Northwest Michigan fruit regional report – July 12, 2016

Managing tree fruit diseases is key following stormy weather and hail last week.

Hail damage to cherry as a result of the hail storm on July 8, 2016. Photo: Nikki Rothwell, MSU Extension

Hail damage to cherry as a result of the hail storm on July 8, 2016. Photo: Nikki Rothwell, MSU Extension

Weather and crop report

As we move into the workweek, temperatures are predicted to reach into the 90s. These temperatures are accompanied by slight chances of rain each day. After the somewhat unexpected storms that brought hail to the region last Friday, July 8, we are nervous about these high temperatures that will likely be followed by a cold front. State agricultural climatologist Jeff Andresen thought that extreme weather would be limited in the north, and extreme weather events would most likely occur Wednesday afternoon, July 13. The region is quite dry, and rain would help size the crop. However, sweet cherry harvest has begun, and there is potential for cracking if we receive too much rainfall. The Friday storms brought variable amounts of rainfall to the region: Northwest Michigan Horticulture Research Center received 0.27 inch; Bear Lake received 0.13 inch; Benzonia received 0.1 inch; East Leland received 1.34 inches; Eastport received 0.99 inch; Elk Rapids received 0.41 inch; Kewadin received 0.52 inch; Northport received 0.26 inch; and Old Mission Peninsula received 0.82 inch.

The biggest news is that we did have reports of hail in different parts of the region. The East Leland, Michigan, area was hit pretty hard, and most of the apples in this location have some kind of hail damage. The apple damage ranges from bruises and indentations to punctures into the fruit flesh. Some growers are planning to remove all apples from the tree in order to maintain tree health for next season. There are some apples that may ripen, but they will be used for juice rather than for fresh market as they were originally intended. Other areas that seem to be particularly hard hit were Central Lake and Yuba, Michigan, and along Elk Lake Road. We have grower reports of 30 minutes of hail in Central Lake, Michigan, and trees sustained considerable damage in that situation. There are varying degrees of damage in Yuba, Michigan, and along Elk Lake Road. Lake Leelanau, Michigan, area growers are also reporting substantial damage in that region.

There is also hail damage in tart and sweet cherries. For some reason, the bruising and damage to these fruits is not as obvious as it is on apples. We hypothesize that perhaps the cherry fruits were softer and the round hail “bounced” off the fruit, and when the hail hit the hard apples, the damage is more obvious. However, there are still losses to sweet and tart cherries, and some growers have already decided to not shake damaged blocks. Growers should check into diversion of damaged tart cherry blocks, as these crops could be marketable for juice. Growers should contact their insurance agent if they have crop insurance for cherries. See “Considerations for hail-damaged cherries after storms” by Michigan State University Extension for more information.

We also remind growers to assess the damage to the cherry crop closely in the coming week. Damage to cherries appeared worse yesterday, June 11, compared to the damage that first appeared after the storm on Friday afternoon. Growers need to decide if their fruit will be marketable by the time cherries would be harvested, especially tart cherries. In most cases, sweet cherry harvest is underway in northwest Michigan, and we could be weeks away from tart cherry harvest. Tart cherries are somewhat fragile in heat even in a good year, and with the predicted heat in the forecast, fruit that had hail may degrade in the coming weeks.

Growers should continue with management programs until a decision is made about harvesting the crop. If a grower decides to abandon a block, fungicide sprays should continue to control leaf spot and to keep leaves on the trees into September. Growers should also contact neighboring farms about a decision to minimize management for spotted wing Drosophila (SWD) as these populations will build quickly in unmanaged blocks and have the potential to move into orchards where harvest is intended. We are currently working on scenarios/case studies to help growers make management decisions on crop insurance and diversion. We anticipate this information will be available to growers this Friday, July 15.

If your wine grape vineyard suffered some hail damage, please report it to Duke Elsner at .(JavaScript must be enabled to view this email address) or 231-922-4822 so we can work on a damage estimate for the area. It may be advisable to apply a fungicide to protect hail-injured fruits from infection by botrytis. Our recent run of hot and humid weather favored the development of powdery mildew, and it looks like more of the same is on the horizon. We are still in the window for powdery mildew infections of the berries, so it is important to keep things covered in the vineyard. Insect activity has been very light other than a few sites where rose chafers need controls; injury by this insect is virtually finished for the year.

Most saskatoon sites are well into harvest. I have seen some injury from apple curculio and saskatoon-juniper rust at commercial sites in the Traverse City, Michigan, area, but overall the condition of the berries look great. Berry samples from an untreated block at the Northwest Michigan Horticultural Research Center show that about half of the remaining apple curculios inside fruit have now pupated, and a few have emerged from the fruits as adults. No other internal feeding insects were found this week.

Pest report

Most catches of SWD remained in the single digits and some areas caught numbers in the double digits last week. Anecdotally, orchards with higher trap catches seem to be those with many ripe or ripening alternate hosts nearby or in orchards that may not be on a rigorous SWD spray program. However, most growers have been diligent with SWD spray programs this season. Preliminary data from trials at the Northwest Michigan Horticulture Research Center indicate SWD will lay eggs into damaged cherries; hence, cherries that crack due to rain or those that were injured by hail will be suitable hosts for SWD egglaying. As a reminder, data from the research center trials has shown that excellent coverage with efficacious materials at seven-day intervals is effective for preventing SWD infestation in fruit. Wet weather is currently predicted for this week and if the area receives substantial rainfall, orchards will need to be recovered.

Cherry fruit fly activity has been reported in the region and many of the materials growers have used against SWD such as pyrethroids and Imidan should also be efficacious for cherry fruit flies. Delegate is less efficacious compared with some of these other materials and it is rated “good” for cherry fruit flies in the “2016 Fruit Management Guide.”

Obliquebanded leafroller trap numbers remain low this week in cherries at the research center with an average of four moths per trap. Most growers used a material efficacious against obliquebanded leafrollers recently or they are planning to make a pre-harvest application for this pest. We remind growers that obliquebanded leafroller numbers have been high across the state this season and most orchards will likely need to take action against obliquebanded leafrollers pre-harvest to prevent shaking larvae into tanks at harvest.

The second flight of American plum borer is underway and trap numbers for greater peachtree borers and lesser peachtree borers were higher this week than last. We found an average of 17 lesser peachtree borers per trap and an average of three greater peachtree borers per trap at the station this week.

Overall disease incidence in cherries and apples remains low. However, American brown rot is a concern at this time, particularly if cherries were injured by hail or wind. In orchards that were hit by the storm last week, most growers protected salvageable fruit from brown rot infection over the weekend. Although unharmed fruit are less susceptible to American brown rot, the coming week is predicted to be warm and possibly wet, which are good conditions for American brown rot to get a foothold, particularly if cherries crack following rain. The SDHI fungicides are excellent materials for American brown rot and cherry leaf spot at the pre-harvest timing. Indar at the increased rate of 12 fluid ounces per acre under the special label is also efficacious against American brown rot, but this material is only rated “fair” for leaf spot because we have isolates in Michigan that are less sensitive to Indar. All of the Enviro-weather stations in northwest Michigan recorded cherry leaf spot infection periods during rain late last week and some areas had an additional infection period over the weekend.

Fire blight trauma blight is a concern following high winds and damaging hail on Friday, July 8. Many growers applied either streptomycin or copper in apple orchards that were impacted by the recent storm. If trauma blight occurred, early symptoms should appear by Saturday, July 16; fire blight symptoms typically become visible 103 GDD base 55 degrees Fahrenheit after the traumatic event.

Low levels of codling moth (three moths per trap) and obliquebanded leafroller (two moths per trap) were found in apples at the research center this week.

Dr. Rothwell’s work is funded in part by MSU’s AgBioResearch.

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