West central Michigan small fruit update - July 3, 2018

Intense heat wave affecting the state is causing problem for small fruit growers, especially for blueberry fields ready for harvest or that started harvesting. Sunburn on ripe fruit clusters is creating problems at harvest time.

West central Michigan has been under a heat wave that created problems for small fruit growers, especially for growers that lack irrigation systems and rely on rainfall for irrigation. During the past seven days average minimum temperatures in the region have been 65 degrees Fahrenheit and the average maximum 83 degrees Fahrenheit. Accumulated precipitation over the same period reached 1.7 inches. But most of the precipitation occurred on one day and the rest were only scattered rain showers producing less than 0.6 inches of accumulation.  

There is not a high probability of rain during the rest of the week, and forecasted temperatures for the next six days are in the upper 80s and low 90s.  This is a difficult situation for growers with limited availability of water to provide supplemental irrigation for blueberries. In addition, prevailing weather conditions in west central Michigan may difficult the spotted wing Drosophila management. This pest is already present in high number at blueberry fields in Allegan and Van Buren.

Since the blueberry harvest is already in progress in Allegan and other southern counties, it is important to make sure that fruit quality is maintained in spite of the current adverse weather conditions. So, we recommend;

Maintain your field well irrigated. That is especially important for middle to late season varieties still in the late green fruit stage. Remember, fruit growth is controlled by fruit cells expansion due to increased water content. If no supplemental irrigation is provide at this critical time, the fruit will not grow and ripening fruits will start shriveling.

Check for soft fruit. High temperatures currently affecting the region may cause ripe fruit to become soft due to lose of water. Make sure that fruit softness is not caused by Alternaria fruit rot. Fruit affected with Alternaria looks soft, but one side of the fruit shows a sank area around the fruit crown, and it may be possible to observed a grey mold at the center of the affected area.

Install SWD monitoring traps. It is important the deployment of monitoring traps for early detection of the arrival of SWD flies. Blueberry field with more than 5 percent fruit in the blue stage or that just started coloring are at risk of early SWD attack if flies are undetected or unattended. Detecting the early fly arrival is critical for a successful SWD management.

Select the best insecticide according to prevailing temperatures and precipitation. Growers need to be aware that knowing when to spray, what to spray based on the characteristics of recommended insecticides, plant conditions, and the prevailing and forecasted weather conditions is basic for a successful SWD management.  If you are harvesting and SWD flies are detected in your field, DO NOT wait to find infested fruit. Stop harvesting and spray immediately. Do not use pyrethroid insecticide (except Brigade) if the temperatures are above the mid-80s or 90s. If you do, make sure to repeat the application five days later instead of seven days after the first application. According to Rufus Isaac (2015), the mean life of Mustang Maxx is 3 days under “normal” temperatures. Thus the insecticide effectiveness will decrease substantially during the following 3 to 4 days.

If growers require assistance with their SWD management program please visit the nearest MSU Extension office or call Carlos Garcia at Ottawa County Extension 616-994-4580 for assistance.

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