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Weekly Vegetable Update 7/16/2020

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

This was a frustrating week for rain, though the reprieve from extreme heat has been nice, especially for plants that flowered this week. Forecasts around the state predicted rainfall on Monday, then pushed it back to Tuesday or Wednesday, and in many locations it never came. Inconsistent moisture at this time of year often means physiological issues like blossom end rot, but it can be hard to plan your irrigation when the weather doesn't do what we think it will. 
  • Tomatoes and peppers: We're starting to see a lot more blossom end rot this week. Maintaining soil moisture as we enter the hottest part of the season will be critical; check out our recent Great Lakes Vegetable Growers Network episode about irrigation. I also recorded a podcast this week with Dr. Inga Meadows from NC State University about spray programs in organic tomatoes; as humidity continues to be an issue, growers will have to be very proactive about disease management. I'm also seeing blossoms simply dry up and fall off due to heat. 
  • Cole crops: More reports of Alternaria leaf spot this week. We're also seeing a lot of caterpillar larvae, mostly imported cabbageworm at this point. If you're not doing so already, now is a good time to pull out your Bt sprays. Bt works more preventatively than as a rescue treatment, so make sure to use it before defoliation gets out of hand. 
  • 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. We have identified Squash Mosaic Virus near Webster MN, which is transmitted by the cucumber beetle. Powdery mildew season has begun in all cucurbits. 
  • Asparagus: as fern canopies become more dense, keep an eye out for rust and other diseases. 
  • Garlic harvest is underway. For most growers, this seems to be a good year for garlic with fairly large, healthy bulbs. Let the soil dry out as much as possible before harvest for ease of harvest and cleaner wrappers. 
  • 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. 
  • Sweet corn: the first sweetcorn is being harvested in Southern MN this week! Tip fill has been good so far. Rootworm beetles are abundant in silking corn that has not been sprayed. This week's more moderate temperatures will be helpful to corn that is pollinating now. (Sweet corn update from Charlie Rohwer, research scientist at UMN's SROC). 
Blossom end rot
Paul Bachi, University of Kentucky Research and Education Center,

Problems in the field

To remove leaves or not to remove leaves? 

This is a question I've received many times already this week. As we start to see more diseases in the field, growers want to know whether it is worth their time to remove infected leaves. The answer is, it really depends on your scale and how much time you have. Removing leaves will help to prevent pathogen spread, at least for common fungal and bacterial pathogens. Make sure you're doing so with good sanitation practices in mind; take a garbage bag with you and drop leaves directly into it, keep your hands and tools clean and sterile as you go, and only do this in dry condition with clean boots and clothes. 

Squash mosaic virus 

I reported last week that we've seen a few cases of Mosaic viruses in cucurbits, and just wanted to follow up to say that we identified Squash Mosaic Virus (SqMV) on a farm in Webster. This is important because while most mosaic viruses are transmitted by aphids, this virus is transmitted by cucumber beetles, and this has been a proflific year for cucumber beetles. . It also has secondary hosts in the Chenopodium family, so weeds like lambsquarters can harbor the virus.

More info on moisaic viruses in cucurbits
More info on tomato and tobacco mosaic virus 
Cucumber beetles transmit SqMV
Photo: NH

Insect and disease forecast


We continue to see high humidity and a high dew point, creating excellent conditions for disease spread. 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). Most growers should be implementing preventative spray programs (including organic growers) on crops that consistently have disease issues. 

Alternaria pathogens: I'm seeing Alternaria fungi everywhere this year - melons, Brassicas, tomatoes.

Powdery Mildew: once fruit set starts in cucurbits, we start to see powdery mildew. See our article about mid-season pumpkin and squash management for more info about powdery mildew.

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.

Listen to our most recent What's Killing my Kale episode about spray programs in organic tomatoes.

Aphids on peppers
Whitney Cranshaw, Colorado State University,


Squash bugs: We've been seeing squash bugs here and there for a while now, but nymphs are now emerging and developing. While we typically don't see damage until later in the season, squash bugs are much easeir to manage when they are at the nymph stage.

Aphids: Aphids have been worse this year in general, but we're seeing populations climb on farms around the state. There are many products available for aphid control, including OMRI approved products; see the Midwest Vegetable Production Guide for Commercial Growers for more information.

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 cover crops; our most recent episode was about irrigation. 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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