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Weekly Vegetable Update - May 29, 2024

Author: Marissa Schuh

Growers are plugging away with planting and other early season tasks in between rains. This May has been one of the wettest in recent years – quite a change of pace from the last few Mays we had.

Our crops have moisture, but so do our plant pathogens
We’ve gotten some questions about potential fungal diseases this week, which makes total sense – we’ve had rain, humidity, and dew.

If this moisture keeps up, we will continue to see plant diseases show up. Some reminders on general practices that help prevent a wide range of pathogens…
  • Work in field when they’re dry, especially if you’re pruning, tying, or staking plants
  • Mulches between and within rows can reduce splashing and movement of some pathogens
  • Increase airflow by using proper plant spacing, weeding, mowing field edges, and tying/staking
  • Fertilize plants according to soil test and nutrient management recommendations
  • Fungicides are most effective when used as soon as the disease is detected. Products don’t cure the plant or reverse damage, instead only slowing the disease spread. Scouting regularly helps catch disease early enough that fungicides are still a useful tool.
Feel free to reach out (Marissa's cell is 612.460.7462, or to your local extension educator) for help with diagnosing issues. Information on the Plant Disease Clinic is at their website.

High winds and cool nights can damage transplants
While we have had moisture, we’ve also had some very windy days and cool nights. Tender transplants are vulnerable to these conditions.

When it comes to wind, crops can be damaged either directly by strong winds (often referred to as whipping) or by blowing sand (sandblasting). Windbreaks help prevent both – whether they be large and permanent (wind row, trees) or small and temporary (strips of cover crops every few rows).
A pepper plant with yellowed scarring from sandblasting. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo,

When it comes to cold, we haven’t touched freezing, but for our warm season crops, it doesn’t need to get to freezing for them to be unhappy. Sweet corn needs warm soil to germinate (60-95°F), and once emerged, likes things above 50°F. Cucumbers like it above 60°F, and peppers like it above 65°F. It hasn’t quite been warm enough for these crops to be growing well or quickly. Many of the pictures we’ve gotten asking about disease include a few leaves that look like they have a little bit of cold damage. This often looks like amorphous patches of yellow or white, often on the older leaves.
A young cucumber plants with cold damage. Photo: Doug Doohan, Ohio State University/ OARDC,

Again, cover crops windbreaks can help with making more favorable microclimates for transplants. The shelter helps keep the area above the soil warmer than higher up in the air, and the humidity the microclimate creates also helps converse soil moisture and keep things warm.

Herbicide drift
We are well in the window where herbicide drift happens. One active ingredient commonly associated with off-target damage, dicamba, has use cutoff dates specific to Minnesota. South of Interstate 94, certain dicamba containing products (XtendiMax®, Engenia®, and Tavium®) cannot be applied after June 12. North of Interstate 94 they cannot be applied after June 30. There are also additional restrictions on air temperature with no application allowed above 85°F. Applicators are required by law to follow these restrictions along with any that may be on their product’s label. On the upside, this may be the last time you read about XtendiMax®, Engenia®, and Tavium® in one of these updates, as current regulations stand, this is the last year these products are available for limited sale and can be used.

The University of California has a tool you can use to look at what damage caused by different herbicides looks like. Dicamba and 2 4-D are two of the most common active ingredients being used and are prone to drift. They both are auxin herbicides, meaning they impact plant hormones and the way a plant grows. Susceptible plants that have been exposed to these types of herbicides often have twisted and distorted leaves and stems, as well as stunted growth.
A pepper plant with 2, 4-D herbicide injury. Note stunted, cupped leaves, wiggly veins, and curving stems. Photo: David B. Langston, University of Georgia,

Another clue in deciphering if what you see is herbicide drift is to look at neighboring vegetation, such as trees or weeds. They can display the same types of cupping, twisting, and distortion that vegetables do.
Sumacs are a common tree in Minnesota, this one is displaying symptoms of dicamba drift. Photo: William Jacobi, Colorado State University,

If you suspect dicamba related damage to your vegetables or fruits, there is a specific complaint process you can access here. For an unknown or non-dicamba product, you can pursue the process at this link. These processes are the main way to get the testing done to confirm herbicide drift. Also, consider listing your farm on DriftWatch registries and communicating with neighbors beforehand to help avoid possible issues.

Canada thistle management
Canada thistle is just about to flower in many spots, meaning we are in a window where Canada thistle management is extra effective. Managing this perennial weeds is time consuming, and our efforts are most effective when we time management actions for when this weed’s perennial roots are pushing out more energy than they’re taking in – which occurs as the plant emerges in the spring, and then again as the plant sets buds and flowers.

If you have this weed in your production areas, aim to remove new shoots while they are still small, and mow/weed whack plants that get away from you as they set buds.

This weed often creeps in from ditches and other field edges, mowing on field edges can be a good task when fields are too wet to work on.
Bushwacking Canada thistle is a lonely task, but you aren't the only thing getting after Canada thistle. The yellowing in these Canada thistle leaves is caused by a bacterial pathogen that infects the plants. Photo: Shane Bugeja, UMN Extension.

For more info on Canada thistle biology and management, check out this blog post from last spring.
Another enemy of Canada thistle? Canada thistle bud weevil, which feeds on the flower buds of invasive thistles (yay!) and native thistles (boo!). Photo: Shane Bugeja, UMN Extension.

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