MSU Extension

Weather report                                

Summer has finally arrived in northwest Michigan. Over the last week, daytime temperatures hovered in the mid- to high 70s, and we even hit the 80s on a few days. However, overnight temperatures remain cool and most nights have been in the mid-50s. Cool overnights are predicted to continue through the week. The Fourth of July weekend is forecasted to be warm and sunny. We have accumulated 1,263 growing degree days (GDD) base 42 and 730 GDD base 50, and we have now fallen behind our 25-year GDD averages. The past week has been dry, but rain is expected today, June 30. After today, no rain is in the forecast for the remainder of the week.

Crop report

In grape vinifera blocks, the flagging of small shoots higher in the canopy is now evident. We are still expecting most shoots arising from cane tissues that were above the snow line in February and March will fade out soon. Fruit set appears to be pretty good on the low-growing shoots of vinifera vines, but the overall crop is going to be very short, perhaps 30 percent for some Chardonnay and Riesling in the best of sites; many other varieties have much smaller crop loads. It will be difficult to manage fruit so near to the ground – problems with downy mildew, powdery mildew and cluster rots are to be expected, and then animal depredation will be a problem later in the year.

Hybrid varieties also appear to have a good berry set. Some discoloration of tiny berries has been seen, but the cause and importance of this is unknown at this time. There have been reports of high rose chafer numbers at a few sites in northern Leelanau County, but the population has remained low in much of the region. Hornworm caterpillar adult moths are now flying, so small larvae may start to appear in vineyards over the next couple of weeks. Berries are in a critical stage for protection from powdery mildew, and coverage is going to be a big issue when trying to protect the fruit growing in the crowded canopy near the base of vinifera vines.

Early saskatoon varieties are starting to color up. Insect egglaying and feeding activity on fruit appears to be dropping off a bit now, but the symptoms of saskatoon juniper rust are coming on strong. Spore masses produced by this fungal disease are the most strikingly bright orange material you may ever see in nature.

Fruit continues to ripen, and cherries are starting to turn red on trees. When fruit colors up, growers are finding they have either more or less fruit than originally estimated. The tart cherry estimate from last week’s guesstimate increased to an 86 million pound crop in northwest Lower Michigan. Sweet cherries are coloring and sizing, and growers have been diligent about keeping fruit protected against American brown rot. The overall sweet cherry crop is light across the region, and brine cherry varieties are set heavier than canners.

Growers are noticing more frost rings showing up on apples from the May 20 frost event. We are still in strawberry harvest, and growers are anticipating one more week of picking berries.

Pest report

Leaf drop in cherries is widespread in older orchards throughout the region. In some orchards, there is a tremendous amount of leaf drop, and within orchards the level of leaf drop varies from tree to tree. We hypothesize this leaf drop is likely due to virus, and we have observed a similar situation in previous years with cool springs like the spring we had this season. Leaves infected with diseases, like cherry leaf spot and bacterial canker, are also contributing to some leaf drop, but to a much lesser extent than trees infected with virus. Keeping existing leaves free of diseases is crucial for ensuring that there are enough leaves present to ripen fruit and store sufficient carbohydrates to prevent tree death or decline over the winter.

In the last week, we have scouted multiple orchards for cherry leaf spot infection. While most orchards have cherry leaf spot lesions, we have observed a few orchards with high levels of cherry leaf spot infection where leaves, stems and fruit have sporulating cherry leaf spot lesions. With the exception of rain today, the forecast looks dry through the end of this holiday weekend. However, the forecast is currently calling for rain early next week, and if we do get rain early next week, growers will need to cover tissue to prevent the spread of cherry leaf spot spores. Once leaves become infected with cherry leaf spot, the numerous spores produced from a single lesion are easily spread to adjacent tissue during rain. The SDHI fungicides are the best materials available for cherry leaf spot and provide excellent control of this disease. SDHIs are also excellent against American brown rot. Growers should use caution if they are planning to use copper as phytotoxicity could be a concern in high temperatures this week.

Michigan State University Extension would like to remind growers that American brown rot is also a concern as fruit are ripening and increasing in sugar content. American brown rot will readily infect cracked fruit as well as fruit that are damaged by insects and birds. We have also observed poorly pollinated fruit that did not drop that could become infected with brown rot.

Based on the April 19 biofix, we have called an end to primary apple scab. Low levels of apple scab infections have been observed in orchards, and growers will need to keep fruit protected from this pathogen in orchards that were infected during primary as we move through the season. Growers should be aware that the pre-harvest intervals (PHI) for EBDCs tend to be long; there is a 77-day PHI for the EBDC dithane (mancozeb). Protective sprays applied prior to rain prevent scab infections and are the best way to keep this disease in check. We would like to remind growers that apple scab is resistant to the strobilurin fungicides in Michigan and as a result, strobilurins are not an effective material against apple scab in our region.

We found obliquebanded leafrollers for the second week in a row (3.33 obliquebanded leafrollers per trap) and have set biofix at June 22 at the Northwest Michigan Horticulture Research Center (NWMHRC). Last week, obliquebanded leafrollers began emerging throughout the region and thus far, populations in northwest Michigan are low this season. Pheromone-baited delta traps are highly attractive to obliquebanded leafrollers and 20 or more moths in a trap is an indication that treatment of this pest is needed.

Codling moth activity in the region has decreased in the last two weeks. We found one codling moth at the NWMHRC this week and no codling moths were found last week. We have had reports of a decline in codling moth activity last week in the region.

Greater peachtree borer activity began late last week and we found 1.33 greater peachtree borers per trap at the NWMHRC this week. Lesser peachtree borer activity is ongoing (13 lesser peachtree borers per trap) and trunk sprays targeting lesser peachtree borers and greater peachtree borers this week and last week would be well-timed for these borers.

Cherry fruit fly traps are up in orchards, and at this time we have not detected cherry fruit flies at the NWMHRC. We expect this pest will become active following rain today. The first black cherry fruit flies detected in the region were found in Leelanau and Antrim counties early last week.

We did not detect spotted wing Drosophila (SWD) in any of the 91 traps currently out in northwest Michigan last week.

Meetings and events

The Parallel 45 Vines & Wines/MSU Extension Friday meeting series continues July 10, 3-5 p.m. at Bel Lago Vineyards. Our guest speaker will be George Bird from the MSU Department of Entomology talking about the root biosphere and soil health. There is no charge for this meeting.

The seventh annual Parallel 45 Pig Roast will take place July 18 at Werner and Margaret Kuehnis’s home, 12467 Center Road, Traverse City, MI 49686. The Roast will begin at 2:30 p.m. The cost for the pig and the pig-roaster will be about $550. Portable bathrooms, glasses, plates, silverware, the pig, the keg and tables are taken care of. All attendees should bring a dish to pass and a bottle of wine. The cost will be $10 for P45 members and $15 for non-members.

The 26th Annual Viticulture Field Day and Steak Cookout will be held July 29 at the Southwest Michigan Research and Extension Center in Benton Harbor, Michigan. Informational sessions and the equipment show start at 9 a.m., and the day finishes with the ever-popular steak cook-out. Parallel 45 is working to take a group to the meeting this year, and some expenses may be covered. Contact Duke Elsner at elsner@msu.edu for more details.