West central Michigan small fruit update – Aug. 3, 2021

West central Michigan remains under moderated drought conditions, which may affect blueberry fruit quality and yields in fields with limited supplemental irrigation.

Men taking samples from a dish filled with blueberries.
Fruit sampling to determine the presence of spotted wing Drosophila larvae in blueberries ready for harvest using the salt test method. Growers can use a fine brush to remove spotted wing Drosophila larvae emerging from the berries. Photo by Carlos Garcia-Salazar, MSU Extension.

Weather conditions in west central Michigan are passing through a seasonal dry period that has been occurring every year at least for the past five years. This period of dry weather conditions coincides with the time when blueberries are more susceptible to a water deficit that, according to Bryla from the USDA Agricultural Research Service, may reduce fruit yield and quality by as much as 35%. The water deficit created by these weather conditions remains as one of the main limiting factors for our fruit industry. In 2019, 23% of blueberry growers responding to our end-of-season evaluation survey indicated weather conditions were responsible for low yields and fruit quality problems.

Currently, weather conditions in the region are characterized by daily minimum temperatures ranging from 55 to 66 degrees Fahrenheit, and daily maximum temperatures fluctuating between 75 and 85 F. Regarding rainfall, over the past seven days there were scattered rain showers that left a precipitation accumulation of less than 0.25 inches.

In general, there have been more than 10 days without an important rainfall in the area. These weather conditions are forcing growers to provide supplemental irrigation to blueberries to maintain yield and fruit quality.

As of Aug. 3, 2021, the blueberry harvest continues without mayor problems, except for lack of labor for hand harvesting and drought conditions. Conditions are similar to the 2020 blueberry harvest season. However, yields are better than those obtained in 2020.

Present problems detected by our Michigan State University Extension fruit team and reported by growers included the presence of Anthracnose fruit rot and spotted wing Drosophila (SWD). For Anthracnose, growers are reporting infections mainly in Bluecrop fields. So far, weather conditions in the area, especially around Grand Junction, Michigan, have been optimal for fungal growth—daily temperatures ranging from 68 to 81 F and periods of wetness resulting from some localized rain showers.

Fungicides recommended for Anthracnose management include Abound, Pristine, Sil-Matrix and Switch. Those fungicides are very effective against this fruit rot and have a zero-day preharvest interval (PHI). Please check the 2021 Michigan Fruit Management Guide (MSU Extension Bulletin E-154) for doses and other recommended fungicides.

The other problem is the increase presence of SWD. Up until two weeks ago, the number of flies trapped in our regional monitoring network were minimal—less than 10 flies per trap per week. However, after the intense rains that occurred around July 23 and 24, numbers escalated rapidly to more than 20 flies per trap per week. In some cases, the numbers were more than 50 flies per trap. That situation is taking some growers by surprise who were not monitoring their fields for the presence of the pest. Their fruit is getting infested with SWD larvae and are at risk of being rejected or downgraded at the packing facilities.

Monitor your field twice a week to be aware of the presence of SWD in your berries. Check the fruit for the presence of SWD larvae using the salt test method and apply any of the recommended insecticides if you find larvae in the sample.

For growers interested in applying organic approved insecticides against SWD, Grandevo WDG and Entrust 2 SC are good alternatives. Again, check the 2021 Michigan Fruit Management Guide for the recommended products and doses.

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