MSU Extension

The Memorial Day weekend was pleasant for both tourists as well as the growers here in northwest Michigan. Daytime temperatures were in the mid-60s and we hit the low 70s on Monday, May 27. Each day was sunny with little wind in the mornings, and growers took advantage of these conditions for spraying. We have not received any precipitation since May 23, but the forecast is predicting rain today (May 28) and into tomorrow. We did have some cold overnight temperatures on Friday and Saturday nights (May 24-25), and the East Leland site was the coldest Enviro-weather station in northwest Michigan. Frost fans were running in many locations on both nights. We have accumulated 512 GDD base 42 and 283 GDD base 50 so far this season.

Apples. Growers are covering up for apple scab and powdery mildew with the rapid shoot growth in apples. We were at green tip on April 29 here at the Northwest Michigan Horticultural Research Station (NWMHRS), and according to the apple scab model, 90 percent of the apple scab spores are mature and 59 percent of the spores have been discharged. This model suggests that we still have a ways to go before we can call the end to primary scab. With the majority of spores at maturity, the predicted rains in the coming two days will discharge many of the spores. Growers should be sure to put on a protective scab spray prior to the rains. As of today (May 28), we have not observed scab in any apple orchards.

Today is cooler than what was originally in the forecast, so the fire blight model is not predicting a fire blight infection until Thursday, May 30, but the EIP levels will be very high. By Thursday, the EIP is predicted to be in the mid-200s with a 71 percent chance of rain. All growers with open apple blossoms will need to be protected against fire blight by Wednesday evening.

Growers in Antrim, Leelanau and Grand Traverse are highly encouraged to use Kasumin since Michigan State University Extension researchers have detected streptomycin-resistance fire blight bacteria in these three counties. The time for Apogee applications is also here, and many blocks are at king bloom petal fall. This spray is highly recommended for shoot control, but also to minimize fire blight infection.

Lastly, growers need to start their thinning program as recommended by MSU Extension educator Phil Schwallier; nibble thinning is the best method for good thinning this year. Growers should be starting their thinning program at petal fall, which is now or close to now, rather than waiting until 10 millimeters.

Cherries. No cherry leaf spot lesions have been detected in the region, but growers should be protected against the next rains with the warm temperatures. The conditions will be conducive for a cherry leaf spot infection, and there is a lot of new growth on the trees that will need to be covered. We are approaching shucksplit and into first cover; tart cherry trees will also need to be protected against powdery mildew. Our data show that this early season timing is the best way to protect against powdery mildew; once we can see the white mycelium on the leaves, it is too late and we do not have materials that will eradicate a powdery mildew infection.

Materials that have work against both cherry leaf spot and powdery mildew are recommended at this first cover timing. The newer materials are best used at first cover as they are our most efficacious products against both diseases (Merivon, Luna Sensation, Fontelis). Dodine (Syllit) is a good product for cherry leaf spot control, but will not work against powdery mildew. If growers are still in the shucksplit timing, a copper or dodine might be a good application to save the newer materials for the first cover timing. All chlorothalonil applications can also be made up until shucksplit. After shucksplit, growers that want to continue to use chlorothalonil must use Bravo WeatherStik only.

As cherries are coming out of the shuck, particularly in sweet cherries, plum curculio will be the insect to watch. The warm temperatures and predicted rainfall will cause these insects to move into orchards and begin looking for oviposition sites. For growers using the P.I.T.S. model on Enviro-weather, we were in bloom on May 16 and have accumulated only 108 GDD.

European brown rot is showing up across the region in Balatons and Montmorency. Since we are at shucksplit in most orchards, there are no control options for this disease at this time.

Sweet cherry set looks good in many blocks, but growers are concerned about pollination. When sweet cherries were in bloom we had a few good pollinating days, but we also had our fair share of cool and wet weather during this critical time. Tart cherries have just started coming out of the shuck, and we will know more about the crop next week. In the Hart, Mich., area, the tart cherry crop looks good.