By Carlos Garcia-Salazar
Temperatures continue pushing the small fruit season to an early beginning. Start preparing your IPM program to manage fruitworms and early-season diseases in blueberries.
Current weather conditions in west central Michigan remain above normal. Daily temperatures for the past seven days have been on average 54 degrees Fahrenheit. Minimum temperatures for the same period average 44 F and the maximum temperatures average 64 F.
No water deficit has been reported. Although there were a few snow days during the past winter season, rainy days have compensated for the lack of snow. Current rainfall accumulation since Jan. 1, 2017, is 9.7 inches with 1 inch accumulating during the past seven days.
The prevailing weather conditions have advanced the seasonal phenology of plants, as well as insects and diseases that affect small fruit crops early in the season. It is important to prepare your integrated pest management (IPM) program now to control those problems in time and prevent damage later on.
As of April 18, the blueberry crop phenology is moving along very fast. In Allegan County, for example, early varieties are already in the tight cluster and pink bud stage. Other varieties like Bluecrop are in the late green tip stage (0.25–0.5 inch green).
Early-season blueberry disease management
Although no significant risk of spring frosts is in the extended weather forecast for this region, cool temperatures and morning dews provide good environment for outbreaks of mummy berry and botrytis twig blight. If you did not apply any dormant spray against the mummy berry, this is the time to start your applications to prevent shoot strikes and green fruit infections.
Preventing mummy berry infestations during the pre-bloom period limits the risk of further infections of green fruits. Pollinators, mainly honey bees, are attracted to exudates from shoot strikes and they can carry the mummy berry spores to flowers after they visited infected shoots. Currently, mummy berry preventive applications are recommended with Indar, Orbit, Quilt Xcel, Prolin and Ziram, among others. (Please consult Michigan State University Extension’s bulletin E0154, “2017 Michigan Fruit Management Guide,” for more fungicide options and recommendations.) If in the past your fields presented problems with botrytis twig blight, Ziram will be effective against both Mummy berry and Botrytis.
Early-season blueberry insect problems
Cherry fruitworm and cranberry fruitworm are the major concern. Insects will start arriving earlier because of the mild winter we experienced this year. We expect an early emergence of overwintering populations of cherry fruitworm, especially in counties south of Allegan County.
According to our cherry fruitworm degree-day model, we are expecting first overwintering adults to emerge in the region around 238 degree-days accumulated since March 1. As of April 18, the degree-day accumulation is on average 110 degree-days, almost halfway from the beginning of the cherry fruitworm emergence.
Below is a table with the predicted degree-days when we are expecting the emergence of cherry fruitworm and cranberry fruitworm, and the current degree-day accumulation for key weather stations in the west Michigan.
Predicted degree-days for cherry fruitworm and cranberry fruitworm emergence |
Insect | First adults | First eggs | Current degree-day accumulation (4/18/2017) |
Grand Junction | Fennville | West Olive |
Cherry fruitworm | 238±30 | 432 ± 15 | 128 | 108 | 94 |
Cranberry fruitworm | 375±20 | 460±20 | 128 | 108 | 94 |
Pheromone trap deployment should be started at 175-200 degree-days accumulated since March 1. Large, plastic Delta traps with interchangeable sticky inserts are recommended, and lures need to be attached with pins to the interior roof of the traps away from the sticky insert.