Weekly Vegetable Update July 23, 2026

Authors: Natalie Hoidal & Marissa Schuh

Last week was brutal. Extreme heat and extremely poor air quality during one of the busiest weeks of the year means that this week, farmers are in major catch-up mode: hand pulling weeds that got away, harvesting garlic, planting final successions of fall crops, and just generally keeping things running. These last few days have provided some amazing relief, and while there will likely be more wildfire smoke ahead, NOAA is actually predicting fairly “normal” heat and precipitation conditions for the rest of the summer.  Much of the state is somewhere on the drought spectrum. 

Many vegetables have shallow roots

We’ve had a couple of calls this week where we are reminded just how shallow many of the roots of our vegetable crops are.  When thinking about things like weeding, irrigation, or even the collars we use to deter cutworms, remember that many vegetables, especially our transplanted ones, root shallowly in the soil. 

One common assumption we have is that tomato and cucumber plants produce a deep taproot, and this is generally true when they are direct seeded. However, these plants are actually very unlikely to produce a taproot when transplanted, instead relying on a sprawling network of roots near the surface. Here’s a pretty cool set of photos comparing tomato roots grown from seeds vs. transplants from one of our favorite books, Root development of vegetable crops, published in 1927! Yes, working in Extension skews your favorite books in interesting ways…

A comparison of the root systems of a transplanted and direct seeded tomato. Image: Root development of vegetable crops by John Weaver and William Bruner.

Farming in smoke: a marathon

While we’re getting a few days of respite from the smoke, fire fighters are telling us that fire season has just begun in Minnesota. We’ve probably all had the miserable experience of working outside in 90 degree heat while wearing an N95 respirator. I spent the weekend working outdoors in southwest Wisconsin this weekend where the AQI was over 200, and spent Sunday flip flopping between “can’t breathe from the smoke” to “can’t breathe because it’s too hot and the respirator is making it hotter”. And yet, breathing in smoke is nothing to mess with. We’ve done some informal trialing of different respirators to try to figure out how to make them a bit more bearable to wear: 

• If you do have to be outside working when the AQI is high (respirators are recommended for everyone when the AQI is 100 or higher, and for people with respiratory conditions when it’s above 50), the “cool flow” respirators are more expensive, but they really do help.

• If you wear glasses, you know how annoying it is when they keep falling off of your face because your respirator holds them off of your nose. Getting the N95s with straps that go over the back of your head vs. over your ears helps a lot, because you can put the straps over your glasses, which helps hold them in place. 

• Indoor air quality matters a lot. Try to designate an indoor space with an air filter where you can take breaks and let your lungs rest. 

Crop updates

Beans: Hot days and nights result in fewer, smaller beans and pods. Flowers in beans abort when temperatures stay above 95°F, and hot weather also causes flowers to produce less pollen. Together, this means we are looking at some weenie bean harvests – fewer pods, and the pods that are around are stunted and thin.

We are also getting reports of bean leaf beetle feeding – both on leaves and pods.  At this point in the season, leaf feeding is less problematic, though the pod feeding, while it is cosmetic, is enough for customer rejection.  There are a variety of products available for conventional growers, but we don't have any good data on effective organic controls. Check Pre-Harvest Intervals (PHI) carefully when making applications. Weeding, mowing, and crop residue destruction will make the beetles' lives harder and help reduce next year’s populations.  

Garlic: It’s garlic harvest time!! As a general rule of thumb, garlic is ready to harvest when 40-60% of the leaves have browned. If you’re not sure, you can harvest a few bulbs and cut them in half. The garlic cloves should completely fill the skins. We don’t yet have a great sense of how peoples’ garlic crops are looking as they are harvested, but we’ll share updates here as we see more over the next week or so. If you’re seeing some funky cloves, review the Growing garlic in Minnesota guide for a list of diseases, mite damage, and other problems that can impact garlic bulbs. 

Managu: It’s flea beetle city in many of the managu fields we’ve seen this week. 

Vine crops: Vine crops are the star of the show this week, with all kinds of issues cropping up: 

Wilting: Is it bacterial wilt or squash vine borer? If you’re seeing plants here and there with extreme wilting, it could be one of two things: bacterial wilt, a bacterial pathogen spread by cucumber beetles, or extensive stem damage from squash vine borer larvae. Look around the crown of the plant – calling cards of squash vine borer are holes in the crown and a wet, sawdust-like pile of frass. Bacterial wilt is more common in cucumbers and melons, and less common in squash and pumpkins. If you make a fresh, vertical cut through the stems of an impacted plant you can something get what plant pathologists called a bacterial stream. Rub the two halves of the cut stems together, then slowly bring them apart.  If you see a goo stringing between the two halves (if you spend  time watching food content online, think like a cheese pull), that is a symptom of bacterial wilt.

Is that powdery mildew?: This is the time of year when powdery mildew can get started – we first see this disease on the underside of the oldest leaves in the thickest part of the canopy. A common question this time of year is if white areas on summer squash leaves are powdery mildew, or something else. Some varieties just have white patches, they will be symmetrical, roughly angular, and are most often seen over the veins. Nothing to worry about here, this is just an appearance some varieties have.

The white spots on this zucchini leaf are just something some varieties do, and are no cause for concern. Photo: Marissa Schuh, UMN Extension.

Bitter cucumbers: Bitterness is caused by compounds called cucurbitacins, which are heavier at the stem end and under the skin. Cucurbitacin production is generally linked to weather - we usually see bitterness following cool weather during fruit production, but big temperature swings of 20 degrees (F) or more can also cause bitterness. Drought stress is another factor. Temperatures have certainly been fluctuating over the last few weeks, and drought stress is widespread across the state, so it’s not surprising that we’re seeing some issues with bitterness. The final thing that plays a major role is variety selection. Older cucumber varieties with thicker skins may be more likely to produce bitter compounds than newer varieties that have specifically been bred for reduced bitterness. 

Squash bug time: This is the time of the season when squash bug starts rearing its head.  Scout for coppery eggs, which you can scrape off if you are only finding a few. If you are finding a lot of eggs, make a note to spray in roughly a week when eggs hatch – the small, grey nymphs that emerge from these eggs are much easier to kill than the larger nymphs and adults we will be dealing with a month from now.  Conventional growers have a variety of options, the best bet for organic growers is something like Azera, which has two active ingredients (azadirachtin and pyrethrins).  See the Midwest Vegetable Production Guide for more information.

Squash bug nymphs (left) and eggs (right). Small, recently hatched nymphs that are still clustered together are the easiest to treat. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org

Tomatoes: We’re so close to tomato season, but they’ve been generally slow to ripen in fields (hot nights slow tomato ripening). Judging by all of the leaf curl (a heat stress response) and sunscald we’re seeing, the tomatoes were struggling as much as we were with last week’s heat.  In field plantings, leaf spot diseases are getting started. You can check out our article about the main leaf spot causers, how to tell them apart, and what to do about them in this article.

In the high tunnels, tomato leaf mold is starting to crop up, most likely due to the high humidity we had last week. All the good cultural practices (venting, pruning, weeding, drip irrigation) aren’t enough to stop this fact-of-life disease of high tunnel tomatoes. Managing this disease with fungicides is tricky – research has shown there are a lot of different strains out there, and each strain responds differently to fungicides (and resistant varieties). Copper products can help, the New England Vegetable Guide lists Oso 5%SC as another option.  Make sure to clean up tomato residue thoroughly at the end of the season.