MSU Extension Fruit & Nuts

Weather update

Mild weather is expected this week with rain forecasted every few days. Apple trees are in bloom across west central Michigan. Tart cherries and some varieties of sweet cherries are already at petal fall (Photo 1). Based on the Hart Enviroweather station for May 6, current growing degree-day (GDD) accumulation is 438 GDD₄₂ and 182 GDD₅₀. Over the past week, about 90 GDD₄₂ and 47 GDD₅₀ were accumulated.

Mild weather will continue through the week and into next week. High temperatures will be in the upper 50s and 60s with lows in the 40s this week. Rain is in the forecast from May 7 – 9 with the potential for more than 1 inch of rain in total according to the Hart Enviroweather station. Medium range forecasts call for warmer and wetter conditions over the next few weeks.

With consistent rain this spring, there is adequate moisture to support nutrient uptake. Soil temperatures are also increasing, and at a soil depth of 4 inches, the Hart Enviroweather station has recorded soil temperatures in the 60s. Soil temperatures at 2 inches range from the 60s to low 70s. With increased solar radiation, bare soil will warm more rapidly than soil covered with plant material or mulch. At soil temperatures above 45 degrees Fahrenheit, new roots are initiated, and roots become more active. Fruit trees use carbohydrate and nutrient reserves to support early season growth, but roots will also begin to take up nutrients from the soil. Nutrient application will be important over the next few weeks, particularly for nitrogen, to support early season canopy development and fruit growth according to tree age and bearing stage.

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. 

View a full weather outlook from Michigan State University meteorologist, Jeff Andresen.

Crop update

Warmer daytime and nighttime temperatures have led to rapid tree growth and flower development. Growers have been finishing up tree trimming, brush cleanup, tree planting and trellis system installation where needed. Commercial bumble bee and honey bee hives are in orchards for pollination. Many commercial and native bees are out foraging for pollen, and it is important to protect and support native and commercial bees at this time. To support bee health, avoid using capsulated insecticides during bloom which can harm bees. If an insecticide is needed, make applications at dusk or at night when bees are not active. Reduced risk insecticides should also be used, such as Sivanto or Grandevo.

Apple varieties in the west central region are in full bloom. Early varieties such as Zestar and Idared are at early petal fall. Golden delicious and empire are at full bloom. Later varieties such as Minneiska and Honeycrisp are also at full bloom. There are many fruit buds this year, and return bloom is higher than expected for many varieties considering the heavy crops in 2022 and 2023. Consider thinning fruit early, starting with blossom thinning. Thinning early can be particularly important for varieties, such as Honeycrisp, that initiate flower bud development for the following season shortly after bloom. More information on thinning strategies for Honeycrisp can be found here: Honeycrisp crop management for 2022.

For apple varieties that are shy bearing, such as SweeTango and Golden Supreme, growers can use ReTain to enhance fruit set. ReTain (AVG) is an ethylene inhibitor in fruit trees. Ethylene is a plant hormone involved in many processes such as flowering and fruit ripening. Applying ReTain at the right time during bloom will reduce ethylene levels in the flower and tree, thus delaying the aging of the flowers. This allows flowers to be receptive to pollination and fertilization for a longer period.

During bloom, flowers produce high levels of ethylene for some fruit types and varieties. Most apple varieties and sweet cherries produce high levels of ethylene during bloom. Pears produce spikes in ethylene 10 to 14 days after bloom. Ethylene can cause fruit drop during the fruit set window. Controlling the level of ethylene during flowering can help increase fruit set. More information about using ReTain can be found at:

• Using ReTain to set fruit
• ReTain application at king bloom petal fall

Tart and sweet cherry are in bloom or early petal fall. Cherry leaf spot management is important now that bract leaves have emerged. Cherry leaf spot is caused by the fungus Blumeriella jaapii. This fungus overwinters on the ground in diseased leaves. Fungal ascospores are released in spring during prolonged wetting events. In 2020, George Sundin reported that spores can infect as soon as bract leaves emerge. Spores infect through open stomata, and stomates on bract leaves were shown to be open when they emerged from buds. Bract leaves are unfolding in Oceana County, so an initial cherry leaf spot application may be needed depending on the orchard location.

Peaches are at petal fall. Venture peach trees at the West Central Michigan Research and Extension Center are at post bloom.  

Pear varieties range from late petal fall to early fruit set for varieties such as Bartlett, Gem and Cold Snap.

Plums are at petal fall and in the shuck. Apricots are at the green fruit stage.

Pest and disease update

Consider scouting reports and block history to target hot spots for early season pests in the orchard according to bud stage. Pest activity has been slow to start with the cooler weather we’ve had over the past few weeks, but with warmer temperatures, pest activity is increasing.

Apple scab

RIMPro forecast is predicting that emerging tissue in apple is at extreme risk for apple scab infection on May 13 and 14. Scab spore release is gradually increasing in Oceana County. For the rain event on May 4, only 21 spores per rod were trapped. Warmer weather means that the scab fungus, Venturia inequalis, will be more active and can infect new leaf tissue. With rapid tree growth in our region, it is important to protect new growth with adequate fungicide coverage. Coverage will also be important for pear blocks in the region for pear scab (Venturia pirina).

Powdery mildew

Warm temperatures and high humidity this week may result in powdery mildew infection. Powdery mildew is caused by the fungus Podosphaera leucotricha. It affects 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. Spray for powdery mildew from tight cluster or bloom through midsummer.

Fire blight

West central growers should continue to be vigilant and manage fire blight for blossom blight and shoot blight this year, particularly in young, high-density plantings. Fire blight risk has been low to moderate during bloom this season with EIP values below 70 (the threshold for high fire blight risk) in Oceana and Mason counties. Some higher risk conditions have been present in Newaygo County due to rain events and high temperatures during bloom.

It is still important for growers to keep blossoms protected once they open, particularly before a rain event. This is especially important for fire blight prone blocks with historically high pressure and fire blight sensitive varieties such as Ginger Gold, Fuji and Gala. Warmer temperatures this week may lead to more bacterial growth in cankers over the next few weeks and during bloom. Blossoms are expected to be at risk this weekend as trees will be in bloom, and rain showers are in the forecast.

Early season pests

On May 7, the Trevor Nichols Research Center in Fennville, Michigan, trapped the common apple pests redbanded leafroller, spotted tentiform leafminer, oriental fruit moth and codling moth. Oriental fruit moth was trapped in Fennville with an average of 68.7 moths per trap on May 6. Codling moth was trapped with an average of four moths per trap.

Plum curculio will be moving from nearby woodlots as adults to orchards as we get closer to fruit set. It is not a concern until fruit are out of the shuck or at fruit set. When young fruit are exposed, plum curculio deposit eggs under the skin of the fruit in a crescent-shaped slit. Protective sprays can be applied during the egglaying period, starting at petal fall.

For European red mite, scout for viable eggs that are bright red. If eggs are pale or clear, they are not viable. A miticide or oil may be used to manage mites at tight cluster. Hatch will begin during the pink stage and will continue through bloom. Mites have been observed in Oceana County, including twospotted spider mites.

San Jose scale is present in some orchards in the region. Targeted sprays or oils can be used for infested trees to manage scale and target adults. Males should be starting to fly in the region.

Rosy apple aphid is a common pest in our region. Scout for eggs on the bark of apple trees. For early apple varieties that may already be at pink, check for colonies in fruit clusters and treat blocks as needed.

Black stem borer first flight for females is predicted to occur after two consecutive days above 68 F. For stone fruits, this typically occurs just before or during bloom. For apples, first flight typically occurs between 0.5-inch green and pink.

Obliquebanded leafroller adults have not been trapped yet in Oceana County, but larvae have been identified. Scout problem blocks in the coming weeks to determine if a spray is needed.

Redbanded Leafroller adult fight is low in number in the region. Redbanded leafrollers and variegated leafrollers have been observed in traps in Oceana County for the past three weeks. Continue to monitor this minor tree fruit pest.

Oriental fruit moth was trapped at three locations in Oceana County with an average of 57.3 oriental fruit moths per trap. Oriental fruit moth has been trapped in Oceana County for three consecutive weeks with counts of 0.3, 8.7 and 57.3 moths per trap. For the West Central Michigan Research and Extension Center, oriental fruit moth was first observed in peaches this season, and a biofix date of April 29 has been set. They are now present in traps put in apple blocks. The biofix date can be adjusted in Enviroweather according to orchard site and site-specific trapping.

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.