MSU Extension Fruit & Nuts

Hot, humid, summer weather finally appears to be the new normal in west central Michigan as summer pushes on. We have moved ahead significantly in our growing degree day accumulations in the past two weeks, and more heat is on the forecast in the next 10 days. Our sandy soils are drying out quickly already, and there are some spots that could actually use some rain soon. The best chance of rain is currently forecasted for Wednesday, July 10, but is currently looking to be an outside chance and many locations will not see any precipitation. Irrigation is likely to go on in orchards for the first time this season in the next two weeks, especially on young, shallow rooted trees. The heat will push the region into sweet cherry harvest within the week in many locations, and tart cherries will not be far behind.

Apples continue to push strong vegetative growth with deep soils still well saturated and a nice wave of heat to work with. Summer pruning will likely be required to get good sunlight exposure into the canopy on color-shy varieties this season, and growers continue to add calcium to sprays on varieties prone to bitterpit. Hand-thinning in fresh market varieties is ongoing in blocks that are still set up too heavily. The hot, dry weather will help to slow down and dry up the shoot blight strikes that have been showing up over the past two weeks, as will applications of Apogee that affected growers put out in the past few weeks. If you see new fire blight strikes, take advantage the hot, dry weather to prune out these strikes from the trees. The strikes can be tossed in to the row during hot, dry weather like this as they will dry out and die quickly.

Apple scab is minimal in orchards this season, even in orchards with a history, indicating growers did a nice job of staying on top of the disease during primary apple scab this spring. Monitor the sooty blotch/fly speck model for 240 hours since 2 inches of rain have fallen on the last fungicide application. The dry weather in coming days is likely to keep these accumulations fairly stagnant, but if we end up getting scattered showers tomorrow, we could still see this stack up some.

Tart cherries are coloring and sizing rapidly, although we are likely seven to 10 days from harvest even in early locations in the area. Growers will be using ethephon on tart cherries in the next week in many orchards and should evaluate the size of the crop and health of each orchard prior to determining xdrates. Remember that some of the efficacy of this material is dependent on the weather within 72 hours after the application, and the rate needs to be adjusted based on considerations for the stress status and crop load of each orchard. The optimum temperature range for the application is between 60 and 80 degrees Fahrenheit, and rates will need to be dialed back if weather above 80 F continues, especially when we consider the light crop that will loosen more easily and the high prevalence of cherry leaf spot, phytotoxicity, and cherry yellows that we see this season. Stressed out trees can be adversely affected by ethephon, especially at higher rates during hot weather, so a gentle hand will be needed in many orchards this season.

Brown rot should also be on the radar for tart cherry growers, although the hot and dry weather on the forecast will help to reduce issues with this disease. As you consider your preharvest brown rot spray options, remember that SDHI's Merivon and Luna Sensation, Flint Extra and the 12 fluid ounce rate of Indar are all viable systemic products. These should all be mixed with Captan to help manage resistance.

Sweet cherry harvest will begin in the next several days. The size of the crop is decent in most orchards, but problems with fruit cracking and brown rot have become increasingly evident in the past week and are causing major headaches. Brown rot is a very difficult disease to control in the best of times, and the warm weather with repeated rain and the prevalence of fruit cracking has strongly contributed to the establishment of this disease. Once brown rot has a foothold in a sweet cherry orchard, it is nearly impossible to get back out from under the issue, and this season we can expect that the disease will continue to be a struggle until harvest is over.

Brown rot is particularly common to find in large, standard sized sweet cherries on pendant wood and well shaded clusters, where humidity is higher and duration of fruit wetness following a rain event is longer. Growers trying to keep the disease in check with applications of Indar at the highest labelled rate as well as SDHI’s Merivon and Luna Sensation. Both of these products should have Captan incorporated in to the program in order to manage resistance, but many growers are trying to dial down the amount of Captan going in to sweet cherry orchards right now due to concern over phytotoxicity.

Insect update

We saw a slight decrease in the overall number of spotted wing Drosophila (SWD) caught in the trapline this week, but the number of individual traps remained roughly the same. We have now captured SWD at all locations, and all growers in the region now have fruit, straw-colored or later, that are physiologically susceptible to SWD. Spray programs for SWD were initiated in most locations last week and should remain in place until harvest is complete. Select only products rated “excellent” and keep intervals as close to seven days as possible.

SWD total catch by township this week:

• Pere-Marquette: 0
• Riverton: 1
• Weare: 0
• Golden: 2
• Hart: 0
• Elbridge: 3
• Benona: 0
• Shelby: 1
• Clay Banks: 2
• Grant: 2
• Walkerville: 1
• Summit: 0
• Fremont: 4

Flight of the first generation of codling moth continues at high pressure sites, and early adult flight and larval activity are ongoing. We have accumulated between 400 and 600 growing degree days (GDD) base 50 since biofix, depending on orchard. Codling moth biofix dates were highly variable this year.

Flight of the first generation of oriental fruit moth is over, and the flight of the second generation will likely begin in the next two weeks. Shoot feeding can now be observed.

Plum curculio activity is likely over for the season as we move in to mid-July and fruit continue to size.

Flight of greater and lesser peach tree borer is nearing an end. Lorsban should have already gone out in sites of concern.

The first flight of obliquebanded leafroller is ongoing at this time, with strong activity being reported at many locations. Make sure you are trapping this pest in sites with a history so that an accurate biofix can be set for the block for management down the road. Egg hatch will begin 400-450 GDD base 42 after biofix, so this mark should be the target start date for insecticides targeting summer obliquebanded leafroller.

European red mite numbers are starting to build now that weather is turning hot and dry. Begin checking orchards carefully for mite pressure to inform summer miticide decisions. The treatment threshold for European red mites is five to seven mites per leaf through July.

San Jose scale flight is over and crawler activity is nearing an end. We are past the optimal timing for targeting crawlers this year.

No apple maggot activity has been reported yet and it’s still early, but this upcoming stretch of hot, dry weather will move us ahead in growing degree days to the point where the next good flush of rain is likely to bring a few out, especially at sites with a history. Think about getting traps up in the next week or two.

Brown marmorated stink bug traps continue to be empty. Activity is low at this time.