Weekly vegetable update 5/25/22

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

It's been a busy week of quickly planting as much as possible between rain events. Pretty much everyone is a week or two behind due to the cold spring, but the week ahead should bring warmer weather and better conditions for heat loving crops.

Crop updates

• Cucurbits: Most growers don't have their cucumbers, melons, and pumpkins in the field yet, but the week ahead of planting is a great time to start thinking about cucumber beetle management. Managing this pest is complicated and requires a multi-faceted approach. One of those approaches is to use an attractive trap crop BEFORE you plant your main cucurbit crops; if you have some quiet time while you work this week, check out the Vegetable Beet podcast episode titled "Ugh Bugs! Organic Cucumber Beetle Management". 

Cucumber beetles tend to show up right when cucurbits germinate / enter the field. Photo: UMN Extension

• Sweet corn: Soil conditions are still cold for most varieties of sweet corn. Last year at this time some farmers had already planted a couple of successions. With the warm weather in the forecast, it should be safe to plant very soon. Check the soil temperature maps in your area (linked below in the weather report) and wait until temps get closer to 60/65 consistently. The seedcorn maggot forecast predicts that the first generation has emerged already in the southern half of the state, and will be out across the entire state by the end of this week. Seedcorn maggot is most destructive during cold, wet springs when germination is slow, so waiting for warmer soils that will allow quick germination will help you to avoid issues this year. 

• Beans: Customers often expect green beans early in the season, so it's tempting to get your green beans planted early. However, similar to sweet corn, green beans are susceptible to seedcorn maggot during cold and wet spring conditions. By either transplanting or waiting until your soil warms up, you'll reduce the risk of seedcorn maggot damage. 

Bean seedling with seedcorn maggot damage. Photo: Erik Burkness

• Asparagus: Asparagus harvest continues. I've noticed asparagus beetle damage on pretty much all of the locally grown asparagus I've seen so far this spring, including asparagus sold at farmers markets and stores. Check out the article Annie and Marissa wrote last week about asparagus beetle management if you want to explore spraying.
  

• Cole crops: Despite the heavy rains, it seems like folks are seeing relatively good germination on radishes, turnips, and other direct seeded Brassicas. I've heard mixed reports of flea beetles; some growers haven't seen them at all yet, and others have lost entire crops already. Review the management recommendations for flea beetles before they start to pick up if you're not already seeing problems. I expect we'll see some more bolting this week as temperatures increase. Last week I wrote about bolting and why we actually see it more in years where we've had cold weather.
  

• Tomatoes and peppers: Plenty of growers planted tomatoes and peppers last week, and quite a few saw cold damage. While we did not see freezing temperatures in most of the state this week, prolonged temperatures below 50 degrees can lead to stress. Unfortunately I don't have any good photos of cold stressed tomatoes, but I found the photo below from an article by Barrero-Gill et al. (2016) showing seedlings exposed to 4 degree C temperatures (39.2 degrees F) for 5 and 10 days. Plants show signs of wilting, and chlorosis that can sometimes look like sun scald.
  

 

 

If your plants are experiencing cold stress, they should recover, especially with the warm week ahead. For those of you waiting to transplant, make sure to give your plants a bit of extra TLC in the hardening off process as they transition from a very long, dark spring to hot summer conditions this week. 

• Garlic: If you still need to fertilize your garlic this spring, we're reaching the end of the fertilization window. Fertilizing too late in the season can delay bulb development and lead to lower yields. 
  

• Potatoes:  It seems like most growers finally have their potatoes in the ground. For the last two years, we've been working with farmers at Clover Bee Farm, Shepherd Moon Farm, and Big River Farms to test non-chemical management strategies for potato beetles. Check out the video from the trials to see what the farmers thought of strategies including trenches, row cover, straw mulch, trap crops, and flaming.
  

Vegetable weather report

As the current rainy weather system moves out of Minnesota, we're looking at a warmer and sunnier weekend with low humidity across the state. We should see high temperatures early next week, reaching nearly 90 in Southern Minnesota on Monday, and low to mid 70s across the Iron Range and North Shore. The warm weather will also bring more humidity, and also more rain early to mid next week, with Northwestern Minnesota receiving an estimated 2+ inches of rain this week more like one inch across central Minnesota, and less in Southeast MN. This means many growers might have to spend the weekend planting to catch up before the next round of rain.

 

Soil temperatures stayed pretty much the same this week, and in some cases were colder than last week. While some growers have started planting heat loving crops like tomatoes and peppers outdoors, the soil is still a bit colder than would be ideal for planting.  The following tables provide a snapshot of soil temperatures across the state. For more detailed info, see https://app.gisdata.mn.gov/mda-soiltemp/

Soil temperatures from MDA stations, data collected to 6’’ depth

Station location	Nearest major town	Coldest soil temperature in the last 7 days (approx.)	Temperature on May 25, 2020 (approx).
Blue Earth	Albert Lea (Iowa border)	55 º F	58 º F
Russel	Marshall	52 º F	62 º F
Henderson	St. Peter / Belle Plaine	54 º F	64 º F
Hoffman	Alexandria	47 º F	51 º F

Soil temperatures from ND-managed stations in MN

Station location	Nearest major town	Approximate turf soil temp on May 25  (4’’)
Sabin	Fargo / Moorhead	55 º F
Mavie	Thief River Falls	52 º F
Fox	Roseau (Canada border)	54 º F

Problems in the field

Time to talk about herbicide drift

Many field crop producers are behind this year for the same reasons that specialty crop growers are. For some, this may mean more pressure to squeeze herbicide applications into short windows of time, and potentially could lead to more applications during windy conditions. Talk to your neighbors, and even consider calling local co-ops to let them know you're farming specialty crops that are sensitive to drift (even if you've done it before it doesn't hurt to call again and remind them). Growers can also sign up for DriftWatch.  

Dicamba, a growth regulator herbicide that is notorious for volatility, has a new set of rules this year: 

• The application cutoff date is June 12th everywhere south of interstate 94 in Minnesota. 
• For growers north of interstate 94, applications are allowed until June 30th. 
• Applications are also banned when the forecast for the day exceeds 85 degrees Fahrenheit. 

If you suspect drift damage, file a complaint with the Minnesota Department of Agriculture, and they will send someone to investigate and help you navigate next steps. 

 

Phenoxy herbicide damage on tomato transplant. Photo: Rebekah D. Wallace, University of Georgia, Bugwood.org

Connect with the fruit & vegetable team

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 hoida016@umn.edu, and you can submit questions and diagnostic help below.