MSU Extension Fruit & Nuts

Weather update 

Over the past week, temperatures have cooled slightly with highs in the low 80s and lows in the 40s, according to the Hart Enviroweather station. Temperatures will be more consistent this week with highs in the upper 70s and low 80s with lows in the 60s. Another storm moved through the region over the weekend, and 0.17 inches of rain fell on Saturday, June 29, according to the Hart Enviroweather station. Relative humidity ranged from 62 to 79% this week, and evapotranspiration has been high due to high winds. More rain is forecasted for July 2 and 3 this week.  

Fruitlets are growing steadily (Photo 1), and fruit size has been about 5 millimeters (mm) larger this year than previous years at this stage for apple, pear and peach. Based on the Hart Enviroweather station for July 1, current DD accumulation is 1,629 DD42 and 946 DD50.  

Soils continue to hold adequate moisture to support tree growth and fruitlet development. Over the past week, soil moisture ranged from 10 – 15% at 4 inches deep in the soil profile and 9 – 17% at 20 inches soil depth for the Hart Enviroweather station. Higher moisture levels are expected after the storms on July 2 and 3. Water has steadily infiltrated into the soil profile and is readily available for fine roots, which are produced in the top 1.5 – 2 feet of soil. These roots are responsible for taking up water and nutrients.  

Fertilizer applications can be made over the next few weeks. As a reminder, with the consistent and heavy rains this season and continued chances of rain in the forecast, more frequent applications of fertilizer are recommended in smaller rates compared to one or two applications in larger rates during the growing season. This is particularly important for nitrogen fertilizer as nitrogen moves readily in soil solution and can be easily leached as water moves through the soil profile. 

Soil temperatures at a depth of 2 inches have ranged from the 70s into the low 80s. High soil temperatures can inhibit root activity and cause stress. Soil temperatures at 4 inches deep have been in the 70s over the past week. Deeper in the soil profile, temperatures fluctuate less and have been in the low 70s and upper 60s at 8 and 20 inches deep. 

Weather data was gathered from 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 early apple varieties, most advanced fruitlets ranged in size from 57 – 61 mm for Zestar, and Honeycrisp fruitlets ranged from 52 – 56 mm. Minneiska fruitlets were 58 – 62 mm in Hart.  

With recent storms bringing high winds and hail, some hail damage and bruising occurred in some orchards.  

Tart and sweet cherry are continuing to grow and ripen (Photo 2). Fruit size for the sweet cherry variety Attica ranged from 26 – 27 mm. Sweet cherry varieties are being harvested, and cherries have excellent flavor. Some cracking has occurred as a result of rain before harvest, but consistency of rain this spring and high soil moisture levels may have helped prevent extensive cracking. Tart cherry fruitlets are about 20 – 22 mm in size and red. Fruit is beginning to soften, and tart cherry harvest has begun across the region. 

Consider harvest time and appropriate timing for ethephon applications for sweet and tart cherry orchards. Ethephon is a plant growth regulator that helps loosen fruit to enhance detachment of cherries during mechanical shaking by dissolving the abscission layer between the pedicel and fruit. More information from Michigan State University Extension on ethephon and application recommendations can be found here: Ethephon on cherries. 

Cherry leaf spot pressure has been high with warm and wet weather conditions. Lesions on leaves, stems and fruit have been observed across the region. Fruit lesions are not as prominent as fruit ripens and turns red. Continue protecting leaves from rapid cherry leaf spot infection. As a reminder, chlorothalonil, copper products and Captan are effective materials against cherry leaf spot. Note that chlorothalonil has a 10-day retreatment interval, and application of Captan or copper products may be needed sooner than 10 days to protect leaf and fruit tissue. Note that captan and copper application at high temperatures (80s) may lead to phytotoxicity. Apply these products at cooler temperatures or at nighttime when possible.  

Powdery mildew was observed this week in apple and cherry orchards in the region on young leaves at shoot terminals. Powdery mildew is caused by the fungus Podosphaera leucotricha. As a reminder, sterol inhibitors, strobilurins and succinate dehydrogenase inhibitors control powdery mildew. Captan, Scala, Vangard and EBDC fungicides will not control powdery mildew.  

American brown rot was observed this week in a mature sweet cherry block and in tart cherries. Cracking from rain or wounding due to high winds, hail, bird damage or bacterial canker infection in sweet cherries leads to higher likelihood of brown rot infection. As fruit gets closer to harvest, susceptibility to brown rot increases. Consider if brown rot management is needed. Using Indar may not be effective, even at the highest labeled rate of 12 ounces per acre. Previous research and resistance screening of American brown rot isolates in west central and northwest regions found that most screened fungal isolates had functional resistance to Indar. Find more information about this study. Effective materials for managing American brown rot include Merivon, Miravis and Cevya. Full coverage of all rows will be important to manage this disease.  

Peach fruitlets are growing steadily across varieties, and many growers have finished hand thinning peaches. Venture peach fruitlets are 43 – 45 mm in size at the West Central Michigan Research and Extension Center.  

Apricots are close to harvest and will be ready for harvest by the end of the week. Fruit size ranged from 53 – 55 mm. 

Pear fruitlets are growing rapidly and fruit set is moderate for varieties such as Bartlett, Gem and Cold Snap. The largest fruitlets were 34 – 38 mm in diameter for Bartlett pear trees at the West Central Michigan Research and Extension Center.  

Plums are growing rapidly with high fruit set for many varieties. Average fruitlet diameter for Stanley plum was 27 – 30 mm.  

Pest update 

Consider scouting reports and block history to target hot spots for orchard pests according to fruitlet stage. Spotted wing drosophila (SWD) was trapped this week in Oceana County at four locations. 

On July 1, the Trevor Nichols Research Center in Fennville, Michigan, trapped pests such as codling moth, adult obliquebanded leafroller, oriental fruit moth and lesser peachtree borer. These pests were also observed in Oceana County as well as dogwood borer this week. 

Codling moth counts were one moth per trap on July 1. This is first generation flight of codling moth. If moths are above economic thresholds, consider treating if mating disruption has not been used. The first generation biofix date for Oceana County was set for June 1 according to trap counts at the West Central Michigan Research and Extension Center. Other sites in Oceana and Mason counties had higher traps counts and earlier biofix dates, so trapping by orchard block or in high population areas in the orchard is critical. According to the Hart Enviroweather station, second generation adult emergence will be on July 8. 

Dogwood borer was observed this week in Oceana County at an average of 42 dogwood borer per site. Adult emergence is typically in mid-June, and egg laying 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, read this article about the borer pest complex and control alternatives by John Wise and Julianna Wilson, Michigan State University Department of Entomology. 

Greater peachtree borer (peachtree borer) has not yet been trapped in the region, but it expected soon as surrounding regions are trapping these borers. 

Lesser apple worm was observed in low numbers this week. Only 0.3 adults per trap were found in Oceana County. Lesser apple worm larvae feed on small fruit or can borer into succulent shoot terminal this time of year. Apply sprays that target adults before egg lay occurs. 

Lesser peachtree borer has been observed in the region. An average of 13.7 borers per trap were counted at the West Central Michigan Research and Extension Center. Similar to greater peachtree borer, mating disruption is recommended for lesser peachtree borer in orchard blocks with at least 5 acres and trees that are at least 3 years old.  

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 were found in pruning scars and nodes of interior and upper branches. They are starting to become more prevalent in orchards and are often denser in the center of the orchard compared to the orchard edge.  

Obliquebanded leafroller adults were trapped this week in Oceana County in tart cherry and apple orchards. An average of four adults per trap were found in apple. 

Oriental fruit moth was trapped at two locations in Oceana County with an average of 4.3 oriental fruit moths per trap. This may be the start of the second generation for some locations. Scout for oriental fruit moth evidence in peaches by looking at flagged shoots where first generation larvae burrowed into shoot terminals. Flagged terminal shoots were observed this week in peach orchards. 

Spotted wing drosophila (SWD) is now present in Oceana County with an average of 49.5 female and 17.5 male adults found per trap. SWD has been observed in other fruit grower regions across the state, and adult SWD populations are higher than normal for this time of year. With SWD now present in orchards, check for larvae in fruit to monitor fruit quality. More information and management recommendations can be found in this updated article with trapping information and updated management recommendations.  

For pest and disease management recommendations, please refer to the Michigan Fruit Management Guide (E-154) for product guidelines.      

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