Northwest Michigan fruit regional report – August 6, 2013

Tart cherry harvest continues in northwest Michigan, and cool weather has helped keep good quality fruit.

Cool conditions have helped keep the quality of tart cherries up across the region—fruit is still looking good as harvest continues for many growers in northwest Michigan. The weather has been on the cool side with day time temperatures are in the low 70s, and nighttime temperatures dip into the mid-50s. Although not beach weather, the conditions have been perfect for cherry harvest. We have had no substantial rainfall since the end of June, and soils are dry across the region. We have accumulated 2300 GDD base 42 and 1521 base 50, and these 2013 accumulations are consistent with our 20+-year average growing degree day accumulations.

Apple. Apples continue to size, and most fruit at the NWMHRC is between 45-55 mm at this time. Early varieties are starting to color with our cool nights, and Gingergold harvest is closer than we anticipated. Fruit quality is looking excellent, and most growers are pleased with their thinning efforts this spring. Some hand-thinning is still going on in blocks where there are still a little too many fruits. Apple scab is under control in many orchards, but lesions can still be found on leaves. Growers that have lesions need to protect their fruit through harvest.

Codling moth numbers are increasing in some apple blocks following two weeks of zero to few moths in traps. The increase in moth catch is likely the start of the second generation. Michigan State University Extension recommends that growers monitor each individual block rather than relying on a regional trap catch because there is tremendous variability in codling moth population size and trap catch across the region. Growers should remember to use an insecticide with a different mode of action for second generation codling moth to minimize the threat of resistance. Organophosphate resistance has been documented in codling moths (and obliquebanded leafrollers) in Michigan, and these chemistries will not be effective in controlling these pests. Pyrethroids are also not effective against these pests due to cross resistance.

We trapped our first apple maggot this week at the NWMHRC. Guthion, Imidan, Calypso, Assail, and Voliam flexi are all labeled as excellent materials against AM. The following materials are all rated good: Lannate, Provado, Bts, Belay, Baythroid, Admire Pro, Battalion and Endigo.

Cherry. Cherry leaf spot is evident in many area orchards in the tops of trees where the leaves are turning yellow and starting to drop. We recommend a post-harvest chlorothalonil spray to minimize leaf spot to keep leaves on into September. A post-harvest spray would also be helpful in controlling cherry fruit fly in 2014. Cherry fruit fly counts are very high (75+ on one trap) on some farms, and growers need to protect fruit through harvest. Spotted wing drosophila (SWD) is also a major concern as we have trapped adults in many cherry orchards across northern Michigan: Leelanau, Grand Traverse, Benzie and Antrim Counties. We also know that these flies are able to lay eggs in fruit, even if the fruit is not ripe. We have detected SWD larvae in cherries that were not protected; therefore, the potential to have infested fruit is real and cherries need to be covered through harvest. Lastly, American plum borer catch has increased from last week; we trapped 46 adult moths this week.

Wine grapes. Cool weather and the added stress of berry development have slowed shoot growth, especially in vineyards that are not being irrigated. Hedging and leaf removal is underway at many sites. Some blocks have a very heavy crop load, quite visible where the leaves have been removed from the fruiting zone!

Given the long-range forecast for continued cool weather, growers should consider reducing the crop by cluster thinning in order to keep fruit development and maturation at a good pace. This is a difficult decision if the current crop load has not been carefully estimated. See the Michigan Grape and Wine Newsletter and the 2008 Research Report to the Michigan Grape and Wine Industry Council for references for crop estimation methods.

Powdery mildew berry infections are now common at many sites, and some downy mildew has been reported. There have also been a few reports of botrytis infections on berries. Given the fact that berries are still green and hard, these infections probably are secondary to fruit injuries from insect feeding or some other sort of physical injury.

Adult Japanese beetles have now appeared in area vineyards. Their activity and injury may remain a minor problem if the cool weather trend continues.

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