Article written by Madeline K. Wimmer, UMN Extension Fruit Production Educator.
Grapes
Growth update: Bud break and frost damage
Grape foliar and fruit diseases: Early-season management
Update on Mancozeb regulation (Cornell article)
General fruit information
Pest highlight: Eastern tent caterpillar
Current drought monitor map in Minnesota
UMN Extension Fruit Crop Reporting Tool
Grapes
Growth and pest management update: Bud break and frost damage
Images: When grape buds fully emerge, they are tender and sensitive to frost damage when temperatures dip below 32 °F. Photos above are Itasca at Salem Glen Winery in Rochester, Minnesota, where less than 5% of buds were damaged.
Grape buds for multiple cultivated varieties, including Itasca, have started to emerge in Southeast Minnesota (E-L chart stages 4-7). When buds emerge before the last spring frost event happens, it becomes a critical period as buds in this growth stage are very susceptible to damage. The lowest temperature yesterday morning at Salem Glen Winery in Rochester, MN, reached around 30 °F for a long enough period for visible bud damage to occur. Thankfully less than 5% of buds were damaged on cultivars that emerged, which is overall mild.
Damaged grape buds look dark green and slightly crispy compared to healthy ones. This happens because the cell membranes rupture and start to leak. If you’ve seen bud damage this year and want to share it with Extension, feel welcome to use the UMN Extension Fruit Crop reporting tool.
Grape foliar and fruit diseases: Early-season management
Bud break is the time to start preparing for early-season management for grapevine diseases. If you’re following the Midwest Fruit Pest Management Guide section on grapes, “Grape Bud Break to Prebloom” instructions start on page 138. There are a number of pathogens that can be managed at this time in order to prevent disease outbreaks later in the season. This includes pathogens that cause anthracnose, black rot, downy mildew, phomopsis, and powdery mildew.
Best practices for effective disease management programs depend on the applicator’s ability to read and follow the product label, which is the law. For many products, applications begin when shoots are 1--3 inches in growth, and products are reapplied at 7–10-day intervals, or according to label instructions. Additionally, it’s important to practice applying products in a way that avoids multiple uses of one fungicide class to prevent fungicide resistance, which is most common for downy and powdery mildew. For more information on this topic, refer to page 180 of the Midwest Fruit Pest Management Guide.
One aspect of conventional and organic pesticide product application that changes how effective sprays are is rain frequency and amount. Looking at the seven-day forecast map (May 07 - May 14) of Minnesota through NOAA’s Weather Prediction Center, most parts of Minnesota are only expected to get 0.10–0.25 inches of rain. This is less than the last two seasons where rainfall was heavier and more frequent, making it harder for products to remain on vines during this critical period.
Update on mancozeb regulation (Cornell article)
There has been recent discussion on regulations related to mancozeb, a commonly used early-season multi-site fungicide. Right now, mancozeb will remain under review with the EPA in regards to the product label regulating its use; however, it’s still important for growers to be on alert about how they might change their program if and when this changes.
Katie Gold at Cornell University published more information about this topic on their website, which includes information about current considerations and future research to look at mancozeb residue transfer and alternative fungicide programs.
Read the full article here: Update on Mancozeb in Grapes: DFR Study and Replacement Program Trials Planned for 2026
General fruit information
Pest highlight: Eastern tent caterpillar
Image: A “tent” full of young Eastern tent caterpillars in an apple tree is much easier to manage at this stage.
Eastern tent caterpillars are not a pretty sight and are an occasional pest in orchard settings. Seen here on a free-standing apple tree, these caterpillars are small enough to remove by hand without much risk of reinfestation.
When it comes to damage, young, unhealthy, and stressed trees are most at risk. For severe situations where chemical intervention is needed, spinosad, insecticidal soap, and Bt toxin— which is safer for pollinators since it is more specific—can be used for management.
Current drought monitor map in Minnesota
Image: The current drought map for Minnesota.
Some regions in Minnesota are experiencing abnormally dry and moderate drought conditions, mainly in the SW corner and north-central to parts of Northeastern Minnesota. There are signs building indicating we’re leading into El Niño conditions, which can lead to drier conditions in Minnesota and other parts of the U.S.
Preparing for drier conditions is critical for fruit growers growing crops with smaller root systems (strawberries, dwarf apple trees, blueberries), or establishing young plants. If you don’t have irrigation set up and have been considering installing a system, this might be a good year to do it. If you’re in a location where it’s not possible to install an irrigation system, having a plan to keep young plants and crops with small root systems watered is essential for critical periods without rainfall.
UMN Extension Fruit Crop Reporting Tool
Interested in sharing anything about the fruit crops on your farm? Feel free to share observations about diseases, pest management, or other production aspects using our new UMN Extension Fruit Crop Observation Report tool. If you have a question you want addressed in a future update article, you can include that in your report.
Thank you to our farm and ag professional partners for contributions to the UMN Fruit Update series. Non-credited photos in this article were either taken by Madeline Wimmer or within the UMN Extension system.
Comments
Post a Comment