MSU Extension Fruit & Nuts

Weather update

This spring has been mixed with warm and cool days. Last week, overnight temperatures on Monday and Tuesday, May 15 and 16, were at or near freezing. For the remainder of last week, highs were in the 50s and 60s and lows were in the 30s and 40s. Tree phenology is advancing steadily, and fruit are sizing well across west central Michigan (Figure 1). New shoots are also rapidly growing. Based on the Hart Enviroweather station for May 23, current growing degree day (GDD) accumulation is 535 GDD₄₂ and 277 GDD₅₀. Across the region, GDD accumulation is currently above the five-year average (Table 1).

Weather data was gathered from MSU Enviroweather.

This week, temperatures will be slightly warmer with highs in the 60s and 70s and lows in the 40s and 50s according to the Hart Enviroweather station.

Rain showers occurred on Friday, May 19, but this storm system brought little rain with only 0.12 inches and a 4-hour wetting period in Hart. Conditions were similar across the region. Dry and sunny conditions are forecasted for this week. Weather for 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. Irrigate to maintain adequate soil moisture for water and nutrient uptake, particularly for young trees. For the Hart weather station, soil moisture at 4 and 20 inches deep is 4.4 and 5.8%, 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 limited.

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

Some apple varieties have fruitlets that are already 6-8 mm in size such as Zestar, Idared and Jonagold. Later varieties such as EverCrisp are at the end of full bloom to petal fall. Hart is at 535 GDD₄₂ and 277 GDD₅₀. Trees have more blooms than expected considering the heavy crop load in 2022. With bloom over or coming to an end for most tree fruits across the region, growers are removing commercial beehives from orchards. As apple fruitlets continue to grow, fruit size is approaching 8-12 mm for many apple varieties. This size is when fruitlets are most sensitive to chemical thinner applications. 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 range from shuck split to about 8 mm. Fruitlets for early sweet cherry varieties are 12-16 mm in size.

Peach fruitlets are in the shuck or at shuck split. Venture peaches at the West Central Michigan Research and Extension Center (WCMREC) are at shuck split.

Pear varieties range from petal fall to fruit set. Bartlett pear at the WCMREC is at fruit set. Gem and Cold snap fruitlet size is about 6-8 mm.

Pest and disease update

In the west central region, pest activity is starting to rise. Consider your scouting reports and block history to target hot spots for early season pests in the orchard according to growth stage. Note that codling moth has not been trapped yet, but biofix is predicted later this week. Green fruitworm and red banded leafroller activity is slowing down, with only 1.5 and 12.3 adult per trap respectively. Obliquebanded leafroller larvae and plum curculio adults have been found, but fruitlet damage has not been observed.

New this week, American plum borers (11.7 per trap) and lesser peachtree borers (4.3 per trap) were trapped at the West Central Michigan Research and Extension Center.

Early season 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.

Black stem borer adults are active in warmer temperatures. Trapping near woodlots or injured trees is recommended to monitor for flight of females. Black stem borer was trapped last week in the west central region.

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 in late May/early June due to the cooler weather this 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 was caught again this week with a spike in moths trapped of 54 moths per trap. Biofix 1 is estimated to have occurred on May 9. Traps and lures should be placed in orchards now. Scout orchards and problem blocks. According to the Enviroweather model for oriental fruit moth, first generation eggs were laid on May 13. Peak adult emergence was predicted for May 21.

Pear psylla is commonly found in our region. Scout for adults and newly laid eggs at this stage. Early management is key to keeping damage thresholds low through the season.

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 is a common pest in our region and will be present soon. Scout for colonies of dark purple nymphs in fruit clusters and treat blocks as needed.

San Jose scale are now present in some orchards in the region. Monitor in blocks where scale were present on fruit in 2022. San Jose scale may feed on apple, pear, plum, apricot and sweet cherry. Adults will be flying and can be treated with Movento.

Disease update

Apple scab: A wetting event occurred on May 19, and some spores were released. Only 25 spores/rod were counted from a location in Oceana County. Spore numbers caught are very low compared to normal and what is predicted from the RIMPro model. This may be due to the lack of rain events or that rain showers have been light. Leaves from last year that contained spores of primary inoculum for this season may also have degraded more rapidly than in other years leading to fewer spores at the monitoring site.

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. It affects cherries, apples and pears and causes infections on the underside of the leaf that lead to chlorotic patches or spots on the upper side of the leaf. It is important to manage powdery mildew because infected blossoms can cause poor fruit set or stunted and russetted fruit. 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, you should still spray to protect new growth from powdery mildew.

Fire blight: Blossom blight pressure has been low this season. Start to manage shoot blight, particularly in young, high-density plantings. Target shoot blight with the Apogee and Actigard 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.