Weekly vegetable update - May 28, 2026

 Authors: Natalie Hoidal & Marissa Schuh

Gosh it was hot yesterday.  Temperatures look like they will continue to be in the 80s for much of

Minnesota for the foreseeable future. The NOAA seasonal outlook released last week calls for equal chances of above or below average temperatures, and below average precipitation for the rest of the season. More of the state has been put into the "abnormally dry" category by the US drought monitor, but you have been getting so much field prep and planting done that you probably already knew that.

Adjusting to heat

This first heat wave of the year is tough. Our bodies are not acclimated to the heat, and the shift from sweatshirt weather to 90 degrees doesn’t just feel brutal, it can actually be dangerous. The National Institute for Occupational Safety and Health (2018) provides the following recommendations for acclimating your body to heat:

• For new workers, the schedule should be no more than a 20% exposure on day 1 and an increase of no more than 20% on each additional day.
• For workers who have had previous experience with the job, the acclimatization regimen should be no more than 50% exposure on day 1, 60% on day 2, 80% on day 3, and 100% on day 4.

Even when your body is acclimated to the heat, NIOSH recommends more rest than most farmers allow themselves. At 88-90 degrees fahrenheit, the guideline is 30 minutes of rest for 30 minutes of work, and 0.75 quarts of water per hour for “moderate work”.

Check out our heat and safety for farmworkers page for more information. You can also access a printable heat safety guide here.

Fine tuning cultivation

The dry weather has made field prep, planting, and cultivation run smoothly.  Young plants are the most susceptible to competition from weeds.  If you are managing annual weeds with cultivation, timing and depth will drive how effective time spent on the tractor or behind the hoe will be.

• The best time to cultivate weeds is when they are very small. Most weeding tools, be it on a tractor, wheel hoe, or just in our hands, are designed to run shallowly and cut or uproot white thread stage weeds. White thread stage plants have just germinated, they have one thin root, and the first two leaves (the rounded cotyledons). Once these weeds grow a little more, they give their first set of actual leaves, that are able to make sugar from the sun, and a more developed root system, which can use that energy to power further growth and establishment. Once this growth has happened, a lot of tools don’t really work anymore, because the weeds can re-root. You might need to pop a squat and brush the soil to see these whit thread stage weeds, often times we can't see them when standing.
  
• The best depth for cultivating weeds is shallow, 1.5 inches or less. The very top of our soil profile is where weed seeds get the signal that they have what they need to germinate, push through the vulnerable white thread stage, and actually get established. When we cultivate deeper than 1.5 inches, we can bring up fresh seeds into this germination zone, and will have another strong flush of weeds in a a week or two.

Obviously, there are a lot of nuances here by tool, weed, and soil type, but keep these principles in mind. Want to learn more and get hands-on experience in trying and adjusting tools? We still have 3 hands-on workshops focused on cultivation with open spots across the state later this summer.

Attendees at a field day check a cultivated bed to see if the implements are having the intended affect. Photo: Marissa Schuh, UMN Extension.

Crops updates

Asparagus: Harvest has been slow for some farmers, likely due to the cool weather. We usually see production wind down towards early June, but it can continue to mid June for many growers. When you start seeing spears that are pencil size or small, your plants are telling you they are ready to take a break.

Brassicas: At this point in the season, you should be switching to heat tolerant summer varieties. Three heat tolerant broccoli varieties for June planting that stood out in our 2021 and 2022 on-farm and research station trials were Wolfman, Green Magic, and Eastern Crown.

Flea beetles are out. The younger the plant, the more susceptible they are to intense flea beetle damage, how much continued flea beetle damage matters will depend on your farm’s local flea beetle pressure, and what part of the crop you harvest. For more preventative management….

• Row covers are the best protection you can get, place them just after transplanting.

• Kaolin clay can provide a physical deterrent to feeding. Kaolin clay can be hard on sprayers, but transplants that are about to be planted can get a dunk while still in the tray. Kaolin clay is difficult to wash off plants, so isn’t a great choice for when plants get older and we are closer to harvest.

If the flea beetles are already attacking your plants, consider a pesticide application.

• If 10-20% of the leaf area of plants are damaged, consider spraying.

• Flea beetle damage may be concentrated at the edges of the field or in hot spots in the field. Spot treatments can be effective while saving time and money.

• On the organic side, product performance is mixed. Pyrethrin and spinosad products have performed the best, but even then, they often don’t give great control.

• For conventional pesticide options, see the Midwest Vegetable Production Guide.

Scarred shothole feeding from flea beetles. Look closely for the shiny black beetles themselves. Photo: Marissa Schuh, UMN Extension.

Caterpillars are also showing up. Diamondback moth caterpillars are around, and we observed Cabbage White Butterflies, the adult form of imported cabbageworm, looking for places to lay eggs on a farm in Southeast Minnesota this week.

Seeing this butterfly in your fields? Scout for caterpillars next week. Photo: Johnny N. Dell, Bugwood.org

Garlic: With hot, dry weather and a lot of planting left to do, it’s easy to forget about your garlic this time of year. Right now is when garlic bulb development is happening, and consistent moisture is so important. This is the “critical period” for irrigation in garlic. 

Vine crops: Cucumber beetles are emerging. This is another tough bug, often best managed with row covers on extra vulnerable, young plants.  For a round up of management, see “Managing tricky vegetable pests: Cucumber beetle.”

Sweet corn: Stands are uneven. We’ve seen a lot of cold damage, but most plantings should grow out of it.