Northwest Michigan fruit update – June 15, 2021

The region received some much-needed rain, but not as much as we could use; tart and sweet cherries are beginning to show some color. Strawberry harvest is in full swing.

Apple scab model output
Figure 1. Apple scab model output from the Northwest Michigan Horticulture Research Center, June 13-14, 2021.

Weather report

As of the start of this week, we have seen a quite dramatic change in weather conditions as temperatures have dropped from almost record highs last week. Since June 3, we had 11 days with daytime temperatures above 80 degrees Fahrenheit, and we hit over 90 F on Tuesday, June 8. Even the nighttime temperatures were warm and only dipped into the mid-60s. These temperatures moved the crop along, but we noticed with our trap counts, many of the insect pest numbers dropped as we may have been hitting upper thresholds for many species.

As of 14 June, we have accumulated 1,121 growing degree days (GDD) base 42 and 672 GDD base 42. Our 31-year average accumulations are 917 GDD base 42 and 502 GDD base 50. We have moved about a week ahead of normal with last week’s heat. We expect to be back near normal with the cool weather predicted for the remainder of the week.

In addition to last week’s heat, we had no rainfall. In fact, the last recorded rainfall at the Northwest Michigan Horticulture Research Center was May 29 until yesterday, June 14. It has been extremely dry, and the little rainfall that fell yesterday did not make a dent in the dry conditions. Michigan State University state climatologist Jeff Andresen estimates we lost 3-4% soil moisture last week during the hot and dry weather. He also said that about 29% of the state is a D2 level drought, and this is the highest percentage of the state in drought in many years. The Northwest Michigan Horticulture Research Center Enviroweather station recorded about 0.28 inches of rainfall on Sunday night into Monday morning (June 13 and 14).

As mentioned above, weather conditions have changed, and the weather is predicted to be cool and dry for today and tomorrow. Nighttime temperatures will also be much lower than last week, and they are forecasted to drop into the 40s and even low 30s in some areas. There is some rain in the forecast for Thursday into Friday. Then, we will be back to a cool and dry weekend. Rain is expected to move back into the state on Sunday into Monday (June 20 and 21). The 6-10 day forecast will be cooler than normal with a higher percentage of rain. However, the longer term forecast of three to four weeks is back to warmer than normal conditions.

View Andresen’s weekly weather report.

We also want to note that there was an issue with the Enviroweather system on Sunday into Monday morning, and many of the weather stations were not accurately recording rainfall. For example, on Monday morning, the Northwest Michigan Horticulture Research Center Enviroweather station recorded 0.01 inches of rain while we recorded 0.28 inches of rain when we measured manually. These data have been corrected by the Enviroweather team.

Crop report

Sweet cherries size has not moved much since last week and are about 12-15 millimeters, just a few millimeters more than the prior week. Tart cherry fruit size has not increased since last week. Apples are sizing and are 22-23 millimeters. Most fruit is the region is beyond the thinning window, and growers that did not achieve optimal thinning will have to hand thin later in the season.

Strawberry harvest began over the weekend, and northwest Michigan is harvesting strawberries at the same time as southwest Michigan. Strawberry flavor is excellent with the dry conditions although the berries might be small from the lack of rainfall. Anecdotally, strawberry sales appear to be going well as demand is high.

Pest and disease report

Diseases

Although we did not receive that amount of rainfall needed, the last wetting event did trigger an apple scab infection. The Northwest Michigan Horticulture Research Center was recorded wet for 10 hours, and it resulted in a low-level scab infection period (Figure 1). As was noted on the MSU fruit team call, both southwest and the Ridge are still catching scab spores and have not called an end to primary scab.

Please check out the RIMpro apple scab data below:

Fire blight. We have seen incidence of shoot blight in blocks across the region. The recent rainfall will be enough to move droplets of bacterial ooze around the orchard. Growers should remove any new flagging shoot and/or shoot with ooze.

At the Northwest Michigan Horticulture Research Center, we conducted a fire blight trial where we inoculated two rows of Gala to test different fire blight control treatments. Those two rows have significant amounts of blossom blight, but the adjacent rows where we used MSU plant pathologist George Sundin’s recommended strategy of 2 ounces of Apogee plus 1 ounce of Actigard, and we have almost no blossom blight infections. We initiated the Apogee/Actigard treatments at king bloom petal fall and every 10 days later for two more applications. This observation is further evidence of the importance of this combination of sprays to reduce fire blight in susceptible apple varieties.

The recent rains also resulted in a cherry leaf spot infection (Figure 2). Again, it was a low level of infection with the modest amount of rain. There is potentially more rain in the forecast, and growers should be covered for the next rain event. However, this season has been less management intensive for fungal diseases. With the predicted cool weather in the forecast, copper applications are an excellent option for this time of the season. Copper formulations have performed excellent in the efficacy trials conducted at the Northwest Michigan Horticulture Research Center.

Cherry leaf spot model output
Figure 2. Cherry leaf spot model output from the Northwest Michigan Horticulture Research Center, June 13-14, 2021.

Insects

We are still catching American plum borer this week, but numbers are down compared to weeks past. We captured an average of 2.6 moths this week. Peach tree borer numbers remain up this week; we caught an average of 13 moths this week compared to an average of 16 moths per trap last week. Growers that are targeting trunk sprays should consider this time to catch both American and peach tree borer; but again, we have caught no greater peach tree borer yet this season.

We are still catching a few oriental fruit moth this week, but numbers have remained constant for almost the duration of the season where we are catching an average of three moths per trap. Codling moth numbers are up at the Northwest Michigan Horticulture Research Center considerable this week; thus far this season, our codling moth numbers have been very low. This week, we caught 17 in one trap, nine in another trap, and none in a third trap. Most growers have set biofix for codling moth around mid-May for this pest.

The San Jose scale trap counts dropped off completely this week, and we caught no males in any of the traps. This situation was similar where we are trapping at grower sites, and we caught very few moths in commercial blocks. We hypothesize that last week’s hot and dry conditions reduced male flight activity. MSU entomologist Larry Gut also suggests that the peak male flight may be compressed this year, which will reduce the number of applications growers may use to combat San Jose scale.

Rose chafers have arrived in the region, and we have found the beetles feeding and skeletonizing leaves. Young trees are particularly vulnerable to the beetles as they can quickly defoliate the few leaves on new trees. We remind growers that the beetles have an aggregation pheromone that attract the beetles to each other; hence, the beetles tend to congregate in hot spot areas. Orchards adjacent to hay fields tend to get pressure from rose chafers after they are cut. Additionally, rose chafer management can be difficult because the beetles can re-infest an orchard quickly after a spray has knocked the population down. Most materials that growers use for rose chafers provide quick knockdown efficacy of this pest, but residuals do not last long particularly in wet weather. Furthermore, this pest can reinfest blocks quickly – we encourage growers and consultants to continue monitoring problem blocks for this pest.

We caught our first obliquebanded leafrollers at the Northwest Michigan Horticulture Research Center this week. We had only one moth in each of two of three traps, but they are starting to fly. I also had one on our screen at home the other night. Consultants have also reported that they are flying, and some have set their biofixes for late last week. Another report that consultants were seeing a high level of rolled up leaves in tarts and apples at the beginning of the season.

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