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Weekly Fruit Report, 6/18/2020

Nova summer-bearing raspberries are showing nice fruit set. Photo: Annie Klodd

Author: Annie Klodd, UMN Extension Educator, Fruit and Vegetable Production

If you're seeing interesting things in your fields, insects and diseases, or just want to share photos, we'd love to hear from you! As always, don't hesitate to reach out with questions and pictures. We're still here for technical assistance over the phone, via text, or via email.

Fruit questions go to Annie:
Vegetable questions go to Natalie:
Food safety questions go to Annalisa:

In this article:

  • Strawberry U-Picks opening with COVID guidelines
  • Dry weather reducing disease pressure, plant water status
  • Investigating Undiagnosed Berry Symptoms
  • Strawberry leaf diseases on stems and fruit
  • Herbicide drift damage continues
Strawberry season has begun in Minnesota! Photo: Annie Klodd

Strawberry U-Picks opening with COVID guidelines in place

Multiple strawberry farms opened for U-Pick this week in southeast Minnesota, the metro area, and west central Minnesota. These farms are doing a great job of keeping their customers informed about changes they will see at the farm, as we all work together to comply with COVID restrictions. From introducing guidelines to the tune of "A Night Before Christmas" to posting beautiful photos to accompany the guidelines, Minnesota farms are finding clear and customer-friendly ways to encourage customers to safely visit the farm. We appreciate the extra effort that these businesses are taking. 

Per the recent executive order by Governor Walz' office, all farms and farmers markets in Minnesota (not just fruit and vegetable farms) must have a written COVID preparedness plan. Please see this article by Annalisa Hultberg for more information about what is required by the state and resources to help make this process easier.

Dry Weather Reducing Disease Pressure, Plant Water Status

Not only has our weather been dry lately in most of Minnesota, it has also been windy and hot. The good news is that most fruit diseases do not spread well under these conditions. Diseases like botrytis fruit rot, anthracnose, downy mildew and many others require wet, humid weather to reproduce and spread on the plants. Hopefully, this is leading to reduced disease pressure for diseases that are very active at this point in the season. 

The potential downside of hot, dry, windy weather is that it can cause drought stress on fruit crops. In order for our crops to photosynthesize, they open their stomata (pores) during the day to absorb sunlight. This process also causes water to evaporate out of the stomata (evapotranspiration). During windy, dry, hot weather, more water is exiting the plant, and the plant may essentially have trouble keeping up. Potential symptoms of drought stress include leaf drying, reduced plant growth, wilting, reduced fruit size, and slower ripening.

Investigating Undiagnosed Berry Symptoms

We are currently working with researchers in Minnesota and other states to determine whether some unknown symptoms we are seeing on blueberry and aronia plants are due to the hot, dry weather, or whether they are caused by something else like diseases or nutrient issues. If you have seen symptoms like either of the below photos, please let us know - it will help us investigate the issues.
Aronia fruit turning yellow and falling off the plants. The cause is being investigated. Photo: Shane Bugeja.
Blueberry leaves with browning and drying that starts on the leaf margins, with some blotches starting on the interior as well. The cause is being investigated, but may be due to dry, hot weather, nutrient issues, or a disease. Photo: Jim Luby

Strawberry leaf diseases on stems and fruit

Symptoms of leaf scorch on strawberry leaves, seen on 6/15/2020. Photo: Annie Klodd

Strawberry stems that have symptoms of leaf spot or leaf blight, both leaf disease that can also girdle stems. Photo: Annie Klodd, 6/15/2020.

Despite these recent dry days, growers should still remain vigilant about diseases that have been active for the last few weeks, which started to spread in late May and early June when we had more frequent rainfall mixed with hot weather. If effective sprays were not applied at the right timing during that wetter period, strawberry leaf spot diseases would have started spreading and are still present on the plants.

On my weekly scouting trip on Monday, I found disease symptoms on the stems of strawberry plants that Dr. Jim Luby believes to have spread from the leaves. 

Once leaf diseases spread to the stems, blossoms, and fruit, they cause more damage than they do on the leaves. Diseases on the stems can girdle them, preventing adequate water and nutrient transport to the fruit. When this occurs, the fruit may be small, deformed, or dry up before ripening.

As we anticipate a much-needed rain today or this weekend, growers should be keeping up with their spray programs and applying effective organic or synthetic fungicides to prevent the spread of berry diseases.

Herbicide drift damage continues

Dicamba drift damage causing twisting and wilting on raspberry leaves. Photo: OMAFRA.

Natalie and I continue to receive inquires from growers about herbicide drift symptoms on fruit and vegetable crops this week. From a conversation with Thom Peterson, Minnesota Commissioner of Agriculture, earlier this week it seems that many cases of drift on specialty crop farms are never reported to Minnesota Department of Agriculture.

If you suspect that your crop has experienced herbicide drift, the Minnesota Department of Agriculture urges you to file an investigation form on their website so that they can investigate the source of the drift. Without a report, the MDA is unable to assist in finding the source of the drift or hold the party accountable. According to MDA staff, drift investigations for fresh market crops are expedited due to the high value of the crops, and the need to bring them to market throughout the season.

As Extension Educators who also have personal farming backgrounds, we understand that drift is a challenging and frustrating issue that can devastate crop production on high value specialty crop farms. We also understand that many factors go into the decision to report suspected herbicide drift. More information about the reporting process is available here or by visiting MDA's Pesticide Drift Complaint Process and Timeline page. Natalie and I are always available to discuss this process as well.

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