MSU Extension Fruit & Nuts

Weather update 

This week began with high hot and dry conditions across the west central and Grand Rapids, Michigan, regions. Fruitlets are growing steadily, and cherries are turning red. Tart cherry, sweet cherry, peach, pear and apple are sizing well (Figure 1), and June drop was observed in apples and peaches. 

For the start of the week, highs in the west central region were in the mid- to upper 80s. Highs in the Grand Rapids region were in the low 90s. Nighttime temperature stayed hot across the regions with lows in the 70s according to the Hart and Sparta Enviroweather stations.  

This week will bring a storm system on Wednesday or Thursday with slightly cooler temperatures and chances of rain the rest of the week. Based on the Hart Enviroweather station for June 23, current degree day (DD) accumulation is 1,226 DD42 and 701 DD50. For the Sparta Enviroweather station, current DD accumulation is 1,423 DD42 and 850 DD50. Growing degree days jumped from last week due to the heat. Across the regions, growing degree days are still behind the five-year average. Over the next week, forecasts call for near normal to above normal temperatures and seasonal precipitation. 

Get the full weather update from Jeff Andresen  

Current degree day accumulation is lower than the five-year average for the west central (Table 1) and Grand Rapids (Table 2) regions, according to the Enviroweather stations.  

Table 1. West Central Region: Current and 5-year average DD summary from Jan. 1- June 23. Numerical integration was used for degree day calculations. 

Table 2. Grand Rapids Region: Current and 5-year average DD summary from Jan. 1- June 23. Numerical integration was used for degree day calculations. 

Weather data was gathered from Enviroweather.  

Over the past week, much needed rain fell across the regions. In Hart, 0.55 inches of rain fell from June 18-21. In Sparta, 0.50 inches of rain fell from June 18-20. This week, storms are forecasted to bring about a half-inch of rain, which will help replenish soil moisture. Soil conditions continue to be very dry, especially for the west central region. With high temperatures and low soil moisture content, trees may easily become water stressed and will need irrigation this week.  

For the Hart Enviroweather station on June 23, maximum soil temperature was 86.7 degrees Fahrenheit at 2 inches and 82.2 F at 4 inches. This is a market increase in temperature from last week by almost 10 degrees. Maximum soil moisture on June 23 is 4.2% at 4 inches and 4.8% at 20 inches. Soil moisture has been gradually declining, even with short periods of rainfall. There has not been enough consistent rain to replenish soil moisture levels.  

For the Sparta Enviroweather station on June 23, maximum soil temperature was 96.5 F at 2 inches and 90.7 F at 4 inches. Maximum soil moisture is 49.4% at 0-12 inches and 56.3% at 12-24 inches, similar to last week. Soil with higher silt and clay content, such as in the Grand Rapids region, has the ability to hold higher levels of soil moisture compared to sandy soils (water holding capacity); however, these soils also hold water more tightly which means as the soil moisture levels go down, water is tightly held in soil pores, and it is harder for plants to access this water.  

There is evidence that increasing soil organic matter can help create and stabilize soil structure, which can also help increase water storage in soil. Irrigation is needed in both regions, particularly for young trees.  

Ground cover and higher soil moisture content from rain or irrigation help keep soils cooler which could enhance root and soil microbial activity in the soil. There are high evaporation rates right now across Michigan primarily because of solar radiation and windy conditions.  

Information and recommendations for irrigation can be found at:  

• Watering fruit trees with micro-irrigation systems - MSU Extension 
• Apple Irrigation Model | NEWA  
• Drip Irrigation for Tree Fruit Orchards in Pennsylvania  

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 

Apple varieties in Oceana County are sizing well, especially with the heat over the past few days. Fruit size for early varieties is about 38-48 millimeters (mm). In Hart, Zestar have an average fruitlet size of 43.5 mm, and Idared have an average fruit size of 39.5 mm. Honeycrisp have an average size of 36.9 mm, and Gala averaged about 29 mm. June drop is occurring, and results of chemical thinner applications are becoming more apparent. Some growers are beginning to hand thin. 

Sweet cherry are growing steadily and turning red. Harvest of early varieties of sweet cherry may begin this week. Average fruit size is 26 mm for sweet cherry. Average fruitlet size for tart cherry was 18 mm. Tart cherries are beginning to turn red in Oceana County. Tart cherry in Mason County are primarily straw colored with slight red starting to show. Heat is rapidly advancing fruit development.  

Peaches are differentiating by size. Fruit that is persisting is about 29 mm in diameter for Venture peach at the West Central Michigan Research and Extension Center. Growers are starting to hand thin peaches in the region. A general rule of thumb is to leave an average of 6 to 8 inches between fruit (the larger spacing for earlier or hard-to-size varieties). Two or three peaches can be left clustered if there is enough additional limb space and leaves to support their growth. Remove small fruit and leave larger fruit, even if they are clustered. 

Apricots are growing steadily. Average fruit size is 39 mm in Oceana County. Hand thinning of apricots can be done as needed to improve fruit size and sugar content of remaining fruit. 

Plums have a good set for European and Japanese varieties. Stanley plums measured 20 mm on average. June drop is occurring in plum. There was heavy set for some varieties. Some bacterial spot was also observed on plum leaves resulting in a shothole appearance where dead tissue fell out of leaves.  

Pear fruitlets are growing. Average fruitlet size was 27 mm for Bartlett pear at the West Central Michigan Research and Extension Center. Some pear scab was observed in the region, and damage from freeze injury is showing up as scaring on the fruit surface.  

Pest and disease update 

Diseases 

There will be risk for apple scab and cherry leaf spot this week with the chances for rain. Primary apple scab spores are still being monitored in the Grand Rapids area and in New Era. From the rainfall last Friday, one apple scab spore was trapped in New Era. No infection was recorded according to the Enviroweather apple scab model for New Era or Sparta as the period of rainfall was short. The Enviroweather model is predicting 100% of spores are mature and 99% of spores have been released in Hart and 100% of spores have been released in Sparta. These predictions are also similar to RIMPro predictions for both regions.  

Managing summer diseases such as fly speck and sooty blotch is important going forward. A scheduled fungicide program from mid-June through August will be effective against these diseases.  

Insect pests 

In Oceana County, no green fruitworm or redbanded leafroller were caught this week. Oriental fruit moth was trapped with an average of seven moths per trap.  

American plum borer was not trapped this week at the West Central Michigan Research and Extension Center, but one borer per trap was found in Mason County. Lesser peachtree borer was trapped in Oceana and Mason counties with an average of 1.6 borers per trap at the West Central Michigan Research and Extension Center and two borers per trap in Mason County. Dogwood borer was trapped at one location in Oceana County with three borers per trap. 

Codling moth was trapped in Oceana and Mason counties with an average of 0.5 moths per trap in Oceana and three per trap in Mason. No lesser apple worms were trapped. Two obliquebanded leafrollers were also trapped this week in Oceana with the MSU trapline. 

Spotted wind drosophila is being trapped in Oceana and Mason counties. Adult flies were trapped for the first time last week. Now that fruit are turning red, they are becoming susceptible to spotted wing drosophila. According to the MSU Enviroweather model for spotted wing drosophila, fruit coloring occurs at 954 to 1170 growing degree days after bloom (at base 39.2 F). During this period, there is medium risk predicted. High risk of infestation is predicted once fruit are ripe.  

For example, if bloom time was May 10, high infestation risk is predicted to begin June 29. Higher temperatures also advance pest development and generation time; however, high temperatures in the 90s may slow insect development.  

Focus on managing adults with excellent coverage, full covers and tightening spray intervals if populations build. A minimum of seven-day spray intervals under dry conditions is recommended with tighter intervals following a rain or other wetting event if needed. Be sure to rotate chemistries to manage for resistance of spotted wing drosophila. Trap counts are not necessarily an indicator of fruit infestation. It is important to sample fruit to monitor if larvae are present in fruit. Read more information about spotted wing drosophila management.  

In Sparta, codling moth was trapped at 22 moths per trap. Four oriental fruit moth were trapped, which may mark the start of the second generation of oriental fruit moth. Obliquebanded leafroller adults were also observed this week with 109 moths per trap. Dogwood borer adults have not been trapped. 

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.  

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.  

Green peach aphid may be present in orchards this week. Adults and nymphs cause leaf curling and yellowing from feeding on the undersides of leaves. Monitor orchard blocks to determine if treatment is needed.  

Scout for rose chafer adults on leaves and fruit where rose chafer typically feed. Damage can be more severe in sandy locations near the orchard edge and grassy areas.  

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 have been observed in orchards this week. 

Twospotted spider mites are active in hot and dry weather like have right now. Scout for two spotted spider mites in addition to European red mites. Check for necrosis or bronzing of leaves and webbing on the underside of the leaf. Twospotted spider mites can impact leaf health in combination with European red mite and plum rust mite if feeding is heavy. “Firing” in tart cherry has been associated with this mite complex and can cause branch die back in hot and dry conditions.  

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