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Weekly vegetable update 9/1/2021

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

September is here and the end of the growing season is in sight. We’re seeing a bit more disease pressure with the rain, but for the most part the recent rainfall has been a welcome respite. Farmers are transitioning into fall mode, seeding final successions of fall crops, and getting tunnels ready for winter production. 

Crop updates 

  • Cole crops: Disease pressure in our research plots is really starting to pick up this week. I'm getting photos of Alternaria head rot from around the state, and we're starting to see more black rot too. Review this article from last year if you're seeing increased disease pressure in your fields; it presents an overview of fall Brassica disease management strategies. Additionally, I continue to see heads of broccoli totally decimated by flea beetles. Here's a quick recap of flea beetle management strategies. At this point in the season most of these strategies are no longer viable, and insecticides should be used as a rescue option. Finally, many growers are sowing their final successions of fall Brassicas this week like arugula and radishes. Take special care to start your days in these young fields, and avoid carrying diseases over from your other Brassica fields.  
Flea beetle damage. Photo: Anna Racer

  • Cucurbits: Pumpkins are ripening ahead of schedule this year. This is really not ideal for growers with halloween markets, unless you can entice your customers with early fall decorating. Pumpkins that are left in the field too long can become susceptible to various diseases including powdery mildew and various fruit rots. Fruit can also become sunburn when the leaves start to die back from either disease or natural senescence. If you need to harvest early, make sure your pumpkins are fully cured, and store them at 50 degrees F with 50% relative humidity. Here's a great article from Michigan State about how to handle various pumpkin problems in the last few weeks before harvest.
  • Tomatoes: After last week's heavy rain I'm seeing quite a bit of splitting. If it's feasible with your labor situation, try to rogue out split fruit to avoid wasps and opportunistic diseases. At this point in the season, it's a good idea to top your indeterminate tomatoes. Topping tomatoes about 1 month before the first frost (or in a high tunnel, 1 month before you plan to pull your tomatoes) helps the plants put their energy into existing fruit. It's only recommended for indeterminate tomatoes, and only if you've pruned them to a single or double leader. If you have determinate tomatoes, their ripening physiology is very different and you won't see much of a benefit. Removing flowers results in a similar response, but is much more time consuming than simply topping the plant at the growing point.
  • Basil: Basil downy mildew is showing up in the Twin Cities. Many growers have shifted to DM resistant varieties, but if you do not have resistant varieties, keep a close eye on your basil and consider harvesting early or treating.  
Early symptoms of basil downy mildew. Photo: Meg McGrath, Cornell

  • Onions and garlic: There aren't many exciting updates in the world of onions and garlic, beyond what's already been said about curing and storage in previous weekly newsletters. Most onions and all garlic are harvested at this point - make sure the necks are totally dry before moving these crops into long-term storage to prevent disease issues. If you still haven't purchased your garlic for fall planting, now is a great time to do so!
  • Carrots and beets: Carrot and beet diseases are starting to pick up, including Alternaria (carrots) and cercospora leaf blights (carrots and beets).   
  • Peppers: Quite a few farmers harvested bumper crops of peppers this week. Generally peppers are doing quite well across the state with no major insect or disease issues. Remember to wear gloves when harvesting hot peppers - even if you don't feel it in the moment you'll feel the capsaicin under your fingernails when you try to fall asleep. I have learned this lesson the hard way more times than I care to admit.
  • Sweet corn: Corn earworm trap counts remained above the threshold of 5 moths / trap / night in Blue Earth, Owatonna, Rosemount, and Lamberton. Read more about corn earworm here, and download a printable fact sheet to give to farmers market or CSA customers about wormy corn here. Quite a bit of sweet corn has lodged (blown over / stems broken below the ear) due to the heavy rains last week following drought, coupled with strong winds. This makes harvest more challenging.
Corn earworm trap counts,

Vegetable weather report

The entire state is again projected to receive some light to moderate rain this week. Western Minnesota should see the highest rainfall amounts (~1.5-2 inches), with close to no rain in the Arrowhead region, and around 1 inch across Southern MN. Rainfall will likely be the heaviest between Friday and Saturday. Daytime temperatures should hover in the low 70's throughout the week for most of the state, with temperatures in the low to mid 60'ss in northern MN. Nighttime temperatures are dropping into the 40's and 50's, which is great for cool season fall crops, and also means more dew accumulation (which has implications for disease management). 
7 day cumulative precipitation forecast,

Problems in the field and things to anticipate this week

Determining ripeness in cucurbits: Melons, pumpkins, squash, and watermelons

A couple of weeks ago I wrote a short blurb in my weekly update about determining ripeness in melons. It was decidedly oversimplified, and so this week I decided to do a much deeper dive into harvest and storage recommendations. You can read the full article here.
Photo: Lindsey Miller

Cover crop windows are closing in

Across Minnesota, the windows for planting cover crops are quicly closing in. While there are a few crops you can plant into late Octover (winter rye, winter wheat, winter camelina), many cover crops are reaching the point in the season where they will not reliably germinate and establish before winter. If you're hoping to squeeze in a legume cover crop still this fall, some options include vetch, pea, and lentils. Use the Midwest Cover Crops Council tool to generate a planting calendar for your county, and check out our vegetable cover crop website for seeding rates and pros & cons of various cover crop options. 
Screenshot of the Midwest Cover Crop Decision Tool showing cover crop options for Dakota County MN.

Educational opportunities

Podcast: The Vegetable Beet is over for 2021. You can listen to previous episodes at, or anywhere you listen to podcasts.

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, and you can submit questions and requests for diagnostic help here

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