MSU Extension Fruit & Nuts

Weather update

Weather has been hot and dry across the region. For the Hart weather station, high temperatures were in the 80s and lows were in the 50s and 60s over the past week. This week, temperatures are forecasted to cool slightly with highs in the low to mid-70s and lows in the 40s and 50s. Based on the Hart weather station for June 5, current growing degree day (GDD) accumulation is 861 GDD₄₂ and 499 GDD₅₀. Across the region, GDD accumulation is currently above the five-year average (Table 1). Tree phenology is advancing steadily, new shoot growth is rapid, and fruit are sizing well across west central Michigan (Figure 1).

Weather data was gathered from MSU Enviroweather.

There was scattered rain across the region on Saturday, June 3 (Table 2). For example, Hart received 0.31 inches of rain while no rain fell in New Era. Soil conditions are still very dry. For the Hart weather station on June 5, soil temperatures are 81 and 76 degrees Fahrenheit at 2 and 4 inch soil depths, respectively. Soil moisture at 4 and 20 inches deep is 1.5 and 2.1%, respectively. No significant precipitation is predicted is week. Dry and sunny conditions are forecasted for this week, and the 8-14 day outlook is expected to be moderate and drier than normal. There is some potential for brief rain showers in west Michigan on Saturday, June 10. Growers should irrigate to maintain adequate soil moisture for water and nutrient uptake, particularly for young trees.

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.

Watch the full weather outlook from MSU meteorologist Jeff Andresen.

More irrigation and irrigation scheduling information can be found below:

• Watering fruit trees with micro irrigation systems from Michigan State University Extension
• Irrigation: A critical tool for fruit quality and cropping from Michigan State University Extension
• Drip irrigation for tree fruit orchards in Pennsylvania from PennState Extension

Crop update

Weather has been beneficial for apple thinning applications. Many growers applied another thinner application over the past week. With heavy bloom and potential for a full crop this year, a standard apple thinning program should be used to enhance fruitlet size and support return bloom.

Early apple varieties in Hart have fruitlets that are 20 – 25 mm in size such as Zestar and Idared. Jonagold, Minneiska and Honeycrisp fruitlets measured 15 – 21 mm. Gala and EverCrisp fruitlets were 14 – 18 mm. As apple fruitlets continue to grow, fruit size is reaching the tail end of the window to use chemical thinners. Fruitlet size should be measured for each variety and block to target thinner applications as needed.

For more thinning recommendations, see the MSU Thinning Guide.

Specific information on thinning strategies for Honeycrisp can be found in this article Honeycrisp Crop Management for 2022.

Fruit thinning updates for New York and Michigan can be found in this video provided by Valent USA LLC. Guest speakers Amy Irish-Brown, Phil Schwallier, Dan Donahue and others discuss conditions and outlook for 2023.

Tart cherry fruitlets measured at 13 – 14 mm. Fruitlets for sweet cherry varieties ranged from 14 – 16 mm in size.

Peach fruitlets for the variety, Venture, are 18 – 20 mm in size at the West Central Michigan Research and Extension Center (WCMREC).

Pear fruitlets are 14 – 18 mm for Bartlett pear at the WCMREC.

Pest and disease update

Pests are active in the west central region. Review scouting reports and block history to target hot spots for early season pests in the orchard according to growth stage. Obliquebanded leafroller larvae and plum curculio adults have been found, but fruitlet damage has not been widely observed. Codling moth (3.3 moths/trap), lesser apple worm (1/trap) and dogwood borer (3.3/trap) were trapped this week in Oceana County.

With dry weather, some pests may thrive more this year than in previous years. For example, European red mites and twospotted spider mites do well in hot dry weather. Damaged leaves will be speckled with small yellow spots from feeding sites. Scout for European red mites and twospotted spider mites to determine if economic thresholds are met. Economic thresholds for European red mite and two-spotted spider mites are five to seven mites per leaf through July.

Summer pests

American plum borer has been observed in Oceana County. Our tools to manage American plum borer are limited with the loss of Lorsban (chlorpyrifos). Monitor borer populations and minimize tree stress and wounding as much as possible. American plum borers are attracted to wounded trees, and wounds allow easy entry for borers into the tree cambium tissue.

Codling moth biofix is predicted to have occurred on May 30 using the Enviroweather model for one location in Oceana County. Sustained trap catch has occurred, and the start of first generation egglaying was predicted for June 2. On June 11, first egg hatch is predicted. Codling moths were only found in one trap out of three in Oceana County this week.

Dogwood borer was observed this week in Oceana County. Adult emergence is typically in mid-June, and egglaying 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 clonal rootstocks. Dogwood borer larvae feed inside the burr knots. 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 John Wise and Julianna Wilson with the MSU Department of Entomology.

European red mite is active in warm and dry conditions, which are favorable for egg hatch and larvae activity. Scout for European red mites in apple and pear.

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 five acres and trees that are at least three years old.

Green apple aphid nymphs and adults were observed feeding on the underside of leaves this week. 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 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 undersides of leaves. Monitor orchard blocks to determine if a treatment is needed.

Lesser peach tree borer has been observed in Oceana County. Similar to greater peach tree borer, mating disruption is recommended for lesser peach tree borer in orchards with at least five acres and trees that are at least three years old.

Obliquebanded leafroller is predicted to have sustained catch next week. Sustained adult catch is expected at 900 GDD₄₂. Scout orchard blocks in a few weeks to determine if a spray is needed. Consider Bt sprays in problem blocks. Larvae have been found in Oceana County.

Oriental fruit moth Biofix 1 was set on May 9 for Hart. According to the Enviroweather model for oriental fruit moth, peak egglaying is predicted for June 1.

Plum curculio damage was observed this week in apples and cherries. Monitor orchards for damage, especially in areas that border wood lots.

Rosy apple aphid and woolly apple aphid are common pests in our region. Scout for colonies of rosy apple aphid nymphs in fruit clusters. Woolly apple aphids can be found at pruning scars and nodes of interior and upper branches. Treat blocks as needed.

Twospotted spider mites are active in hot and dry weather. Scout for twospotted spider mites in addition to European red mites. Check for necrosis or bronzing of leaves and webbing on the underside of the leaf.

Disease update

Disease pressure has been low so far this season, but powdery mildew has been observed in orchards across the region. Powdery mildew management is still needed in warm and dry conditions.

Apple scab: There may be some infection risk if there are rain showers this weekend. New shoot and leaf growth should be protected with adequate fungicide coverage before the next rain event. Coverage will also be important for pear blocks in the region for pear scab (Venturia pirina). In general, spore release and infection risk to date has been low this season.

Cherry leaf spot risk has been low this season. No infection events have been reported according to the Enviroweather model for Hart. Management programs target the cherry leaf spot fungus, Blumeriella jaapii. As a reminder, chlorothalonil, copper products and Captan are effective materials against cherry leaf spot. Note that chlorothalonil has a 10-day retreatment interval. New leaf tissue should be protected before the potential for rain this weekend.

Powdery mildew has been observed in apple and cherry orchards in the region. Powdery mildew is caused by the fungus Podosphaera leucotricha. Powdery mildew has been reported in other fruit growing regions in Michigan. Note that sterol inhibitors, strobilurins and succinate dehydrogenase inhibitors control powdery mildew. Captan, Scala, Vangard and EBDC fungicides will not control powdery mildew. While apple scab and cherry leaf spot pressure are currently low, growers should still spray to protect new growth from powdery mildew.

Fire blight: Shoot blight management is needed, particularly in young, high-density plantings. Target shoot blight with the current recommendation of Apogee and Actigard in combination. As a reminder – storms can bring rain, wind and hail. Monitor for hail or trauma from wind to manage fire blight infection after physical injury.

For pest and disease management recommendations, please refer to Fruit Management Guide (E-154) for product guidelines.

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