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Weekly Vegetable Update 7/9/2020

Author: Natalie Hoidal, UMN Extension Educator, Local Foods and Vegetable Production

If you're seeing interesting things in your fields, insects and diseases, or just want to share photos, we'd love to hear from you! As always, don't hesitate to reach out with questions and pictures. We're still here for technical assistance over the phone, via text, or via email.

Vegetable questions go to me (Natalie):
Fruit questions go to Annie:
Food safety questions go to Annalisa:

Crop report

  • Tomatoes and peppers are setting fruit, both in the field and high tunnel. Some growers are already starting to harvest cherry tomatoes. We've seen all of the standard tomato diseases - keep scouting regularly. For fungal pathogens, pruning out diseased tissue when conditions are dry (and regularly sanitizing your clippers) can help to prevent disease spread, as can preventative fungicide applications. *Next week I will be recording a podcast with a tomato disease specialist from North Carolina - feel free to email me questions ahead of time!
  • Cole crops: Alternaria season is officially upon us. I've received reports of Alternaria in brassicas from a few growers now (still no black rot though!). Keep scouting for caterpillar larvae, as we're still seeing plenty of eggs. 
  • Cucurbits: cucumber and zucchini production are in full swing. Harvest as regularly as possible to prevent soft rots, which can easily develop on fruit that sit for too long. Anticipate some blossom end rot as well, and keep the soil moisture as consistent as possible. Cucumber beetles are still active. 
  • Asparagus has reached the fern stage for most growers at this point. Keep an eye out for rust and asparagus beetles on the stalks. 
  • Garlic is in the bulb forming stage, and many farmers have begun to harvest. Harvesting when the soil is dry will help the bulbs come out clean. 
  • Potatoes: some farms have started to harvest early potatoes; others will wait a few weeks to even a couple more months to harvest. We've seen some wind damaged leaves in a few potato fields that looked a little like disease lesions, but haven't seen any actual diseases so far. Insects remain problematic. 
Cucumber beetles and pollination challenges
Photo: NH

Problems in the field


I've seen a couple of reports of viruses in cucurbits. These are most likely cucumber moisaic virus, but we'll have an official diagnosis soon. With viruses, it's important to focus on both the source of the virus and the source of transmission. Cucumber moisaic virus is mostly transported by aphids, so growers seeing virus symptoms should:

1. Remove all plants showing virus symptoms from the field
2. Manage aphids

Plants infected with mosaic viruses typically have unmarketable fruit, so removing infected plants as soon as possible is the best practice. Once present, viruses can also spread on your clothes, hands, and tools, so tread carefully through virus infected fields, change your clothes afterwards, and sanitize your hands and tools as you go.

More info on moisaic viruses in cucurbits
More info on tomato and tobacco mosaic virus

Viral symptoms in Zucchini
Photo: Waxwing Farm

Heat stress

Heat can cause flowering and pollination issues in a variety of crops. Cucurbits are the most famous for this. There's not actually a distinct temperature at which pollination stops or at which flowers or fruit abort; rather, hotter temperatures cause the plants to shift their balance of male and female flowers. In some varieties, they stop producing female flowers when it gets too hot. Usually there's more of a gradual shift and imbalance vs. completely stopping female flower production. High enough temperatures (90 d / 70 n) temperatures can result in female flower abortion, BUT high light levels also help to mitigate this. Thus, if you've left ample spacing between plants, you face less risk of fruit and flower abortion.

Heat stress can also cause flower abortion in peppers and tomatoes. Heat stress also impacts YOU - take breaks and drink plenty of water. Heat stress is common, especially in these busy weeks where you're planting, maintaining, and harvesting all at once.

Soil crusting in direct seeded crops

Many growers are direct seeding carrots, beets, and other crops this week. We're seeing heavy rainfall followed by hot weather, which is perfect conditions for soil crusting. See our recent article about preventing soil crusting.

Insect and disease forecast


This week has been extremely humid, and we can expect more humidity in the forecast. Scout regularly, send samples to the disease clinic for identification, and removed diseased tissue if possible (only when conditions are relatively dry and your hands / tools are clean). Keep an eye out for Alternaria in brassicas, powdery and downy mildew in cucurbits, aster yellows in carrots, early blight, Fusarium, and Septoria in tomatoes, and in general for plants that look not quite right. A few things to be particularly aware of: 

Alternaria leaf spot in Brassicas: this disease has become increasingly difficult for MN growers, particularly those just South and West of the Twin Cities. This study from Cornell shows that while many OMRI approved products are ineffective, straw mulch may substantially reduce Alternaria problems. There are many conventional fungicides recommended for this fungal disease.

Powdery Mildew: once fruit set starts in cucurbits, we start to see powdery mildew. Monitor closely from here on out. More info on organic management of powdery mildew, and more info about managing it with conventional fungicides. 

Late blight spores have been detected in traps near Detroit Lakes. So far there are no reports of late blight in potato or tomato fields.

Look out for downy and powdery mildew
David B. Langston, University of Georgia,


Not a lot of new information here. We continue to see high populations of cucumber beetles, potato beetles, potato leafhoppers, cabbage caterpillars, fourlined plant bugs, some tarnished plant bugs, and aphids. See reports from the last couple of weeks for more information on these insects.

Educational opportunities: things to listen to in the field

Great Lakes Vegetable Producers Network
join us during your lunch break on Wednesdays for a 30 minute discussion about vegetables. All previous episodes can be downloaded as podcasts, and are available on Apple Podcasts. Next week's episode will be about biostimulants. You can also visit the network page for recordings of all previous episodes, and listen along to the mp3 recordings while you work.

Also remember that What's Killing my Kale is ongoing, with recent episodes about flowering and fruit set in cucurbits, apple crop load management, measuring soil health, nutrient management in wet soils, Spotted Wing Drosophila updates, and climate change adaptation. These episodes are also available through the Apple Podcasts app, or can be downloaded directly online.

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