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Weekly vegetable update July 28, 2021

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

We've made it through another hot, humid week, and much better farming weather is on the horizon (though we still aren't getting rain). Summer crops are more consistently providing fruit this week, and the final successions of certain fall vegetables are going in the ground.

Crop updates 

  • Potatoes: This is a good time to talk about potato irrigation. Most of you are likely in either the stage between bloom and senescence, or between senescence and harvest. The 6 weeks or so following flowering are the period of development where potatoes have the greatest demand for water. Consistent irrigation during this period will result in larger potatoes, and is critical for avoiding issues like hollow heart and some common potato diseases like scab. After about 6 weeks, the vines will naturally begin to die off as the tubers mature. Slowly reduce your watering over a period of a few weeks. Read more about irrigation at different potato development stages here.
  • Carrots and beets: I've heard some reports of poor germination in carrots and beets this week. This is to be expected, as carrot germination is always tricky in dry weather. The key for carrots is very consistent moisture, especially in soils that have a tendency to form a crust. One technique I'm seeing more and more often is the use of row cover until the carrots have fully emerged, as it helps to keep the soil moisture more consistent. Otherwise just really regular irrigation should help prevent the soil from crusting over. Keep in mind that pelleted seed can actually cause more problems in dry weather. If the seed gets wet enough for the pellet to split, but then it dries out before the pellet fully dissolves, it can result in a partial splitting of the seed coating which can get in the way of germination.
  • Cucurbits: We've seen quite a few fields this week where cucurbits (especially melons and cucumbers) have died back very quickly. The cause is not always clear, and at least in some cases it is likely a combination of factors. We're not really seeing foliar disease symptoms at the farms where we've seen this. If you're seeing rapid die-back, send a sample to the disease clinic asap. The most likely causes are bacterial wilt (spread by cucumber beetles) and Fusarium crown rot. In other cases there seems to be some combination of heat stress, competition from weeds or row covers, and potential herbicide issues. If you're seeing this in your fields, please let us know! The more cases we hear about, the better sense we can develop of what's going on and how widespread these issues are.  
Fusarium crown rot, Howard F. Schwartz, Colorado State University,

Bacterial wilt, Edward Sikora, Auburn University,

  • Garlic and onions: Most of the state's garlic has been harvested. Read more about curing options on our postharvest handling page. This is another reminder to scout for onion thrips. You can read more about them in this article from our winter planning series.
  • Tomatoes: Tomatoes are generally looking great. They have for the most part benefited from the heat, and farmers all over are remarking that their tomatoes are looking larger and healthier than they've been in years. We have seen some rather bushy tomatoes that haven't been pruned as thoroughly as we typically suggest. This might be an issue logistically, simply because it may be harder to reach fruit in these plants. However, given that the rest of the summer is projected to be hot and dry, it's probably not a big deal if you haven't pruned as much as you normally would, since disease pressure is generally low this year.
  • Peppers: There's not a whole lot to report about peppers - they seem to be maturing nicely overall. We did see an aphid infestation in a tunnel this week, and this is not out of the norm considering the weather. If you have aphids in a tunnel, beneficial insects like lacewings can help to keep populations down. Products like SaferSoap of other insecticidal soaps can also help to keep populations in check.
  • Cole crops: The final succession of fall broccoli is being planted this week for growers in the southern part of the state. Flea beetles are still out, but they seem to be largely ignoring things that are not arugula and mustard. We've come across some mis-IDs this week, of growers thinking they're seeing flea beetle damage, but they're actually holes from cabbage caterpillars. If you're newer to growing Brassicas, take a few minutes to review the major insects in these crops and the damage that they do. The three caterpillars that eat these crops are active across the state, so make sure you're scouting and doing some type of treatment if they're reaching the thresholds. Treatment can be anything from physical squishing and removal on small farms to insecticides. Additionally, we're seeing some brown bead and hollow stem in our trials in Southern MN, but they are very variety-dependent. 

Brown bead symptoms in broccoli related to heat stress. Photo: Charlie Rohwer
  • Sweet corn: I don't actually spend a lot of time with sweet corn, so I asked our colleague Charlie Rohwer for an update this week. He works with sweet corn at the Southern Research and Outreach Center in Waseca. He's been seeing some (though not universal) poor tip fill and some zippering, which is likely a result of poor pollination. We've had fairly stagnant weather this summer with limited wind, which could be the culprit. 

Vegetable weather report

While many parts of the country are projected to have heavy rainstorms this week, they will again miss most of us. The very eastern part of the state is projected to get some rain, mostly tonight. However, the forecast looks dry for the next 7-10 days for most of the state. That said, it should be a bit cooler this week with daytime termperatures more consistently in the 70s and low 80s across the state. Projected dewpoints are also lower this week, dropping into the 40s and 50s later this week, so we can expect some of the humidity to clear out. 

7 day precipitation forecast,

Problems in the field and things to anticipate this week

Talking to your customers about funky vegetables

Thanks to those of you who filled out our little poll last week about whether or not you would use customer-facing resources about funky looking vegetables! Everyone who responded said "definitely" or "maybe", so here are two fact sheets we developed that you can print for your customers. They cover some of the main cosmetic issues we see in potatoes and cucurbits. Let us know if there are any other similar resources you'd like to see!

Zero interest loans for farmers suffering from drought

The Minnesota Department of Agriculture's Rural Finance Authority has declared an emergency due to drought, which makes farmers suffering from drought eligible for zero interest loans. These funds are intended to cover costs not covered by insurance, and can be used to repair or replace water systems, buy seed and fertilizer, and repair or replace farm buildings. Read more about it here.

Educational opportunities

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 new crops being grown in the Midwest.

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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