Northwest Michigan fruit update – July 23, 2019

Sweet cherry harvest is underway and tart cherry harvest will begin later this week. Spotted wing Drosophila numbers have increased exponentially over the last week.

Wounds from spotted wing Drosophila on Ulster sweet cherries
Wounds from spotted wing Drosophila on Ulster sweet cherries at the Northwest Michigan Horticulture Research Center on July 22, 2019. Photo by Emily Pochubay, MSU Extension.

Weather report

The weekend brought in some storms and most of the region received significant rainfall. We have not yet heard if the storms caused any damage—we’ll take that as good news! The rainfall across the region was variable on Saturday, July 20. The Northwest Michigan Horticulture Research Center received just over 0.75 inch of rain, and Bear Lake, Michigan, received almost 5 inches of rain! The Kewadin Enviroweather station received less than 0.25 inch of rain. The rain brought cooler weather, and daytime temperatures are currently in the mid-70s, which is much better for harvest than the 90 degrees we saw on Friday. According to Michigan State University's Enviroweather, we have accumulated 1,754 growing degree days (GDD) base 42 and 1,090 GDD base 50.

Crop report

Sweet cherry harvest has begun across the north. Some growers started to shake brine with stems last week, and traditional sweet cherry harvest is underway this week. We have observed cracks in the sweet cherries with the recent rains, and American brown rot will be a challenge if there are cracks in the fruit. The warm and humid conditions have made disease control challenging this season. We have also heard that if growers controlled brown rot, fruit quality has been good.

Growers are putting Ethrel on tart cherries, and some growers expect to start harvest later this week and into next week.

Pest report

In addition to harvest, growers have been busy recovering orchards that have yet to be harvested following rain over the weekend. The most pressing concerns in cherries have continued to be American brown rot and spotted wing Drosophila (SWD). Fortunately, there is a stretch of drier weather ahead and dew points are predicted to be lower, meaning that the humidity for the coming days should be less than we have experienced recently; these conditions will be helpful for harvest crews as well as for implementing pest management strategies.

American brown rot has continued to be problematic this season. However, in orchards where this disease has not escaped control, fruit have good size and quality so far this season. We have observed cracks in sweet cherries following rain over the weekend and cracked or otherwise damaged cherries are very susceptible to brown rot.

Tart cherry orchards with good growth this season are starting to look better in terms of cherry leaf spot infections. Growers have been diligent with preventative control measures for cherry leaf spot and this hardwork is paying off. In orchards where new growth is limited, however, many leaves that were infected with cherry leaf spot early in the season have defoliated. At the research station, there are older, low vigor blocks with very few leaves remaining and fruit that have stopped ripening.

We reported in our FruitNet newsletter on Friday that 100% of traps in the northwest region caught SWD last week and trap numbers are rising. Yesterday, we checked the 40 traps at the station; again, we found SWD in all these traps and a total of 4,405 SWD—that is eight times as many SWD in traps at the station this week compared with a week ago. In addition to high trap numbers, we have found larvae in many of our cherry samples from the station. Some of these samples were not treated with insecticides, but we have also found larvae in sweet and tart cherries under minimal spray programs.

Wounds from SWD infestation are especially noticeable in unsprayed sweet cherries at the station (see photo). With such high SWD populations already this season, keeping fruit covered using full rates and tight intervals and recovering after rainfall through harvest is critical. We will continue to check SWD traps throughout the region over the course of this week and report numbers in the FruitNet email newsletter.

We have not detected cherry fruit fly at this time.

American plum borer, lesser peachtree and greater peach tree borer activity is ongoing, but there have been low catches of greater peachtree borer at the station so far this season.

San Jose scale crawlers are still active and settling in new feeding sites at the station.

Obliquebanded leafroller activity is ongoing and we are finding moths in both apples and cherries at the station. Since biofix (June 30), we have accumulated 654 GDD base 42, which indicates that about 50% of eggs are hatching. Small larvae can be found and by the end of the week, larvae should be big enough to see more easily.

Codling moth flight continues to be steady at the station. Since biofix (June 8), we have accumulated about 792 GDD base 50 and we are past peak egg hatch of the first generation.

While we have not caught apple maggot in our traps, we have surpassed the 900 GDD base 50 since Jan. 1 mark, which estimates that this pest should be emerging from the soil soon. This pest typically emerges following a heavy rain, so it is possible there could be apple maggot activity in some orchards following last weekend’s rain. Red sticky sphere traps baited with apple essence are the preferred trap for this pest.

Tender new growth on apples has been favorable for aphids and leafhoppers. Keep an eye out for these pests on new plantings that may not have regular cover sprays.

Traps for brown marmorated stink bug have been deployed, but we have not yet detected this pest in traps in our region. Adult brown marmorated stink bugs have been active in urban areas and adults found up to this point in the season are those that overwintered. Keep an eye out for injury on fruit that could be brown marmorated stink bug feeding damage as well as for nymphs. We don’t often catch this pest in the act of feeding and by the time damage is visible, the bugs have left the scene.

Rose chafers have winded down, but we have observed an uptick in Japanese beetle activity.

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