MSU Extension Fruit & Nuts

Weather update 

Temperatures over the past week have continued to be mild with highs in the 50s up to the low 70s and lows ranging from the upper 30s to the mid-50s according to the Hart Enviroweather station. Storms brought over 0.5 inches of rain across the region as well since May 8, and relative humidity has consistently been over 60%.  

Similar temperatures are forecasted for this upcoming week with intermittent chances of rain between 30 – 60% on Tuesday and Thursday, May 14 and 16. Stone fruit are at shuck split (Figure 1), and apple and pear are at fruit set with some lingering bloom. Based on the Hart weather station for May 13, current growing degree-day (GDD) accumulation is 535 GDD42 and 230 GDD50. Over the past week, about 82 GDD42 and 41 GDD50 were accumulated.  

Medium range forecasts call for warmer and near normal or above normal precipitation over the next few weeks. 

With rain over the past week, soil moisture has ranged from 18-12% at 4 inches deep in the soil profile and about 10% at 20 inches soil depth for the Hart Enviroweather station. Soil temperatures at a depth of 2 inches have ranged from the low 60s to low 70s. Soil temperatures at 4 inches deep have been in the 60s over the past week. With increased solar radiation, bare soil will warm more rapidly than soil covered with plant material or mulch. Soils with adequate moisture provide nutrients to plants, particularly nutrients that move readily through water (mass flow) such as nitrogen, sulfur, calcium and magnesium.  

Phosphorus and potassium move through the soil solution and to the root surface by diffusion in response to a concentration gradient. As roots take up nutrients, the nutrient concentration around the root is low. The nutrient concentration in soil solution away from the root is higher than around the root, so nutrients move from high to low concentration until an equilibrium is reached. Adequate soil moisture supports diffusion of these important nutrients; however, if soils are dry, nutrient movement through diffusion is limited.  

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 

With moderate temperatures, tree growth and fruitlet development has been steady. Tree trimming, brush cleanup, tree planting and trellis system installation continue as growers continue to finish early season tasks. Commercial bumble bee and honey bee hives were removed from some orchards after king bloom pollination. For other orchards, commercial hives remain for pollination as bloom lingers (Figure 2).  

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, applications can be made at dusk or at night when bees are not active. Reduced risk insecticides should also be used, such as Sivanto or Grandevo.  

For some apple varieties, most advanced fruitlets are about 5-6 millimeters (mm) in the west central region. This includes early varieties such as Zestar and Idared. Golden Delicious, Honeycrisp and Gala are at petal fall. 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 or petal fall. Thinning early can be particularly important for varieties, such as Honeycrisp, that initiate flower bud development for the following season shortly after bloom. Early thinning for varieties like Honeycrisp can result in higher return bloom. More information on thinning strategies for Honeycrisp can be found here: Honeycrisp Crop Management for 2022. Additional information and thinning recommendations can be found in the MSU Thinning Guide. 

According to the Cornell Apple Carbohydrate Thinning Model, the estimated carbohydrate balance (six-day weighted average) over the past week for Hart has been above 0 balance or just under. Therefore, the risk of overthinning is low, and the model recommends increasing the chemical thinner rate by 30%.  

RIMPro forecast is predicting that apple tissues are at a slight risk for apple scab infection on May 16 and 17. Scab spore release is gradually increasing in Oceana County, and most ascospores are mature and have been released at this time. Warmer weather this weekend means that the scab fungus, Venturia inequalis, will be more active and can infect new leaf tissue faster compared to days with cooler temperatures. With rapid tree growth in our region, adequate fungicide coverage is key to minimizing apple scab infection. Coverage is also important for pear blocks in the region for pear scab (Venturia pirina).  

Fire blight risk has been generally low this spring, but vigilance is needed to 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 epiphytic infection potential (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 for fire blight prone blocks with historically high pressure and fire blight sensitive varieties such as Ginger Gold, Fuji and Gala.  

Tart and sweet cherry are shuck split or green fruit stage. Cherry leaf spot management is needed to protect leaves against infection. Although there have been many rain events this spring, according to the Hart Enviroweather station, only two events have led to infection on April 27 and May 7-8. For rain events, the duration of wet hours has not been high enough to result in infection.  

Peaches are at petal fall or shuck split depending on the variety. Venture peach trees are at shuck split at the West Central Michigan Research and Extension Center. 

Pear varieties range from late petal fall to early fruit set for varieties such as Bartlett, Gem and Cold Snap. The largest bartlett fruitlets at West Central Michigan Research and Extension Center were 4-5 mm in diameter. 

Plums are at fruit set. Apricots are growing rapidly. 

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 will continue to rise over the next few weeks. Plum curculio and codling moth have not been observed yet, but they should be more active over the next week.  

Early season pests 

On May 13, 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 on May 13 with an average of 66.7 moths per trap). Codling moth was trapped with an average of 20.7 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. 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 are flying in the region. 

Rosy apple aphid is a common pest in our region. Scout for eggs on the bark of apple trees and check for colonies in fruit clusters to determine if treatment is needed.  

Obliquebanded leafroller larvae have been observed in Oceana County. Nontarget adult leafrollers may end up in obliquebanded leafroller traps since they are also attracted to the same pheromone blends. Be sure to positively identify obliquebanded leafroller adults when they arrive, likely in July. 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 few weeks. Continue to monitor this minor tree fruit pest.  

Oriental fruit moth was trapped at three locations in Oceana County with an average of 36 oriental fruit 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 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.