Weekly vegetable update 9/1/22

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

Summer is officially over! Early September is one of the most exciting times of year on vegetable farms. Pretty much everything is ready to harvest and CSA boxes and farmers market stands are full with a diverse array of crops. We have a few days of very hot weather still ahead of us, but temperatures have become generally more manageable. This update includes: a review of issues from the field this week, some guidance about winter greens, and some strategies for disease management. 

Problems in the field / things to note this week

Soil compaction

The impacts of soil compaction on yields can be hard to measure, but sometimes we have opportunities to see it clearly. The photo below is from a field where peppers were planted in last year’s field row. The peppers from the field row are smaller and more yellow than the peppers planted on either side. 

Photo: Natalie Hoidal

Plan accordingly if planting winter greens

As winter greens in unheated tunnels become more popular, keep in mind that most of the media we can access (e.g. podcasts, YouTube videos, etc.) comes from farms a bit further south and in warmer growing zones than ours. It is absolutely possible to grow winter greens successfully in Minnesota, just make sure you have realistic expectations and that you're planting the right crops. The persephone period, the period where day lengths are less than 10 days and plant growth slows down substantially, happens pretty early in Minnesota. In Northern Minnesota, this period begins around November 1, and in Southern Minnesota it happens around November 8th. This means that across Minnesota, it's too late to plant kale as a winter crop, but farmers in southern MN can still plant spinach in the next week or so. For growers further north, baby spinach and baby leaf Brassicas are the only reliable option if you haven't planted already.

Soil treatments for soil diseases

Do you struggle with persistent soilborne diseases in your high tunnel or in your fields? There are two soil treatments that growers may be interested in trying: biofumigation and anaerobic disinfestation. Biofumigation is commonly used in fields infected with phytophthora, and anaerobic disinfestation is more commonly used in high tunnels. If you're curious about these methods and how they might fit into your farm management toolkit, check out our recent podcast episodes where we explore both the efficacy and the nuts and bolts of these treatments. You can stream episodes directly from https://www.glveg.net/listen or look up "The Vegetable Beet" on Apple Podcasts, Spotify, or anywhere else you stream podcasts.  

 

Crop updates

• Cucurbits: Winter squash are coming in more reliably this week. While many winter squash varieties are sold directly from the field and thus storage is not a consideration, proper curing is still important to extend the shelf life when they reach your customers. For much of the state, the week ahead will be warm and rainless, which is ideal for field curing. Squash are considered cured when you can no longer puncture the skin with your finger nail. In general, cucurbits are looking great across the state. Many growers will get away with not having to manage for powdery mildew at all this year. As cucumber vines age, I am getting more reports of spider mites. At this point in the season if your cucumbers have slowed down substantially, it may be a better option to terminate your plants than to spray again for mites. However, if you're seeing high spider mite pressure now, make sure to make note of it and come up with a plan for next year, which may include insecticides and / or predatory mites.

 

Spider mites on cucumber leaves. Photo: Natalie Hummel, Louisiana State University AgCenter, Bugwood.org

• Garlic: As you prepare to plant garlic, check for bulb mites (see last week's article), and any other issues like aster yellows infected cloves. If you still need seed, check out the Sustainable Farming Association's Premium Garlic Directory. All growers selling through this directory have tested their garlic for garlic bloat nematode.
  

• Cole crops: Fall harvests of Brassicas like broccoli, cabbage, cauliflower, turnips, and radishes have started to ramp up again. The cooler nights we've been experiencing are perfect for triggering head formation in head forming Brassicas, but the dewy mornings are also ideal for disease spreading conditions. We're seeing more bacterial stem blight in broccoli this year than we have in the past. If you're seeing this on your farm (see photo below for reference), feel free to reach out to me and I can get it analyzed in the clinic. We're interested in learning more about which specific pathogens are causing this issue.

• Tomatoes: I started to see more yellow shoulder symptoms this week compared to the levels I've been noticing throughout the summer. Yellow shoulder is quite complicated with many interacting stressors that can cause it, including waterlogging, too much nitrogen, not enough potassium, and other environmental stressors. I saw a particularly bad case of yellow shoulder symptoms in a field where the grower accidentally left the irrigation running for 24 hours about a week before; this may or may not have been related. Additionally, I'm noticing more opportunistic insects in split or otherwise damaged fruit. Every year I get a question or two about whether insects like picnic beetles or bumble flower beetles are damaging tomatoes; usually they simply show up to feed on the juices once the damage has already been done. Once they enter a field, their populations seem to increase rapidly.
  

• Sweet corn: Corn earworm trap counts have not been updated this week yet, but check back over the weekend if you're interested and continue to scout your own fields for corn earworm. 
  

Connect with the fruit & vegetable team

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 diagnostic help below.