Weekly vegetable update 8/25/2021

Author: Natalie Hoidal, UMN Extension educator, local foods and vegetable crops 

We're reaching the end of August, which means everyone is extremely busy harvesting. This week brought some much needed rain to growers across the state, and there is more on the way.

Crop updates 

• Cucurbits: We are in peak melon season, and I've received a couple of photos of melons with Anthracnose. A lot of farmers had issues with this pathogen last year. Its ideal conditions are humid weather and leaf wetness with temperatures in the 70s, so this week is a perfect time for it to spread if it's present on your farm. Read more about Anthracnose in cucurbits here and here. Additionally, as melons and squash start to produce fewer flowers, keep an eye on cucumber beetles. At this point in the season they can move to fruit and cause feeding damage. 

Flea beetles feeding on pumpkin fruit. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

• Tomatoes: The tomatoes I'm seeing generally look quite good this year. The common suspects like gray mold and leaf mold are showing up in high tunnels, but generally not at levels that are concerning. A few farmers have sent photos of yellow shoulder, a physiological disorder that is more likely to occur in hot, humid conditions, and also in situations where plants don't have enough potassium, or where they have too much nitrogen. It is also more common in compact or waterlogged soils. If you're seeing yellow shoulder, take note and make sure to re-assess your nutrient management program and / or irrigation program next year. In the meantime, foliar applied potassium may help fruit that is just beginning to develop. 
• Asparagus: Many growers are probably ignoring their asparagus patches right now, as there are so many other things to focus on. Take some time this week to walk through your asparagus fields and check for asparagus beetles and various diseases on the ferns. Read more about asparagus beetle and asparagus disease management in the UMN Asparagus guide.

Spotted asparagus beetle and asparagus beetle. Photo: Jeff Hahn

• Potatoes: We continue to see mostly very healthy potatoes. While it may be tempting to wash them before storage, it's generally better to do so when you remove them from storage to prevent bruising and scraping. Instead, gently brush excess dirt from the surface.
  
• Onions: Storage onion harvest and curing is underway. Some peoples' onions are smaller than usual this year, which is not unexpected given the drought. Soft rot was very common last year, and I've already received a few reports of onion diseases this year. Make sure you are curing your onions for 3-4 weeks, and not moving them into cold storage until the necks are totally dry. If possible, cool them slowly with plenty of airflow to prevent condensation as they cool. Read about proper curing and storage here. 
• Carrots: Aster yellows have been prominent in carrots this year, and a few growers have been asking at what point they should stop treating. Generally Aster leafhoppers begin to slow down with cooler weather. If you're weighing whether or not to treat, you should be scouting regularly to get a sense of your population and whether you're close to the threshold for economic damage. Regular scouting will also tell you whether your leafhopper populations are increasing, staying the same, or decreasing. In one field in Western MN, a grower I've been talking to has witnessed a steady decline of aster leafhoppers alongside a steady incline of lacewings. Regular scouting with a sweep net is the best way to make these observations accurately. Read about AY management in the Wisconsin commercial vegetable guide. 
  

 

Aster yellows symptoms in carrot (reddish foliage). Photo: Natalie Hoidal

• Garlic: Pretty much the same update as last week: make sure you're buying garlic from growers who have tested negative for Garlic Bloat Negative. Sustainable Farming Association has a directory of local garlic sellers. Continue to check bulbs for Aster Yellows and avoid saving or selling infected bulbs.
  
• Peppers: We visited a pepper field this week in Rice County with widespread virus symptoms including twisty leaves, oddly shaped fruit, and fruit with hard bumps along the skin. Any time you see a virus in your fields, it's important to identify it. Virus ID is nearly impossible to do on your own; usually it requires sending your plants to a lab such as the UMN Plant Disease Clinic for genetic testing. Why is it so important? Viruses are typically transmitted by insects like thrips and aphids, and they can have very different host ranges. Knowing where it comes from and where / whether it's likely to overwinter will help you to narrow down a management plan for future years.
• Cole crops: I've seen a couple of cases of very sad looking cauliflower and broccoli heads this week that look like they have head rot, but have tested negative for plant pathogens in the lab. In both cases, the heads were covered in flea beetles, and the feeding damage resulted in decay. While late August is typically far later than we expect to see damage, we also saw this very late season damage last year.
  
• Sweet corn: Corn earworm trap counts were above the threshold of 5 moths / trap / night in Blue Earth, Owatonna, and Rosemount. They remained low in Lamberton, and there are no other trap sites to give us information about other areas of the state. Growers who are still harvesting sweet corn. Read more about corn earworm here, and download a printable fact sheet to give to farmers market or CSA customers about wormy corn here.
  

Vegetable weather report

The entire state is projected to receive rain this week; in some cases rainfall may be excessive, with up to 5-6 inches in south central MN. Rainfall will likely be the heaviest between Thursday and Friday, and again over the weekend. Daytime temperatures should hover in the high 70's / low 80's throughout the week for most of the state, with temperatures in the low to mid 70's in northern MN.

 

7 day precipitation forecast, weather.gov

Problems in the field and things to anticipate this week

Acidifying soil in the fall

Farms that rely heavily on manure for fertility often experience a slow upward creep in pH over time, and they often accumulate salts like calcium. This is especially true in tunnels. If this is happening on your farm, fall is a great time to make amendments to your soil. Sulfur applications can bring the pH down over time to the ideal range of 6-7. 

Read more about sulfur application rates and compost recommendations for high tunnels. 

 

Why does it matter? Most vital plant nutrients have the best bioavailability at a pH range between 6 and 7. As the pH of your soil increases, your plants are less able to access the nutrients they need. Additionally, if certain nutrients build up in high enough quanitites, they may block the uptake of other important plant nutrients. 

Plant nutrient availability at various soil pH levels. Image: Wikimedia Commons

More rain = more diseases?

While this summer has been far from easy, growers have at least been able to get by with very few disease issues. Most growers still have at least 6-7 weeks left in the growing season, and while the season is predicted to stay fairly dry, there is rain and high humidity in the forecast this week across the state. If you have weekly crew meetings, this would be good week to do a recap on basic sanitation practices like starting your day in younger, healthier fields, avoiding work in wet fields, and cleaning tools and boots between tasks. This poster was developed as a training tool to explain how plant pathogens can move through vegetable farm landscapes, and how to prevent the spread of diseases. There is a printable PDF version at the end of the webpage for farmers who would like to print it and use it to train workers and volunteers.

 

Disease management teaching poster

Educational opportunities

Field day: Learn how seed saving farmers make selections to improve or maintain crop varieties, and how working with seed companies and universities can strengthen your farm operation. Topics and demonstrations will include regionally specific seed saving techniques, useful tools for both small-scale and wholesale seed growers, and more to be determined. See how regionally adapted seed varieties are bred by and for organic farmers. Hosted by Organic Seed Alliance and Greg Reynolds of Riverbend Farm, in collaboration with Koby Jeshkeit-Hagen of Seed Sages, and Dr. Julie Dawson of the University of Wisconsin-Madison.

This field day is being offered free of charge, though pre-registration is required. Please sign up at
seedalliance.org/events/midwest-regional-seeds-field-day/ Questions? Email michael@seedalliance.org, or call/txt 248-404-7616. WEDNESDAY SEPT. 1 st | 3 – 6 PM | RIVERBEND FARM | 5405 CALDER AVE SE | DELANO, MN 55328

Podcast: The Vegetable Beet: join us during your lunch break on Wednesdays for a 30 minute discussion about vegetables. Next week's topic will be about various broccoli research projects going on across the country.

Technical assistance: If you're seeing interesting things in your fields, need help identifying problems, or just want to share photos, we'd love to hear from you! Growers can reach out directly to me any time at hoida016@umn.edu, and you can submit questions and requests for diagnostic help here.