MSU Extension

Weather report

As cherry harvest moves into full swing, conditions have mostly been dry. However, a brief storm that dropped a little rain moved quickly through the region Saturday, July 18. We also had some rainfall the previous Monday and Tuesday of last week, July 13-14, and the total accumulations at the Northwest Michigan Horticulture Research Center (NWMHRC) was just under 0.25 inches of rain. We had very windy conditions yesterday, July 20, with wind speeds over 17 miles per hour, and growers are concerned with wind whip in tart cherries. Daytime temperatures have typically been in the 80s with nighttime temperatures dipping into the mid-50s to mid-60s. We have accumulated 1,813 growing degree days (GDD) base 42 and 1,113 GDD base 50, and we remain three to four days behind our average.

Crop report

At this time, sweet cherry and tart cherry harvest is underway across northwest Michigan. Although we have not received substantial rain in the past week, we are seeing some cracking on multiple varieties. We have not seen brown rot in the cracked fruit with the recent dry conditions. We also have observed bird pecks on some varieties at the NWMHRC. Many growers are moving quickly through sweet cherries and blocks with light crops.

Tart cherry harvest began over the weekend, and many growers have commented they are seeing more fruit than they had anticipated as the crop ripens. Monday winds may present challenges for fruit quality, but we have not observed a lot of wind whip yet. However, we did see cherries on the ground as a result of the Monday winds, especially in orchards where ethephon was applied seven or more days ago. As harvest continues, growers continue to apply ethephon to manage the harvest of multiple blocks.

Pest report

Cherry fruit fly numbers are higher than last week with reports of 20 or more cherry fruit fly adults on yellow sticky traps in the region. Some blocks have extremely high numbers, and we are catching 80 or more cherry fruit flies per trap. Cherry fruit fly numbers are also up at the station this week with our highest catch of 10 cherry fruit flies on a trap. Growers are continuing to protect fruit from cherry fruit flies at this time and some growers who have had consistent catches of spotted wing Drosophila (SWD) are either using a material that is effective for both cherry fruit flies and SWD, or including a material specifically for SWD.

Although catches of SWD increased throughout the state in the last week, SWD numbers in the northwest remain relatively low. Last week, we found a total of 23 SWD in 71 traps in northwest Michigan. Please see the table below for more information on the locations and hosts where SWD were found.

Obliquebanded leafroller trap numbers continue to be high this week, with numbers as high as 23 moths per trap at the station. Some growers in the area with catches over the 20 or more moths per trap threshold treated for this pest prior to harvest to prevent shaking larvae into tanks. Larvae in tanks should not be a problem for growers if blocks have not had high obliquebanded leafroller catches yet this season and cherries will be harvested soon. Michigan State University Extension advises growers with high trap catches to protect against these insects as this insect is a contaminant pest (larvae in tanks) in cherries. In blocks that will not be harvested for some time and where obliquebanded leafrollers are a concern, the materials that work for cherry fruit flies are not effective against obliquebanded leafrollers. Therefore, growers with high obliquebanded leafroller trap numbers should include a Lepidopteran material for obliquebanded leafroller larvae prior to harvest. Obliquebanded leafroller larvae should be active in apples at the station at this time, but we have yet to see them.

Six apple maggot adults per trap were detected at the research station this week. Codling moth activity is ongoing, and we found three moths per trap in the station’s apple block. Since the beginning of July, evening and nighttime temperatures have oscillated around the 60 degree Fahrenheit mark when codling moth adults are typically active. As a result, determining which generation of codling moth is active in our region has been challenging. Overall codling moth populations have been low throughout the region. Second flight of spotted tentiform leafminer adults peaked this week, with 200 per trap.

As mentioned previously, conditions have been relatively dry, which is good news for fewer, recent concerns with new disease infections. Although there is some cracking in cherries, we have not observed American brown rot development. Most orchards lost a lot of leaves early in the season from cherry leaf spot infection or virus. We have also received a report of leaf loss due to possible phytotoxicity resulting from copper applications for leaf spot. We are currently investigating this issue.