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Weekly vegetable update 6/8/2023

Authors: Natalie Hoidal, Marissa Schuh, Anthony Adams, Emily Hansen

Growers are still catching up from a late spring, and many farmers markets will open this weekend. We’re expecting hot, dry weather in the weeks to come along with air quality concerns. Our updates this week focus mostly on preparing plants and people for these conditions.

Crop updates

We reviewed some old vegetable updates from around this time in previous years, and many growers are still behind on a lot of crops relative to 2020 and 2021.

Peppers seem to be getting hammered the worst of all vegetables by cutworms this year. There was some interesting discussion in a Wisconsin vegetable listserv about using toothpicks or skewers next to plants to prevent cutworms from doing the final cut. We can't refer to any research studies about this, but it seems like any easy strategy to try if you’re at the end of your rope with cutworms.

Tomatoes are reaching the point where staking and pruning should begin. The weather is ideal for this: not too hot (which can cause stress), but dry enough that plants can quickly recover from pruning wounds. We've also been seeing reports of stem girdling from black plastic and black landscape fabric. This is common when plants are transplanted in hot weather. Temperatures under black plastic can be 40-50 degrees hotter than ambient air temperatures, and when the air escapes through the holes created for transplants, this hot air can damage the stems of young pepper and tomato plants. The easiest way around this is to irrigate really well to keep the soil temperature cooler on hot days early in the season. Other approaches are to switch to white plastic mulch or to use shade cloth. Here's an article about it from our colleagues in Delaware.  

Tomato with a girdled stem from heat stress. Photo: Natalie Hoidal

Asparagus: While most growers have no problem selling their asparagus promptly, make sure you’re following best post-harvest practices if you need to store your asparagus more than a few days before you sell it. The optimal storage temperature for asparagus is 32 degrees fahrenheit with 95% humidity. Asparagus with looser tips will go bad faster, so try to sell these spears towards the beginning of the day at farmers markets, and save the spears with tighter tips for later since they keep longer. 

Beans: We're seeing defoliation on bean plants from bean leaf beetle.The threshold for treatment is 1 beetle per row foot or 25% defoliation. 

Bean defoliation, likely caused by bean leaf beetle. Photo: Natalie Hoidal

continue to grow and be fed upon by flea beetles and caterpillars. Diamondback moth has been the main caterpillar we’ve seen so far, but imported cabbageworm butterflies are out. 

Diamondback moth pupate in silk cocoons on brassica leaves. The darker the insect inside the silk is, the closer it is to moth emergence. Photo: Russ Ottens, University of Georgia,

Strawberries are starting to come in on some farms. We are getting reports of issues related of delayed flowering (this can be caused by too much nitrogen prior to flowering), thrips damage (bronze colored, seedy berries), and leather rot (smelly, brown, rough skinned berries). For more info on these and other strawberry pests, see the our page on strawberry farming.

Thrips-damaged berries are smaller, misshapen, and discolored. Photo:Mary Ann Hansen, Virginia Polytechnic Institute and State University,

Leather rot infected strawberries. Photo: Suzanne Wold-Burkness.

Weed Notes

Weeds in the field are of all ages – some winter annuals are getting ready to set seed, some in the white thread stage. For those of you using post-emergence herbicides, remember that products work best on weeds shorter than 3 inches, okay on weeds 3-6 inches tall, and poorly on weeds greater than 6 inches tall.

Hot, dry weather this month

While the NOAA 3-month forecast shows that the Midwest is equally likely to be above or below average in terms of both temerature and rainfall this summer, their 30 day forecast projects hotter and drier weather than usual for the month of June.

Hot weather aids the biology of aphids and spider mites, both of their populations boom during periods of hot weather. An increase in aphids can also lead to increased incidence of viral diseases, with more aphids present in the landscape to move more viruses around. Be on the lookout for these issues as the hot and dry weather continues.

Outlook maps: National Oceanic and Atmospheric Administration

Soil moisture sensing

During hot, dry weather, it’s especially important to keep up with irrigation. Soil moisture monitoring can help to inform irrigation scheduling and can provide peace of mind to growers who want to be sure that their crops are getting enough moisture. There are two primary types of sensors:
  • Sensors that measure volumetric water content, or
  • Sensors that measure soil tension when placed in the soil profile.
Sensors that measure tension are more common among small-scale growers. There are a variety of affordable and easy to use models. Some models can be connected to computers for continual monitoring, others are simple sensors that need to be checked manually. You can read more about soil moisture sensors and the pros and cons of different models on our Irrigation Strategies for Vegetable Growers webpage.

Air quality reminders

Air quality has been poor due to Canadian wildfire smoke, and while a cooler air front may help clear the air over the weekend, the fires are expected to continue burning beyond this week. We’ve heard from many farmers who are struggling with coughing and asthma, and we’ve shared some updates about recommendations for wearing respirators when air quality gets bad enough. Here are some additional tips:
  • The Minnesota Pollution Control Agency’s air quality forecast: Despite the persistence of the poor air quality, there has been significant day to day variation air quality index (AQI). This two day forecast can help growers to plan for strenuous activities during windows when air quality is projected to be better.
  • In Washington and California, employers are required to implement safety measures for employees that can include respirators, reducing work intensity and increasing rest periods, and improving indoor air filtration when the AQI reaches 151. However, guidance from Washington states that employers are encouraged to do these things when the AQI is above 69.
  • While we have little control over outdoor air quality, we can improve indoor air quality in pack sheds and other indoor spaces. Encourage employees to take breaks indoors in areas with good air filtration.
  • This guide from Washington highlights ways to improve air quality in indoor spaces, including HVAC filters and portable air cleaners.
  • This guide from the University of Washington shows you how to build a low cost air filter with a box fan and a furnace filter.

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