model is predicting a carbon surplus for June 15, and the model recommends a 30% increase in chemical thinning rate with the addition of oil as a surfactant. Orchard blocks may not need additional thinner applications, so it is important for growers to determine the need for thinners for each block and variety.

For more thinning recommendations, growers can access the 2022 Thinning Guide.

For specific information on thinning strategies for Honeycrisp in 2022, check out this article from MSU Extension specialist, Anna Wallis, Honeycrisp Crop Management for 2022.

Tart and sweet cherry fruit diameters range from 12 - 16 mm. Some sweet cherries are developing red color.

Peach fruitlets are sizing well. Fruit diameters range from 20 - 24 mm. Growers should evaluate if thinning will be needed.

Pear fruit diameters range from 18 - 20 mm. Fruitlets are sizing well, and clusters are thinning down to 1 or 2 fruit per cluster.

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. 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 14. Low trap numbers were observed for oriental fruit moth and codling moth on June 13. An adult obliquebanded leafroller was also trapped this week.

Growers should remain vigilant to protect against cherry leaf spot, apple scab, and powdery mildew given the rain and warmer temperatures this week. A couple orchards have reported fire blight strikes in apple and pear. Growers should scout orchards to monitor for fire blight symptoms.

Current pests

American plum borer has been observed in the region. This 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). 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. Sustained trap catch has occurred, and the start of 1^st generation egg laying was predicted for May 26. On June 15, 20% egg hatch is predicted. Codling moths were not found in traps in Oceana County this week.

Dogwood borer was observed this week in Oceana County. 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. For more information about the borer pest complex and control alternatives, read this article by Dr. John Wise and Dr. Julianna Wilson, MSU Entomology.

European red mite adults and eggs were observed in low numbers at the end of last week. Warm and dry conditions are favorable for larvae activity so more activity may be observed this week. The recommended treatment threshold for European red mites is 5-7 mites per leaf through July. Mite predators were also observed this week which will help keep mite populations in check.

Greater peach tree borer (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 orchards 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 predicators 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 undersides of leaves. Growers should monitor orchard blocks to determine if a treatment is needed.

Lesser apple worm was observed in low numbers this week. Two adults were found in a trap at an orchard in Oceana County. Lesser apple worm larvae feed on small fruit or can borer into succulent shoot terminal this time of year. Growers should apply sprays that target adults before egg lay occurs.

Lesser peach tree borer has been observed in the region. Low trap numbers were observed this week with an average of 1 borer/trap in Oceana County. Similar to greater peach tree borer, mating disruption is recommended for lesser peach tree borer in orchards with at least 5 acres and trees that are at least 3 years old. 

Obliquebanded leafroller was observed in Oceana County this week. Caterpillars have been observed feeding on leaves, and 1 adult was trapped this week. A biofix date has not yet been set. Growers should continue to scout orchard blocks in the coming week to determine if a spray is needed.

Oriental fruit moth biofix 1 is estimated to have occurred on May 9. Sustained trap catch has occurred, and first egg lay occurred on May 11. Peak egg laying was predicted for May 30. Moth catch has been observed again this week in low numbers.

Plum curculio adults are still active, and egg lay is occurring according to predictions of tree phenology and PC developmental stage. Larvae may be observed this week. Growers should continue to monitor their orchards for damage, especially in areas that border wood lots to determine if a spray is needed.

Rose chafer adults were observed on apple on June 14. Adults typically live for 3-4 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. Growers should scout sandy locations, particularly at orchard edges next to grassy areas.

Rosy apple aphid is a common pest in our region. Growers can scout for colonies of dark purple nymphs in fruit clusters and treat blocks as needed.

San Jose scale is present in some orchards in the region. An average of 4 San Jose scale were trapped at the Trevor Nichols Research Center this week. First generation crawlers typically emerge mid- to late June. Targeting the first-generation crawlers will prevent mating and reproduction. Managing the first-generation crawlers 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. 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 408 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.

Disease update

Apple scab: RIMPro forecast is predicting a slight infection risk for apple scab on June 16 and 19 (Figure 3). Wettings events are predicted for June 16 and 18-19 this week. Spore counts are low but are still present. Due to heavy rains occurring during the afternoon, spores were released in higher numbers on June 13. Spore counts were 24 spores/rod. Although spore numbers are declining, infection can still occur. Primary scab spores continue to be released.

Powdery mildew: Warm temperatures and high humidity to come 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.

Cherry leaf spot: Wetting events this week may lead to infection periods for the cherry leaf spot fungus, Blumeriella jaapii. Disease pressure was high in 2021 in West Central, and maintaining coverage of new tissue will be critical this season. Cherry leaf spot should be managed in both bearing and non-bearing orchards. No evidence of cherry leaf spot infection has been found yet from previous infection periods.

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.

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.