MSU Extension Fruit & Nuts

Weather update

Weather continues to be hot and dry across the region. For the Hart weather station, temperatures warmed up leading to Memorial Day with highs in the upper 70s and lower 80s. This week, high temperatures will be in the low 80s with low temperatures in the upper 50s and low 60s. Based on the Hart weather station for May 29, current growing degree day (GDD) accumulation is 656 GDD₄₂ and 350 GDD₅₀. Across the region, GDD accumulation is currently above the five-year average (Table 1). Tree phenology is advancing steadily, and fruit are sizing well across west central Michigan (Figure 1).

Weather data was gathered from MSU Enviroweather.

There is some potential for popup rain showers in west Michigan, but the chance of rain is low. No significant precipitation is predicted this 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.

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.

Soil moisture is very low, and little rain is forecasted over the coming weeks. Growers should irrigate to maintain adequate soil moisture for water and nutrient uptake, particularly for young trees. For the Hart weather station, soil temperatures are 76 and 71 degrees Fahrenheit at 2- and 4-inch soil depths, respectively. Soil moisture at 4 and 20 inches deep is 1.9% and 4% respectively. Dry soils can limit nutrient availability to plants, particularly nutrients that move readily through water (mass flow) such as nitrogen, sulfur, calcium and magnesium.

Phosphorus and potassium move through the soil solution and to the root surface by diffusion in response to a concentration gradient. As roots take up nutrients, the nutrient concentration around the root is low. The nutrient concentration in soil solution away from the root is higher than around the root, so nutrients move from high to low concentration until an equilibrium is reached. However, if soils are dry, nutrient movement through diffusion is also limited.

Irrigation is recommended where possible, particularly for young fruit trees.

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

The weather has been beneficial for apple thinning applications. Many growers applied thinners last Friday and Saturday for the 8 – 12 mm fruitlet timing. With heavy bloom and potential for a full crop this year, a standard apple thinning program should be used.

Early apple varieties near Hart have fruitlets that are already 15 – 20 mm in size such as Zestar and Idared. Jonagold, Minneiska and Honeycrisp fruitlets measured 10 – 15 mm. Gala and EverCrisp fruitlets were 6 – 10 mm. As apple fruitlets continue to grow, fruit size is in the appropriate window to use chemical thinners. Fruitlet size should be measured for each variety and block to target thinner applications as needed.

Monitor temperatures this week, and be cautious if temperatures approach 85 F. If temperatures are over 85 F, do not apply a thinner.

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 10 – 12 mm. Fruitlets for early sweet cherry varieties are 15 – 18 mm in size.

Peach fruitlets for the variety Venture are 8 – 10 mm in size at the West Central Michigan Research and Extension Center (WCMREC).

Pear fruitlets are 6 – 8mm for Bartlett pear at the WCMREC.

Pest and disease update

In the west central region, pest activity is starting to rise. 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 observed. Codling moth was reported in traps last week in Oceana County.

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.

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 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 peach tree borer in orchards with at least five acres and trees that are at least three years old.

Lesser peachtree borer has been observed in Oceana County. Similar to greater peachtree 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 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.

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: This week, no infection risk is expected due to moderate temperatures and dry conditions. However, 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, and 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.

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.

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.