West central Michigan small fruit update – July 24, 2018

Blueberry harvest is underway with very good quality fruit and without major issues related to insect or disease problems.

Western Michigan has seen more than two weeks of summer drought with only scattered rain showers producing less than 0.5 inch of precipitation, and daily temperatures reaching the upper 80s. For the last seven days, the average daily high was 80 degrees Fahrenheit and the average daily low was 60 F.

Although precipitation in west central Michigan was less than 1 inch over the past seven days, in the southern part of Allegan and in Van Buren counties accumulated precipitation in a lapse of two days ranged from 2.2 to 3 inches of rain. This uneven rain distribution is creating problems for blueberry growers. On one hand, fields located in counties north of Allegan County require supplemental irrigation to maintain fruit quality at fields close to harvest or where the harvest has started. Also, for fields with varieties that start coloring, supplemental irrigation ensures good fruit growing conditions. On the other hand, too much rain interferes with harvest, which is in full swing in fields at the southern end of Allegan and at Van Buren counties. It also increases the risk of fruit rots and outbreaks of spotted wing Drosophila (SWD) fruit infestations.

In general, small fruit conditions for raspberries include growers limiting the planting of summer-bearing varieties to avoid SWD fruit infestations. Thus, most raspberry fields in west central Michigan are fall-bearing varieties. Currently, raspberries in the area are in the green fruit stage without much problems associated with diseases or insects. On the other hand, strawberries have been renovated. It was a very short harvest season with small fruit and not so good quality. Spring frost and high summer temperatures were responsible for this year’s crop failure.

For blueberries, the harvest of mid-season varieties has continued, mainly Bluecrop and Duke. Draper was severely damaged by winter and spring frost at some fields north of Allegan County and only small amounts of berries will be harvested. Yields for Bluecrop and Duke were affected by winter subzero temperatures occurring in January and February. Those temperatures caused extensive bud damage and bud kill that left many plants with plenty of flowers but no leaves at the end of May. That particular problem is more pronounced in fields far from Lake Michigan shorelines.

In addition to damage in varieties mentioned above, one particular observation offered by some growers is that Elliott was seriously affected by the same environmental problems and bud kill was extensive. Jersey seems to be the only variety in good shape.

It is important to notice that many fields that presented low fruit set this season are the same fields that four to five years ago were severely affected by winter. Those fields are not completely recovered from damage suffered during those winters.

Regarding insect and disease problems in blueberries, SWD continues emerging in large numbers, especially at fields located near woods or unattended fields. This season, we are seeing that summer temperatures (maximum daily temperatures averaging 84 F) had a substantial impact on the population dynamics of the SWD. At the same time, limited rain during June (accumulation of less than 3 inches) and during the first 15 days of July (accumulation of less than 0.6 inch) created relative humidity (rH) unfavorable conditions for the survival and reproduction of SWD. These two combined factors provided a very welcomed break for growers that have been able to manage SWD infestations with relatively easiness.

However, these conditions are changing. Temperatures and rains from the past days are providing a relief for the SWD, which will start laying eggs at full capacity under conditions of ripe fruit, favorable temperature and rH.

If you sprayed during the past Friday or Saturday, July 20 and 21, reapply fields if rain accumulated in their area was more than 0.5 inch. Neglecting the weather conditions, especially rain and temperature, after an insecticide application could be very problematic. Fruit infestations may result at harvest time.

Remember, select the best insecticide according to prevailing and forecasted temperatures and precipitation. 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 insecticides (except Brigade) if the temperatures are above the mid-80s or 90s. If you do, repeat the application five days later instead of seven days after the first application. According to Michigan State University Extension entomologist Rufus Isaacs in 2015, the mean life of Mustang Maxx is three days under “normal” temperatures. Thus, the insecticide effectiveness will decrease substantially during the following three to four days.

Check the weather forecast for rain before spraying; Lannate and Brigade are excellent under conditions of high temperatures and precipitation. Mustang Maxx is excellent if temperatures are below the mid-80s and there is rain in the weather forecast. For more options, check the “2018 MSU Fruit Management Guide,” MSU Extension bulletin E0154.

If you need assistance with your SWD management program, visit the nearest MSU Extension county office or call me at 616-994-4580 for assistance.

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