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Weekly Vegetable Update 7/7/2021

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

We are entering a new phase of the season where warmer season crops are starting to mature. It's also the part of the season where growers are doing everything at once - planting, harvesting, tending and weeding - and farming can start to feel extra exhausting. While most growers did not get a full inch of rain this week, many people got at least a bit, which feels like a lot after so many weeks of no rain at all. We have a very pleasant week ahead of us weather-wise, just in time for a busy week of planting and weeding.

Crop updates

  • Cucurbits: Field grown cucumbers are starting to mature and will be in full production mode in the next few days. Winter squash are starting to form on the vines. Start scouting for powdery mildew on a regular basis, as preventative treatments are much more effective, and this is the time of year we start to see symptoms.
Fruit set in melons and winter squash. Photo: Natalie Hoidal
  • Cole crops: Many growers have their major push for planting fall brassicas right about now. If recent years have taught us anything about flea beetles, it's that we shouldn't expect that they will disappear in June. I now recommend that folks should consider planting a trap crop of arugula or mustard with each new Brassica planting. Spring head-forming brassicas are maturing more reliably now for markets, and we're seeing typical symptoms that we would expect during a hot year including bolting and loose heads. I've also had some reports of radishes splitting at harvest. This is caused by a few things: leaving radishes in the ground too long, heavy rainfall followed by drought stress, and too much nitrogen. Variety selection can also make a big difference.

Loose broccoli head. Photo Natalie Hoidal
  • Potatoes: Potatoes are flowering across the state, and some people are already harvesting very early potatoes. For most growers, this period between flowering and harvest is the most important for healthy tuber formation, so now is the time to really focus on potato irrigation. I've also noticed a lot of Japanese beetles on potatoes this year, but they do not seem to be causing significant damage.
    Aster leafhopper populations seem to be dropping in scouting done in wheat fields in Southern MN, but it may still be a good idea to opt for Aster Yellows resistant varieties for your fall successions (see last week's update for a list).

  • Beets:  Despite the relatively dry weather, sugarbeet growers are starting to spray for Cercospora leaf spot. Table beet growers should do some scouting and keep an eye on populations. Learn more about Cercospora leaf spot here (will download as PDF). 
  • Peas and beans: Most early pea plantings have been petering out, but it seems like the rain we've had in the past two weeks has encouraged a final growth spurt for some pea plants. Dry beans are flowering, and climbing varieties will require some dedicated trellising attention over the next couple of weeks. Continue to scout for insects, particularly aphids, which can transmit viruses.
Dry beans are flowering. Photo: Natalie Hoidal
  • Tomatoes: The very first field grown tomatoes are coming in, and high tunnel tomatoes are coming into their period of full production. We tend to see a lot of blossom end rot in the first flush of tomatoes. Remove any tomatoes with BER symptoms as soon as you see them, as they will not grow out of it to form marketable fruits. 
  • Garlic and onions: We are in the final stretch, with a couple of weeks until harvest. I've seen a few people harvesting early, and generally reporting high yields. Keep irrigating your garlic, as you're now in the most critical period for healthy bulb formation, and keep scouting for aster yellows symptoms. I received a few reports of very high populations of onion thrips this week. Here's a great how-to video about scouting for onion thrips.
  • Sweet corn: I've anecdotally noticed that in a few locations, the earliest transplanted successions of sweet corn are not doing well. The plants are shorter than the later planted successions, and are silking when the plants are still quite small. There's not much you can do in this situation, other than rely on your later successions, and consider planting a bit later next year if you're having problems. Our crops IPM specialist is starting to detect corn rootworms in Southern MN and anticipates that this may be a difficult year. Read more here about scouting for corn rootworm. This is a sporadic pest that can vary significantly from field to field. Keep in mind that you are likely seeing some adults in the silks (see photo below for reference), but the adults do not damage your crop. Rather, they lay their eggs in the soil at the base of your corn plants, and they emerge next year. As long as you're rotating your sweet corn plantings, you can avoid damage. More info about corn rootworm in sweet corn here.

    Western corn rootworm adults. Photo: Natalie Hoidal

Vegetable weather report

Temperatures are finally cooling down for the week, with highs in the low 80'sacross the state (maybe high 80's early next week in some places), and nighttime lows dropping into the 50's. Northern Minnesota is not expected to get much rain in the upcoming week, with projections around 0.1 - 0.25 inches. Southern Minnesota can expect more like .75 - 1.23 inches, and the metro should fall somewhere in between.

7 day precipitation forecast,

Problems in the field and things to anticipate this week

Applying herbicides at this point in the season

I realize that most of our readers are organic and do not use herbicides. But, I've received enough questions about using herbicides at this point in the season that I'd like to address some best practices here. 
  1. The wrong herbicide, or even the right herbicide applied in the wrong way, can damage your crops and have implications for human health. Use the Great Lakes Vegetable Production Guide to help you choose the right herbicide for your crop. If the crop you're hoping to spray is not listed on the label, it is illegal to spray that particular herbicide. 
  2. Most vegetables are broadleaf plants. The easiest herbicides to apply to broadleaves are herbicides designed to kill grasses. If you need to apply a broadleaf herbicide (to kill broadleaf weeds) in your vegetable fields, consider investing in a shield that can be placed over the nozzles on your sprayer to minimize drift and keep the spray pattern as much as possible between rows. 
  3. Spray when conditions are calm, with 3-10mph winds. 
  4. When conditions are hot and dry, herbicides are more likely to cause damage to crops. Avoid spraying when temperatures exceed 85 degrees F. 
  5. Dry soils are easier to cultivate - consider cultivating as an alternative to herbicides, especially on high value crops if you're worried about drift.
  6. Read the labels carefully. Pay particular attention to the Re-entry interval (the amount of time you need to wait between an application and re-entering the field safely), and the pre-harvest interval (the amount of time you need to wait between an application and harvest).

Get ready for sweet corn harvest and birds

Birds tent to make their way into sweet corn fields a few days before harvest, which is exceedingly frustrating. As sweet corn nears maturity, consider making a plan for preventing birds in your fields. This plan should be diverse, with multiple tactics, and rotating tactics since birds learn and adapt quickly. Tactics can include visual, audio, and olfactory or chemical repellents. Learn more about methods for repelling birds in sweet corn. 

Photo: Gaimard, Pixabay

Educational opportunities

Field day! we'll be hosting a field day next Tuesday evening about organic management strategies for beginning vegetable farmers at Shepherd Moon Farm and Big River Farms. We'll showcase field trials related to Colorado Potato Beetle management, summer cover crops, nutrient management trials, and discuss disease management. Join us if you can - we'll have food, Spanish and Hmong interpretation, and mileage reimbursements. Register and learn more at

Photos: Natalie Hoidal, Jeff Hahn, UMN Extension.

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 garlic.

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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