MSU Extension Fruit & Nuts

Weather update

The temperature has been cooler over the past few days with highs 70s and lows in the 50s across the region. The rest of the week will also be cooler with highs in the mid to upper 70s. Fruitlets of apple, peach, and pear continue to grow steadily while sweet and tart cherry harvest is finishing for many growers across the region (Figure 1). Based on the Hart weather station for July 26, current DD accumulation is 2085 DD₄₂ and 1335 DD₅₀ (Figure 2).

On July 23 and 24, a large storm system brought heavy rains across the region. Our region has been very dry this season overall. This latest storm system brought anywhere from 2 – 4 in of rain, and some areas are now above the 5-year average for rainfall (Table 2). Scattered thunderstorms may develop Wednesday, the 27^th. Temperatures next week are forecasted to be warmer, and potential storm systems will bring little rain. Long-range weather forecasts predict that we will have warmer and drier conditions than normal through August.

Watch the current and longer-term weather report presented by Jeff Andresen, MSU Department of Geography, Environment, and Spatial Sciences.

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

For many growers, sweet cherry harvest has finished, and tart cherry harvest is wrapping up. Many growers will finish tart cherry harvest this week. Early peach varieties are also ripening. Apples, pears, and peaches continue to grow and size well.

Apple varieties in Oceana County have average fruit diameters ranging from 55 - 70 mm. Early varieties, such as Zestar, have diameters ranging from 65 - 70 mm. Average fruit diameter for Honeycrisp was 64 mm, and for Jonagold, average fruit diameter was 60 mm. Predicted harvest dates for apple are now available from Michigan State University Extension.

Peaches are continuing to size and some early fresh varieties are ready to harvest. Average Venture peach diameter was measured at 48 mm in Oceana County.

Pear fruit diameter was measured at an average of 47 mm for Bartlett in Oceana County.

Pest and disease update

In the west central region, continue scouting blocks to target hot spots for active pests in the orchard according to growth stage. Woolly apple aphids and San Jose scale have been reported across the region. San Jose scale has been reported on fruit of apple and pear causing bright red spots. Growers are encouraged to scout to identify scale hot spots in the orchard. Some European red mites and two-spotted spider mites were observed in low numbers as well as oblique banded leafroller larvae and adults.

Oriental fruit moth was trapped in Oceana County with an average of six moths per trap. Codling moth was also trapped this week with an average of only one moth per trap.

Dogwood borer was observed at an average of 34 per trap. Lesser peach tree borer, American plum borer and peach tree borer were trapped in a tart cherry block in Oceana County, and numbers of adults have been declining. Adult obliquebanded leafrollers were also trapped this week with an average of three adults per trap. Spotted wing drosophila (SWD) were found in traps this week in Oceana County, but trap numbers remain low with fewer than 10 SWD in most locations according to local consultants. At the research station, only one female SWD was found.

Apple maggot was trapped this week with an average of one apple maggot adult per trap.

Powdery mildew has also been reported in cherry and apple, and growers should monitor blocks where disease pressure has been high in the past. With terminal bud set, powdery mildew infections should lessen. While mildew is low overall, there are still blocks that seem to have more than expected. Note these blocks for the 2023 season so mildewcides can be added in earlier for potentially high inoculum blocks.

Growers are also encouraged to manage common summer diseases in apples such as sooty block and fly speck. Consider managing apples in areas where the MSU Enviroweather model indicates adequate wetting hours for disease. The wetting hour totals vary greatly from station to station this year. For more information, check the summer disease model on Enviroweather for your local weather station.

Scab lesions were also observed in apple and pear in the region, and development of cherry leaf spot were reported on untreated trees at the West Michigan Research and Extension Center. For treated trees, cherry leaf spot development continues to be very low.

Current pests

American plum borer was trapped this week with an average of 12.5 adults per trap. Our tools to manage American plum borer are limited for fruit bearing trees with the loss of Lorsban (chlorpyrifos), but Asana is labeled for American plum borer, but no data for efficacy is available. For more information about the borer pest complex and control alternatives, read “Control alternatives for borer pests of tree fruits” by John Wise and Julianna Wilson, MSU Entomology.

Codling moth biofix is predicted to be in the second generation according to Enviroweather for Hart. Adults have been caught in two locations in Oceana County the past two weeks. Only one moth per trap was caught on July 26. Egg lay was predicted to occur on July 18, and first egg hatch was predicted for July 22.

Dogwood borer was observed this week in Oceana County with an average of 34 borer adults per trap. Adult emergence is typically in mid-June, and egg laying occurs over a four-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 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. Assail is labeled for dogwood borers in apple and should be considered if trees are infested.

Peach tree borer was observed in traps this week with an average of 4.5 borers per trap. If trees are infested, growers may consider using Asana and entomopathogenic nematodes (EPNs), which are labeled for peach tree borer management in stone fruit.

Lesser peach tree borer has been observed in the region this week with an average of 12 borers per trap in Oceana County. If trees are infested, consider using Asana and Sevin which are labeled for peach tree borer management in stone fruit. More information about the borer pest complex and control alternatives, read “Control alternatives for borer pests of tree fruits.”

Obliquebanded leafroller adults were found in traps this week with an average of three adults per trap. Larvae were also observed on leaves of apple and tart cherry trees in Oceana County this week.

Oriental fruit moth biofix 2 was predicted to have occurred on June 22 for the Hart weather station. On July 26, an average of six moths per trap were reported in Oceana County. Early egg hatch should be also underway, and cover sprays in stone fruits are critical to prevent shoot and fruit infestation. Monitor for shoot flagging – particularly non-bearing and nursery trees where oriental fruit moth can do a lot of damage.

San Jose scale is present in some orchards in the region. First generation crawlers were observed on June 14, and scale has been found on apple and pear fruit in Oceana County. Second-generation crawlers typically emerge in mid-August, this crawler stage will be another critical time for scale management in orchard hotspots. For infested trees, targeted sprays or oils can be used to manage scale until crawlers develop a waxing coating. Monitor in blocks where scale was present on fruit in 2021. San Jose scale may feed on apple, pear, plum, apricot and sweet cherry. Review summer options for controlling San Jose scale.

Spotted wing drosophila were observed in low numbers this week with one female spotted wing drosophila per trap. No males were found in traps at the West Michigan Research and Extension Center. Hot and dry weather will keep spotted wing drosophila activity low during the day, but they will be more active during cooler times of the day in the morning and evening.

Woolly apple aphid has been found throughout the region over the past few weeks. When scouting for woolly apple aphid, feel in the white fuzz to make sure aphids are still alive. The fuzz will remain even if the aphids are dead. There can be several individuals in that white fuzz. It will be important to manage woolly apple aphid so they do not because a nuisance in the canopy at harvest. Check out this video of woolly apple aphid in action and see woolly apple aphid management recommendations from MSU Extension.

Julianna Wilson from Michigan State University is looking for woolly apple aphid populations to sample from across our region. Please contact Emily Lavely at lavelyem@msu.edu if you have woolly apple aphid that could be sampled from your blocks.

Disease update

Apple scab: Primary scab is officially over for 2022. While highly unusual, primary scab spores were released later this season compared to normal years. This may be due to 1) low number of rain events that occurred this spring and 2) some rain events occurred at night when spores are not likely to be released.

Cherry leaf spot: Risk of infection by the cherry leaf spot fungus, Blumeriella jaapii, continues to be low; however, recent rain events may lead to some cherry leaf spot development. Infected leaves were observed on July 26 in untreated tart cherry trees used for a research trial with the MSU plant pathologist, George Sundin. Cherry leaf spot should be managed in both bearing and non-bearing orchards. Some cherry leaf spot infections have been reported in the region, but cherry leaf spot incidence is low so far this season.

Fire blight: Scout for symptoms of shoot blight and continue management with an Apogee and Actigard program if needed. If you suspect the presence of streptomycin resistance in your 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 some orchards in the region, shoots with blight were tested for streptomycin resistance. Presence of the fire blight pathogen, Erwinia amylovora, was confirmed, and streptomycin resistance were confirmed.

Powdery mildew: Infections of powdery mildew have been observed in tart cherry and apple orchards this week. Powdery mildew causes infections on the underside of the leaf that leads to chlorotic patches or spots on the upper side of the leaf. Continue to spray for powdery mildew through midsummer if needed. Heavy powdery mildew infection can inhibit photosynthesis and prevent leaves from producing energy. Young leaves are most susceptible to infection.

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.