By Amy Irish-Brown
Crop development
Tree development continues to move in a nice, even pace with no explosion of growth for the most part. Bloom of all tree fruit species appears to be very healthy this year, most likely due to mild winter conditions. Early developing apple varieties (Ida Red, Gingergold, Zestar) are in the pink to first bloom stage with some warmer sites in king bloom. Late developing apple varieties (Rome, Spy, etc.) are still in the tight cluster stage. Sweet cherry are now blooming with only the latest varieties not quite in full bloom yet. Peaches are in full bloom for the most part.
Cooler weather over the past weekend had a few frost fans running the morning of April 22, but temperatures just dipped to the 32-degree Fahrenheit mark for the low spots. There was nice inversion according to the new 20-meter tower at the Sparta Enviro-weather station. The critical minimum temperatures for tree fruits should be in the 27-28 F area right now for most species and varieties.
Diseases report
Heavy rainfall on April 20 resulted in a light apple scab infection according to most Grand Rapids, Michigan, area weather station data. Ascospore discharge numbers were extremely high with this latest rain event and they are expected to be even higher with the rains predicted for later in the week. Typically, the highest spore releases come between tight cluster and petal fall. Temperatures will be warm coming into the rain on Wednesday and Thursday, April 26 and 27, and cool off toward the weekend. These weather conditions will be ideal for apple scab and spore numbers will be high. Full cover fungicide programs with protectants and systemic action are called for.
The several days of rain predicted for later this week will be ideal for powdery mildew to establish. This is the time to add a mildewcide in the program for the next few weeks to prevent shoot and fruit infections.
Fire blight now becomes a concern with open bloom present. There will be a risk for blossom blight infection from the rain predicted for later this week, and Michigan State University Extension suggests covering open bloom for infection potential. You can track fire blight risk via the MSU Enviro-weather website for the weather station nearest you.
There are two models on Enviroweather for fire blight—the Fire Blight of Apple Blossoms (Sparta) and the Interactive Fire Blight Predictor (Sparta), where you can manipulate the data and try out different weather scenarios. You can also download the MaryBlyt Fire Blight Model and add your own data to be saved on your computer.
Pest report
We are in the pink window when you get a chance to protect from rosy apple aphid, green fruitworm and overwintering obliquebanded leafroller—all of which are present in low to moderate numbers in apple orchards in west Michigan. Minor pests also active at this time are spotted tentiform leafminer and redbanded leafrollers. Spotted tentiform leafminer continue to fly in very low, but increasing numbers, and a few redbanded leafroller adults are present, but of little concern.
Black stem borer made an appearance about a week ago with the warmer weather. Monitor blocks of stressed apple trees for these beetles burrowing into trunks and treat in blocks of concern.
If you had high levels of San Jose scale on fruit at harvest in 2016, please consider tightening up your management program for this pest. There are several chemistries that can be used in the pre-bloom apple period to help reduce the eventual number of crawlers. Every year for the past five or six years, I see more and more scale on fruits in the bins.
By the time I write again next week, we will be in full bloom. Bees will be present in our orchards and their health will need to be considered before all plant protectant applications are used.