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Weather report

The weather has been more than unpredictable over the past week. We have seen some record-breaking rainfall events, and the daytime temperatures are predicted to be in the 90s for many days this week. In addition to the wild weather in general, the differences between short distances have been remarkable. Marked amounts of rainfall have been reported less than 10 miles apart, causing some growers to question Enviroweather. Growers can be assured that the Michigan State University weather system is working well, and we are seeing tremendous variability in rainfall amounts in close proximity. The radar has been showing small bands of active weather coming across Lake Michigan, and as a result, there are big differences in rainfall totals across the region. These excessive rainfall events have also been coupled with high winds. Wind gusts were reported near Central Lake at 63 mph. Surprisingly, we have had no hail reports from the region, but hail does seem likely with these extreme conditions.

On Monday, June 29, the Northport Enviroweather station recorded 6.33 inches of rain; this rain fell from 8:25–10:55 a.m., less than an hour and a half. According to NOAA’s Atlas 14 and Jeff Andresen, MSU agricultural meteorologist, a system that predicts the statistical likelihood of rainfall events put a 1,000-year event at 5.42 inches of rain. In addition to the amount of rain, there was a 5-minute period where 0.75 inches of rain was recorded on the Enviroweather station—more than Andresen has ever seen recorded in a 5-minute period. Antrim County also saw intense rainfall and over 4 inches of rain fell in a short amount of time also on June 29. There were flood warnings on Monday, June 29, and after the rains, roads in Leelanau and Antrim counties have been damaged by the excess water.

In addition to the rainfall, we have had extreme heat across northwest Michigan. We are not alone as the whole state is under a heat advisory. The bottom half of the state is under an extreme heat warning, which is a classification given when temperatures can reach over 110 degrees Fahrenheit. The daytime high at the Northwest Michigan Horticulture Research Center on June 30 was 89.4 F. Extreme heat is predicted through July 2, and then more normal July weather comes in over the weekend, although conditions will still be warm.

Be cautious when working in high temperatures. Take breaks, drink lots of water, and keep an eye out for workers that are showing symptoms of heat stress. “Heat stress prevention among farmers heading into Michigan’s summer” is a good article from Michigan State University Extension about heat stress prevention.

At the Northwest Michigan Horticulture Research Center, we have accumulated 1282.2 growing degree days (GDD) base 42 and 620.8 GDD base 50. Our 36-year averages are as follows: 112 6DD base 42 and 733 GDD base 50. These accumulations are similar to our long-term averages, which are 1282 GDD base 42 and 773.7 GDD base 50.

Crop report

Tart and sweet cherries are coloring, and some growers started ethrel applications late over the weekend and into early this week. Our sweet cherries are ripening, and Black Pearl at the Northwest Michigan Horticulture Research Center are tasting good. We are planning to harvest that light crop later next week. There is some variability in ripening in sweet cherries, perhaps from the cool spring and length of bloom in sweets. Montmorency tart cherries are at 17  mm. Balaton fruit is at 6 mm. Growers in southwest Michigan have wrapped up harvest, although the crop was extremely light. Growers are harvesting sweet cherries in west central Michigan and anticipate shaking tart cherries over the coming weekend.

Apples at the Northwest Michigan Horticulture Research Center are growing quickly. Last week, our Galas were at 26 mm and this week they’re measuring 33 mm. Honeycrisp was at 28 mm last week and 33 mm this week. The thinning window is closed for most growers in the region. Our thinning appeared to work adequately at the station. We continue to see some blocks that have considerable size differentials in the clusters where there are 10-15 mm differences between king fruit and some of the lateral fruit. Even with the huge gap in size, the small fruit still are not dropping off, nor do they seem that they will drop off in the future.

Disease report

Apple scab. We have called the end to primary scab in northern Michigan. In fact, all of Michigan has called the end to primary scab season.

Cherry leaf spot. Unlike scab, there is no primary season for leaf spot, and growers will need to protect new tissue from this fungus throughout the growing season. We want to delay infection as long as we can because early leaf spot infections can lead to early defoliation, and we need all the leaves to ripen the valuable crop this season. Captan is an excellent leaf spot material. Flint and Cevya are also rated good to excellent. Coppers are also excellent against leaf spot, but should be applied in hot temperatures as these materials may cause phytotoxicity.

American brown rot. This is the fungal disease we are more concerned about now. Sweet cherries are ripening, and the sugar content in the fruit is increasing. This fungal pathogen thrives on ripening sweet cherries, and with the rain and high humidity, brown rot needs to be controlled.

American brown rot is a disease that grows best and fastest in moderately warm conditions—it takes much longer to grow when it is cold (Table 1). In extreme heat, temperatures above 85 to 90 F, combined with dry weather, strongly inhibit fungal growth and infection. We have had those hot temperatures, but we have also had high humidity and various amounts of rainfall. These conditions are still concerning, and growers need to be protecting ripening sweet cherries against American brown rot.

We have materials that are rated excellent against brown rot, but most of them are SDHI fungicides. Use materials as judiciously as possible as we have no new American brown rot materials in the pipeline. However, fruit still needs to be protected, and growers may have to tighten up spray intervals if these humid conditions continue. The temperatures are predicted to drop after Thursday, July 2, so those daytime highs are more conducive for the American brown rot pathogen growth compared to over 85 F.

Use the maximum rates of all fungicides: Merivon (6.7 fl oz/A), Miravis (5.1 fl oz), Tesaris (5.6 fl oz) and Cevya (5 fl oz). Resistance management is extremely important, and these materials need to be tank-mixed with a broad-spectrum fungicide, such as Captan or sulfur.

In addition to the warm and wet weather, rains will likely cause cracking in sweet cherries. Cracks are another opportunity for American brown rot to infect cherries, and with more cracking, we see more brown rot infection.

Lastly, to add insult to injury, the birds are out in sweet cherry orchards. Bird pecks are another way for these opportunistic fungi to cause infection. Growers will need to be on the American brown rot management game with all of these challenges.

Table 1. Temperatures and minimum hours of wetness required to cause American brown rot infection.

Insect report

Codling moth. We are at peak egg laying for first generation codling moth at the Northwest Michigan Horticulture Research Center. Growers will need to manage larvae as they hatch.

Plum curculio. We have heard reports of new stings in cherry. These warm overnight conditions are likely causing plum curculio activity to remain high. These weevils prefer warm evening temperatures, and they are particularly active when humidity and moisture levels are high. These current conditions are perfect for plum curculio, and in most seasons, we start to see activity decline at this point in the season, but after a slow start and cold spring, plum curculio are still actively laying eggs in orchards.

Obliquebanded leafroller. We have had many reports of larvae in apple and cherry orchards. Obliquebanded leafroller is a threat to apples as a direct pest; the larvae feed on leaves and fruit in summer and fruit in fall. In cherries, obliquebanded leafroller does not feed on fruit, but they can cause damage to cherry leaves, which can result in defoliation. The greater concern of obliquebanded leafroller in cherries is the threat as a contamination pest, as they can be found in cherry tanks if present in trees at harvest.

Growers with past obliquebanded leafroller issues need to be on the lookout for small, newly hatched obliquebanded leafroller larvae. We are catching a few moths in traps, and these moths are mating and laying eggs. The larvae will be present during cherry harvest and have the potential to be shaken out of the trees during harvest and wind up in cherry tanks.

Spotted wing drosophila. Important news! We have found spotted wing drosophila larvae infesting Sams at the Northwest Michigan Horticulture Research Center. We have also heard reports of spotted wing drosophila-infested Cavaliers in the region. In most years, we have seen limited sweet cherries that have been infested with spotted wing drosophila. However, this year, we have seen increased infestation in sweet cherries.

Ripening sweet cherries need to be actively protected against spotted wing drosophila. These are sneaky insects, and a tight insecticide program needs to be maintained to keep larvae out of fruit. Additionally, the spotted wing drosophila model on Enviroweather is indicating we’re at moderate risk for spotted wing drosophila infestation in tart cherry. Initiate spotted wing drosophila programs in tart cherry as soon as possible.

We have lots of insecticides that are rated excellent for spotted wing drosophila in sweet and tart cherry: Exeril, Apta (good to excellent), Verdepryn, Entrust, Warrior and Mustang Max. Imidan is not labeled in sweet cherry but can be used in tart cherry; this insecticide is an excellent material against plum curculio.

Again, spotted wing drosophila thrives in warm and humid conditions. However, extreme heat will reduce activity: the next two days may slow spotted wing drosophila activity, but by the weekend the daytime highs will be in the 80s and conducive for activity. High humidity also favors spotted wing drosophila population growth, and this pest can have one generation in less than seven days under optimal conditions. Growers need to be activity managing spotted wing drosophila now.

This work is supported by the Crop Protection and Pest Management Program (grant no 2024-70006-43569) from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.