MSU Extension Fruit & Nuts

Weather update

The weather has been cooler and largely dry across the region. Scattered showers did bring some much-needed rain on Sunday, June 12. Over the past week, high temperatures have ranged from the upper 50s to upper 70s. Low temperatures have ranged from the upper 30s to the low 50s. This week, temperatures are forecasted to gradually increase. The week will start with highs in the low 60s, and highs will be in the 70s through the rest of the week. Based on the Hart weather station for June 12, current growing degree day (GDD) accumulation is 976 GDD₄₂ and 565 GDD₅₀. For many sites across the region, GDD accumulation is currently above the five-year average (Table 1). Fruitlets and new shoots continue to grow rapidly across west central Michigan (Photo 1).

Weather data was gathered from MSU Enviroweather.

There were light rain showers across the region on Sunday, June 11 (Table 2). Soil conditions are still very dry. For the Hart weather station on June 12, soil temperatures are about 5 degrees cooler than the previous week and are 76 and 71 degrees Fahrenheit at 2- and 4-inch soil depths, respectively. Even though it rained on Saturday, rainfall was not heavy enough to replenish soil moisture. Soil moisture at 4 and 20 inches deep is 1.2 and 1%, respectively.

More precipitation is predicted this week on Tuesday (June 13), Thursday and Saturday, although no significant accumulation is predicted. The 8-14 day outlook is expected to be moderate and drier than normal. 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

Many growers have finished thinning apples for this year. As June drop is occurring, fruit set for apple, cherry, peach and pear is becoming more evident for this season.

Early apple varieties in Hart have fruitlets that are 35 – 40 mm in size such as Zestar and Idared. Jonagold, Minneiska and Honeycrisp fruitlets measured 25 – 30 mm. Gala and EverCrisp fruitlets were 18 – 24 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 14 – 16 mm. Fruitlets for sweet cherry varieties ranged from 18 – 22 mm in size.

Peach fruitlets for early fresh varieties ranged in size from 26 – 28 mm. Venture peach fruitlet sized ranged from 24 – 26 mm in size at the West Central Michigan Research and Extension Center (WCMREC).

Pear fruitlets are 18 – 23 mm for Bartlett pear at the WCMREC.

Pest and disease update

In the west central region, trap counts for adult obliquebanded leafroller, redbanded leafroller and codling moth were zero. Low numbers of oriental fruit moth (0.7 moths/trap), lesser apple worm (0.3/trap) and dogwood borer (4.3/trap) were trapped this week in Oceana County. Obliquebanded leafroller larvae and plum curculio adults have been found, but fruitlet damage has not been widely observed. Aphids have also been observed in apples, peaches and cherries.

With dry weather, some pests may thrive more this year than in previous years. For example, 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 twospotted 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 egg laying 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, 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 Michigan State University Extension article, “Control alternatives for borer pests of tree fruits,” by John Wise and Julianna Wilson with the Department of Entomology at MSU.

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 apples and pears.

Greater peachtree borer (peachtree 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 peachtree 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 peachtree borer has been observed in Oceana County. Similar to greater peachtree borer, mating disruption is recommended for lesser peachtree 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.

Plum curculio damage was observed this week in apples and cherries. Growers should 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. The rain event on June 11 resulted in scab and cherry leaf spot infection periods. Upcoming rain events this week will likely result in further infection periods.

Apple scab: There was a scab infection period during the rain event on Sunday, June 11. Spores were released and 22.5 spores/rod were found. Spores release has been low during rain events this season. It is likely that the hot dry weather has caused some spores to dry out. Since spores are still being released, primary scab season is continuing. Spore maturity is at 100%.

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). As a general rule of thumb, fungicides should be reapplied after 2 inches of rain or if rain is very heavy.

Cherry leaf spot: Cherry leaf spot risk has been low this season, and the first infection event for Hart was reported on June 11 according to the Enviroweather model. 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: 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.