Northwest Michigan fruit update – Aug. 21, 2018

The weather in the northwest continues to be hot and dry.

Weather report

Temperatures are lingering in the 80s and overnight temperatures are in the mid-50s to low 60s. There has also been significant cloud cover for the past few days. We have accumulated 2,672 growing degree-days (GDD) base 42 and 1,782 GDD base 50.

There has been very little rainfall in the month of August. We did receive 0.4 inch of rain at the Northwest Michigan Horticulture Research Center Aug. 6, but no other Michigan State University Enviroweather stations in the region received that amount of rain. Conditions are extremely dry and trees without irrigation are showing drought stress.

There is some potential rain in the forecast today, Aug. 21, and some rain was falling this morning in Manistee and southern Leelanau County. MSU’s climatologist Jeff Andresen forecasted that the remainder of the week would be slightly cooler but then heat up again over the weekend. There is little rain in the forecast.

Crop report

Tart cherry harvest is over in northwest Michigan. The last raw product report from the Cherry Industry Administration Board had northwest Michigan at 108.4 million pounds with 2.5 million diverted pounds. Our estimate for the region was 150 million pounds; we will likely pick out much shorter than this estimate. Although the crop was shorter, the quality was excellent even with the sustained heat this summer.

Apples are coloring, but not as much as we would like as a result of the warm temperatures. Apple size may be an issue, particularly in blocks with no irrigation.

Apricot and peach harvest is underway and some peach blocks without irrigation did not size well this season. Fruit quality remains good across the board.

Tart and sweet cherry trees are showing drought stress. There is a lot of yellowing leaves, particularly on younger trees. We are also seeing firing in tart cherries. There is a high mite population across the state, and the mites are likely contributing to the firing in conjunction with the heat and drought.

Pest report

Although the forecast suggests we could receive some rainfall in the coming week, the long range forecast for the end of August and early September is calling for mostly dry and warmer than normal temperatures according to Andresen. These conditions will continue to favor mite and scale development, as these pests thrive in warm and dry seasons.

Most tree fruits in our area have had high mite (e.g., twospotted spider mites and European red mites) populations this season. Bronzing and leaf loss are noticeable, and as mentioned previously firing of branches and larger limbs are evident in tart cherries. Many growers have applied at least one application of a miticide this season with varying results; some blocks may need another application if the mite populations rebound.

Due to high pest mite populations, we have also observed many predatory mites. High infestations of mites in conjunction with ongoing powdery mildew infections could pose challenges with premature leaf loss and early defoliation of trees will reduce their winter hardiness.

San Jose scale flight is ongoing and numbers have continued to be high; this trend is consistent with other regions of the state. Crawlers began emerging within the last week, and some of the crawlers that emerged first have settled on new feeding sites. Anecdotally, we have observed crawler activity seems to be a few days ahead in apples compared to activity in sweet cherry.

We did not detect apple maggot at the station and we received reports of lower catches in the region this week. If you are using non-baited red spheres or ammonium baited yellow sticky boards, the threshold for treatment is one fly as these traps are less attractive to apple maggot compared with a volatile baited red sphere. Additionally, after reaching this threshold, make applications within a week to 10 days.

Because volatile baited red spheres are more efficient for trapping apple maggots, the threshold is higher—four to six flies per trap. As fruit begin turning color, yellow apple maggot traps are less attractive than ripening fruit. Hence, the red sphere traps can provide a better assessment of apple maggot activity in blocks with ripening fruit.

Apple maggot activity is ongoing in more southerly regions of the state at this time. With rain in the forecast, it is possible we could see a flush of apple maggot activity.

Second generation codling moth flight is ongoing, albeit the numbers in our traps at the station seem to be on the decline. Based on degree-day accumulations, we are past peak emergence at this time and egglaying is ongoing.

We have found very few brown marmorated stink bugs in traps placed adjacent to commercial orchard blocks thus far this season. However, we have had consistent catches of adults and nymphs in our residential trapping site in southern Leelanau County.

We have received several reports of native stink bug activity in orchards, and we have observed stink bug feeding damage. While some native stink bugs are predators (e.g., spined soldier bug), others like the green stink bug and Euschistus spp. feed on a broad range of hosts including fruit crops.

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