West Michigan tree fruit update – May 15, 2018

Tree fruits are all abloom this week.

It’s amazing, but after being three weeks behind in growing degree-days (GDD) a month ago, we are now only three days behind in the general Grand Rapids, Michigan, area. Plants have responded to the warmer weather and ample rainfall, but growth has been steady. Early blooming apple varieties are in full bloom and nearing king bloom petal fall. Mid-season apples are in king bloom to nearly full bloom. Later season varieties are still in the pink stage. Many sweet cherry varieties are in full bloom with early flowering cultivars in petal fall. Peaches are in full bloom. Plum and apricot bloom is ending, and fruits are still in the shuck.

Apple diseases

There have been three or four wetting periods in the last week, depending on location. Rainfall totals have been around 2 inches, but variable from south to north. Apple scab primary spore releases have been huge as is typical during the tight cluster to bloom period. The first infection from May 1 could begin to express lesions any day, so carefully scouting to watch for primary scab in apple orchards. It is likely that we are about 50 percent of the way through the overwintering primary spore load, and cover sprays are still very crucial to protect small developing apples for at least three or four more weeks. We are currently in the midst of the latest wetting period, which is a scab infection. For the latest information for all Michigan State University Enviroweather stations in our area, check out the regional disease report.

The high relative humidity levels over the past several days will favor the development of powdery mildew in apples and other tree fruits. Be sure to have something in the tank for mildew to prevent infestation of fruits and leaves.

Fire Blight is a concern for any blocks with open bloom when temperatures move above the average of 60 degrees Fahrenheit. It’s been a little too cool over the past weekend to trigger a blossom blight situation, but that will change for the next rain events predicted for the coming weekend. Temperatures are forecasted to be near 80 F and there will be much more bloom opening over the next several days. This scenario sets us up for ideal conditions for bacterial doubling and the risk could be very high for blossom blight infections with the next rain event. You can track fire blight 24/7 with the MSU Enviroweather Fire Blight model.

Apple insects

Most tree fruits now have bloom open and bees have been working hard to pollinate your crop. No insecticides are warranted at this time. Get traps and mating disruption up for codling moth and oriental fruit moth if not already. Oriental fruit moth began flying sporadically about 10 days ago with more steady flight late last week. A regional biofix has been set for May 10 (272 GDD 45). Egg hatch will begin soon and the target of 10 percent egg hatch for first cover sprays in stone fruits will fall early next week or around May 20 or 21.

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