Weekly Fruit Update - 7/9/20

In this week's update:

• Hummingbirds eat SWD
• Strawberry season report
• Renovating strawberries
• Apple scab 
• Japanese beetle management recommendations
• Grape downy mildew

Hummingbirds eat SWD

I was delighted this morning to read an article from Cornell University about recent research that found that places lots of hummingbird feeders and attracting lots of hummingbirds decreased SWD raspberry infestation by 56%. It would be interesting to see how well this relationship holds up in Minnesota. Read the article starting on Page 9 of this Fruit Quarterly bulletin.

Strawberry Season Report

Irrigation was important for strawberry production this year,
as we experienced a long dry spell during fruit set. Photo: AK

Successes: 

• Huge amount of fruit harvested in a short amount of time
• Large turnout of customers
• Very little disease due to dry weather
• Overall, a profitable season for many

Challenges: 

• Dry, windy weather during bloom and fruit set reduced fruit size
• Hot weather during harvest accelerated ripening and made for hot picking
• Short season meant that things felt rushed - for many, the harvest season was around 12-14 days. 

June-bearing strawberry harvest has wrapped up in most of Minnesota, and all of the farms who have contacted me, as north as Grand Rapids, have indicated that their seasons are over. While it was a relatively short season which was brought to a close during hot, dry temperatures, I am hearing that it was also a very profitable season that drew out huge crowds for U-Pick. Rod Elmstrand of Rod's Berry Farm reports that it may have been their largest amount of berries in the shortest amount of time. 

I believe that with COVID restrictions keeping families at home, berry U-Picks offer families an outlet to leave the house that they feel is safe as it allows for easy social distancing when operated according to state guidelines. 

Kudos to all of the strawberry U-Pick farms, who did a wonderful job of ensuring customer safety, and patiently shifted farm practices to account for COVID-19. As raspberry and blueberry U-Pick farms open up this week, they can follow the examples laid by strawberry U-Picks to continue this trend of customer safety and experience.

Renovating Strawberries

When substantial amounts of weeds are growing above the height of the strawberry plants, growers should consider controlling these prior to mowing. Recommendations in article linked below. Photo: Annie Klodd.

Now that strawberry season is wrapped up, it is time for renovation. Renovation is an important process that restores the health of the plants, which directly impacts yield the following season. Read this article for a step-by-step description of renovation practices. 

Apple Scab

Apple scab leaf spots. Photo: UMN Extension.

Early season fungicide application is critical for apple scab control, from 1/4 inch green to 2-3 weeks after petal fall. Now, as leaves mature, we are seeing symptoms of scab on the leaves - this means scab was not sufficiently controlled earlier in the season. Apple scab fungi that are present now on the leaves and fruit will continue to reproduce and continue the cycle of scab infection throughout the rest of the season. 

Growers with active scab infections should continue applying fungicides (either synthetic or organic) that are rated as effective against this pathogen. Rather than relying heavily on one fungicide mode of action, rotate between fungicides with different FRAC codes, and include a broad spectrum fungicide such as Captan. More information on apple scab prevention and control, including updated fungicide options, is available here, in the Midwest Fruit Pest Management Guide, and in the Penn State Tree Fruit Production Guide. Both are PDFs available for download. The MFPMG is a free download. 

Organic fungicide options for apple scab are very limited, so early season control, destruction of overwintering spores, and use of scab-resistant varieties are especially important. Research shows that sulfur/lime sulfur and copper as the best options compared to alternatives trialed, such as neem oil, Serenade, and potassium bicarbonate. Read the labels before applying, as these products are known to cause phytotoxicity and reduce yields. Copper rates over 0.5 lb/acre may cause russeting, and not all copper products are approved for use on organic farms.

Diagnosing leaf spots on apple leaves can be very challenging! For example, frogeye leaf spot also forms brown spots and can be mistaken for apple scab (see photo of frogeye leaf spot below). Not all leaf symptoms are due to diseases - some are due to environmental events like drought or temperature fluctuation. Involving a plant pathologist via contacting Extension, and/or submitting a sample to the UMN Plant Disease Clinic, are immensely helpful in diagnosing and treating fruit diseases.

Apple leaf spots characteristic of frogeye leaf spot. Photo: AK

Japanese beetle management recommendations

Japanese beetle populations are currently thriving, and UMN trap counts show that populations in 4 locations have risen dramatically in the last two weeks. Growers must keep on top of their spray programs to manage this pest; unfortunately, cultural control methods such as hand-removal and leaving grass long are not sufficient or practical for most farms. I wrote an article with Bill Hutchison this week that compares the insecticide options available, including the pros and cons of using organic insecticides for this aggressive pest. Please continue to this article for spray recommendations.

"Killing two birds with one stone," here is a photo of both Japanese beetles and grape downy mildew. Photo: Annie Klodd 

Grape Downy Mildew

I saw a fair amount of grape downy mildew this week at two vineyards. This is earlier than I started noticing it with this frequency last year. Downy mildew is characterized by unevenly shaped yellow spots on the tops of the leaves, and white fuzz on the underside, directly under the yellow spots (see photo directly above).  

While early season sprays, which we described in depth in our May webinars, are important for managing downy mildew, the spread of populations currently present on the leaves can be minimized by including fungicides active on downy mildew in your bi-weekly cover sprays. Opening up the canopy with proper canopy management - leaf thinning, tucking, and hedging - will also reduce the humid, wet environment in the canopy that downy mildew requires. Find fungicide recommendations in the Growing Grapes in Minnesota guide, and the Midwest Fruit Pest Management Guide, both available as free downloadable PDFs.

Author: Annie Klodd, University of Minnesota Extension Educator - Fruit and Vegetable Production