MSU Extension Fruit & Nuts

Weather update

Warm weather is here this week, and fruit trees are in bloom across west central Michigan (Photo 1). Based on the Hart Enviroweather station for May 8, current growing degree day (GDD) accumulation is 332 GDD₄₂ and 161 GDD₅₀ (Table 1). Over the past week, about 80 GDD₄₂ and 40 GDD₅₀ were accumulated.

Warm weather will continue through the week with a slight cool down beginning next week. Highs will be in the 60s and 70s with lows in the 40s and 50s this week. This week will be generally dry this week with forecasted rain showers Friday evening (May 12). Medium range forecasts call for cooler than normal temperatures and precipitation below normal over the next few weeks.

There has been little rain in the region over the past week. Soil has dried out in the field, but there is adequate moisture to support nutrient uptake. Soil temperatures are also increasing. At soil depth of 4 inches, the Hart Enviroweather station has recorded soil temperatures with a range between the 40s and low 60s. 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. Growers are encouraged to apply nutrients over the next few weeks, particularly 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.

Watch the full weather outlook from MSU meteorologist Jeff Andresen.

Crop update

Warmer daytime and nighttime temperatures have led to rapid tree growth and flower development. Growers in the region have been finishing up tree trimming, brush cleanup, tree planting and trellis system installation where needed. Commercial bumble bee and hone ybee hives are in orchards for pollination (Photo 3). Many bees are out foraging for pollen. Consider how to protect and support native and commercial bees. 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. You can also use reduced risk insecticides such as Sivanto or Grandevo.

Apple varieties in the west central region range from pink to bloom. Early varieties such as Zestar and Idared are in bloom. Gold Delicious and Empire are at king bloom. Later varieties such as Minneiska and Honeycrisp are at pink. There are many fruit buds this year, and return bloom is higher than expected in 2023 considering a heavy crop last year. 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 in the Michigan State University Extension article, “Honeycrisp crop management for 2022.”

For apple varieties that are shy bearing, such as SweeTango and Golden Supreme, 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 cherry 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 below.

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

Tart and sweet cherry are in bloom. Upcoming weather is forecasted to be warm and dry over the next week which will support bee activity and pollination.

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

Pear varieties range from first white to bloom for varieties such as Bartlett, Gem and Cold Snap.

Plums are at bloom to petal fall. Apricots are at petal fall to fruit set.

Pest and disease update

In the west central region, greater insect activity is expected this week due to the warmer weather. Consider your 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.

Early season pests

On May 8, the Trevor Nichols Research Center in Fennville, Michigan, trapped the common apple pests red banded leafroller, spotted tentiform leafminer and oriental fruit moth. Oriental fruit moth was trapped for the first time in Fennville (average of 63 per trap) on May 8 and was also trapped in Oceana County for the first time with 1.5 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 egg laying 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.

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.

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. 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. Continue to monitor this minor tree fruit pest.

Oriental fruit moth was trapped at one location in Oceana County on May 8. Only 1.5 oriental fruit moths per trap were counted. According to the Enviroweather model, May 8 is set as the biofix, and first egg lay is predicted to be on May 13. The biofix date can be adjusted in Enviroweather according to orchard site and site-specific trapping.

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 still low in Oceana County. For the rain event on May 6, only six spores per rod were trapped. Upcoming warmer weather means that the scab fungus, Venturia inequalis, will be more active and can infect leaf tissue quickly. 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.

Cherry leaf spot: Tart cherry growers should consider starting cherry leaf spot management once 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, MSU’s 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.

Fire blight: West central growers should continue to be vigilant and manage fire blight as blossom blight and shoot blight this year, particularly in young, high-density plantings. Warmer temperatures this week may lead to more bacterial growth in cankers over the next few weeks and during bloom so it will be important for growers to keep blossoms protected once they open. Blossoms are expected to be at risk this weekend as trees will be in bloom, and rain showers are in the forecast.

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.