West central Michigan tree fruit update – June 20, 2023

Emily Lavely<lavelyem@msu.edu>, Michigan State University Extension - June 20, 2023

Tart cherries are starting to turn red, and sweet cherry harvest is around the corner. Growers are hand thinning peaches and apples to maximize fruit size this season.

Stage of tree phenology for tart cherry, sweet cherry, peach, apricot, apple, and pear. — Photo 1. Stage of tree phenology for tart cherry, sweet cherry, peach, apricot, apple, and pear in Oceana County on June 19, 2023. Photo by Emily Lavely, MSU Extension.

Weather update

Weather has been warm and largely dry across the region over the past week. Scattered showers did bring some much-needed rain on Tuesday, June 13, and rain/mist in some locations on Thursday, June 15. Over the past week, high temperatures have ranged from the upper 60s to mid-80s. Low temperatures have ranged from the 40s to the upper 50s. This week, temperatures are forecasted to be hot. Highs will be in the 80s through the rest of the week. Based on the Hart weather station for June 19, current growing degree day (GDD) accumulation is 1,097 GDD₄₂ and 633 GDD₅₀. For many sites across the region, GDD accumulation is currently above the five-year average (Table 1). Fruitlets and new shoots continue to grow rapidly across west central Michigan. June drop is almost done across crops.

Table 1. Current and five-year average GDD summary from March 1 – June 20. Numerical integration was used for degree day calculations.
Station	2023 GDD Base 42 F	5-yr Avg GDD Base 42 F	2023 GDD Base 50 F	5-yr Avg GDD Base 50 F
Benona / Shelby	1062	1008	603	566
Elbridge / Hart	1104	1099	652	641
Fremont	1211	1183	734	701
Grant	1186	1189	712	703
Hart	1086	1080	626	623
Ludington	1018	1038	576	592
Mears	1062	1132	608	659
New Era	1151	1088	678	614

Weather data was gathered from MSU Enviroweather

There were light rain showers across the region on Tuesday, June 13, and Thursday, June 15. The Hart Enviroweather station reported 0.32 inches of rainfall on June 13. Soil conditions are still very dry. For the Hart weather station on June 19, soil temperatures are high at 80 and 76 degrees Fahrenheit at 2- and 4-inch soil depths, respectively. Scattered rainfall was not heavy enough to replenish soil moisture. Soil moisture at 4 and 20 inches deep is 1.7% and 0.9%, respectively. Chances of rain are predicted next week although no significant accumulation is predicted. The 8-14 day outlook is expected to be moderate and drier than normal. Growers should continue to irrigate to maintain adequate soil moisture for water and nutrient uptake, particularly for young trees.

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.

Crop update

Early apple varieties in Hart have fruitlets that are 40 – 43 mm in size for Zestar and 32 – 35 mm for Idared. Minneiska and Honeycrisp fruitlets measured average fruit size is 35 mm. Empire ranged from 28 – 32 mm, and Gala fruitlets ranged from 24 – 28 mm. As apple fruitlets continue to grow, fruit size is reaching the tail end of the window to use chemical thinners for later varieties. Some growers are beginning to hand thin varieties that set heavier than expected, such as Gala.

Tart cherry fruitlets measured at 15 –19 mm. Fruitlets for sweet cherry varieties ranged from 25 - 28 mm in size. Cracking has been observed on sweet cherries from rain events last week. Some products such as Parka and Rainguard can be applied to help minimize cracking and help strengthen the fruit cuticle. More information about cherry cracking and mitigation strategies can be found from an Oregon State University bulletin.

Peach fruitlet size for the variety, Venture, ranged from 28 – 32 mm in size at the West Central Michigan Research and Extension Center (WCMREC).

Pear fruitlet size ranged from 22 – 25 mm for Bartlett pear at the WCMREC.

Pest and disease update

Summer pests

American plum borer counts were zero per trap as of last week.

Codling moth counts were zero this week. Traps will be monitored to set the biofix for the second generation, which will likely be in July.

Dogwood borer was observed this week at the WCMREC with two borers per trap.

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 peach tree borer (peach tree borer) was trapped for the first time at the WCMREC with one borer per trap.

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 from honeydew.

Green peach aphid was observed this week. Adults and nymphs were present and caused leaf curling and yellowing from feeding on the undersides of leaves. Monitor orchard blocks to determine if a treatment is needed.

Lesser peach tree borer counts were down this week with only 0.3 borers per trap on average.

Obliquebanded leafroller was trapped this week for the first time. One adult was trapped at the WCMREC. A biofix date will be set after sustained catch.

Oriental fruit moth was not found in traps this week at two locations in Oceana County.

Rose chafer was observed for the first time this week in sweet cherry and peach. Adults feed on leaves and fruit. 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. Scout for twospotted 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.

Disease update

Disease pressure is low this season, but powdery mildew has been observed in orchards across the region. Powdery mildew management is still needed in warm and dry conditions. The rain event on June 13 resulted in scab and cherry leaf spot infection periods. Upcoming rain events next week will likely result in further infection periods.

Apple scab: There was a scab infection period during the rain event on Tuesday, June 13. Spores were released and 229 spores per rod were found which is the highest release this season. There was some rain/mist on Thursday, June 15, and only 10 spores per rod were trapped on that date. Spore maturity is at 100%, and we are waiting for more rain and the final release of spores this season.

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). As a general rule of thumb, fungicides should be reapplied after 2 inches of rain or if rain is very heavy.

Cherry leaf spot risk has been low this season, and the second infection event for Hart was reported on June 13 according to the Enviroweather model. New leaf tissue should be protected before the potential rain this weekend.

Powdery mildew has been observed in apple and cherry orchards in the region. While apple scab and cherry leaf spot pressure are currently low, growers need to protect new growth from powdery mildew.

Nectria twig blight has been observed in some apple orchards this season (Photo 2). Blighting shoots may resemble fire blight infections, but infected shoots wilt from the base of the canker upwards rather than the from the shoot tip downwards as seen with fire blight. Cornell University has more information about nectria twig blight management and how to distinguish it from fire blight.

Nectria Twig Blight on apple leaf. — Photo 2. Nectria twig blight in Gala observed on June 12, 2023. Photo by Emily Lavely, MSU Extension.

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.

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