West central Michigan small fruit regional report – August 19, 2014

Spotted wing Drosophila continues to show up in all berry crops. Growers need to intensify their monitoring efforts.

Weather conditions in west central Michigan have remained very stable for the past two weeks with minimum changes on the daily temperatures. The average daily maximum temperature for the past seven days was 74 degrees Fahrenheit and the minimum was 55 F. Rain was at a minimum with no more than 0.5 inches accumulated during this period.

Currently, blueberries are the main small fruit being harvested. However, there are small quantities of fall raspberries and day-neutral strawberries that are also being harvested. In blueberries, growers are finding it necessary to apply supplemental irrigation given that during the past seven days, only a small amount of rain accumulated in the area. Although in some parts of the state there was extensive flooding, in west central Michigan the precipitation reached only 0.29 inches. Problems resulting of lack of rain are shriveling of fruit and difficulties for mechanical-harvested blueberries; berries are more difficult to shake from the bush.

Even though there has been only a small amount of precipitation, the combination of high relative humidity in the area with heavy dew in the morning is bringing some problems with Alternaria fruit rot in blueberries. The same environmental conditions are creating problems in strawberries and raspberries. There are reports of fruit rots in strawberries and raspberries that, in conjunction with spotted wing Drosophila (SWD), will create problems for small fruit operations such as U-pick farms.

For all small fruit crops, major problems observed at this time are SWD, fruit rots and labor issues, but SWD remains the main issue. For the past two weeks, there has been a three-fold increase in the populations present in all fields monitored by Michigan State University Extension, with substantial fruit infestation observed only in raspberries. Only in one instance a grower has reported fruit infestation in blueberries that showed symptoms of decay.

Although SWD is currently trapped in strawberries, no fruit infestation has been reported. However, a year ago at the same farm, the crop was abandoned due to heavy SWD infestation. Growers need to intensify their monitoring efforts including checking monitoring traps, inspecting the fruit before and after any insecticide application, and repeating the insecticide application after any rain event.

Current daily temperatures are optimum for good SWD control with pyrethroid insecticides; cool temperatures favor the effectiveness of pyrethroids against SWD. Malathion 8F is also favored by the current weather conditions and will be more persistent and effective than when applied under high temperatures.

Because the temperatures have been relatively cold in relation to 2014, we are seeing some Alternaria fruit rot infestations in blueberries that may be mistaken for SWD infestations. The same has been observed in raspberries and strawberries. In order to avoid making a mistake and applying the wrong control products, check fruit with symptoms of decay using the recommended methods – saline solution, boiling water, etc. – to verify that no SWD infestations are present. If SWD are present, apply the recommended corrective measures immediately. Otherwise, use only the recommended fungicide to treat the fruit rot infections.

Remember to make sure you take into consideration the weather conditions at the time of the application and during the expected protection period. Check the weather and if the daily temperatures or rainy conditions may affect the durability of the insecticide you applied, repeat the application with a different insecticide. For insecticides and doses for blueberries, see “SWD Management Recommendations for Michigan Blueberry.” For insecticides and doses for raspberries, see “Spotted Wing Drosophila Management Recommendations for Michigan Raspberry and Blackberry Growers.”

Contact your nearest MSU Extension county office or Carlos Garcia at 616-260-0671 or garcias4@msu.edu for assistance.

Did you find this article useful?