MSU Extension

As of May 17, 2016, weather conditions in the central region are characterized by low temperatures and some periods of rain or drizzle that favor disease development in blueberries. So far, temperatures have been around the low 60s with a minimum temperature of 44 degrees Fahrenheit and a maximum of 60 F. Those conditions have allowed a degree-day accumulation of 228 degree-days base 50 F for Michigan’s central region area.

Regarding plant development, blueberries continue in the bloom stage in all the central region. Blueberry bloom stages go from full bloom in early varieties such as Bluecrops, Duke, Brigitta, etc., to 10-20 percent bloom in late season varieties such as Elliott.

Pollinator bees are out in most fields, but some small production growers are having problems getting bees for their farms. Given the increased need for bees during the bloom period and problems associated with colony collapse, which has reduced the availability of bee colonies at critical times, growers will have to contract the service early in the season in the future to avoid problems in getting them on time.

Regarding blueberry diseases, so far no mummy berry shoot strike has been reported despite the weather conditions that, for the past five days, were conducive for disease development. Currently, some growers are applying the second fungicide application, but for the most part, growers already completed the early disease control program.

For early insect pest management, prevailing weather conditions delayed the emergence of fruitworms. However, cherry fruitworm started emerging during the past five days in blueberry fields around the Fennville-Grand Junction, Michigan, area. Our degree-day model predicts cherry fruitworm emergence around 238 degree-days base 50 F cumulated since March 1. Cherry fruitworm emergence in Van Buren and Allegan County blueberry fields occurred during the past five days in agreement with the model prediction. However, north of Allegan County, no emergence has been reported; however, according to our degree-day model (see table below) the emergence is expected for the next five to seven days.

There has been no cranberry fruitworm emergence. According to our degree-day model and the extended weather forecast, its emergence has been delayed and its emergence in the central region is still more than a week away.

If you are trapping cherry fruitworm and your early varieties are in full bloom or petal fall has started, do not wait for cranberry fruitworm emergence to start your fruitworm control. You will need to cover the window between cherry fruitworm and cranberry fruitworm emergence to prevent fruit damage. So, your first insecticide application will control the early cherry fruitworm attack and a second application will complete the fruitworm control program targeting cranberry fruitworm.

Some important considerations for fruitworm management at this time are selecting the correct pheromone traps and management. Successful fruitworm management depends on the following factors.

• Use a monitoring program for pest distribution and biofix.
• Use the GDD model for improved spray timings.
• Use insect growth regulators insecticides for selectivity for use during bloom.
• Use reduced-risk insecticides for control of fruitworms and other overlapping pests.

Despite years of training and multiple recommendations about the correct way to deploy and maintain the pheromone traps, trap placement and servicing traps are still a complex problem for some growers. The Michigan State University Extension recommendation are:

• Use large plastic Delta traps with interchangeable bottoms that allow an easy cleaning of dead moths and insects that may reduce the effectiveness of the trap.
• Do not place the pheromone lure onto the sticky bottom of the trap. Lures need to be secured with a pin and attached to the interior top of the trap. Dropping the lure onto the sticky bottom will prevent the release of the correct amount of pheromone from the lure. Over time, the lure will become coated with tanglefoot by rolling over the bottom of the traps every time the trap swings due to the wind effect.
• Do not place cherry fruitworm and cranberry fruitworm side by side. There is a pheromone interference that will prevent the approach of the moths to the trap. This will decrease its efficiency and will give you false information on the presence of fruitworms in the target area. Place traps at least 30 feet apart.
• Place your traps in your early varieties as they are the ones that need immediate protection.
• Use a number of traps according to the size of your field. For better results, MSU Extension recommends placing at least one trap per 5 acres.

If you need assistance with your fruitworm control including selecting insecticides or using MSU Enviro-weather, please call your nearest MSU Extension county office or contact me at 616-260-0671 or garcias4@msu.edu.