Weekly vegetable update 6/9/2022

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

This was a great week to catch up after a pretty difficult spring. The warmer, drier weather was a welcome change. Soil temperatures are still about two weeks behind compared to last year, and pretty much no soils in the state are maintaining consistent 65 degree soil temperatures. This means plants might be stunted compared to what you're used to, and it also makes seeds germinate more slowly, making them more susceptible to soilborne pathogens and certain insect pests. Heavy rains and planting delays have allowed weeds to flourish. Catching up on weed control will be important in the week ahead.

Crop updates

• Peppers: Many growers have had their peppers in the field for a couple of weeks now. I've noticed slow growth and purple leaves at multiple farms. This is totally normal and to be expected. Cold soils release phosphorus more slowly than warmer soils, and peppers seem to be particularly susceptible to purple leaves early in the season (a sign of a phosphorus deficiency). As long as you've tested your soil recently and you're making P applications accordingly, your peppers will grow out of it as soon as the soil warms up. 

Pepper plant with slight purple leaf coloration. Image: Natalie Hoidal

• Beans: I've seen and heard about bean leaf beetle in a couple of different locations this week. The adult beetles that come out around this time typically defoliate bean plants a bit, and then they disappear after laying their eggs. When plants are small, this early feeding can cause significant damage. Soon these beetles will lay their eggs in the soil. Larvae remain in the soil feeding on roots, and a second generation of adults emerges in late summer. This second generation often feeds directly on bean pods, which can make them unmarketable depending on your markets. For more information about spray thresholds and management strategies, read more about this insect here. 

BLB adult on snap bean leaf (E.C. Burkness, UMN).

 

• Peas: Peas are vining out. I've seen a couple of farms selling pea vines lately; not pea shoots or flowers, just young and tender pea plants to be eaten in salads. It's yet another great way to add some diversity to early spring CSA boxes and farmers market stands in a year where everything is a bit late. 
  

• Asparagus: Asparagus season is wrapping up, with harvests slowing down significantly this week.  
  

• Cole crops: I've begun to notice windowpane feeding on cabbage and broccoli plants in Dakota county, which is characteristic of Diamondback moth. This means we're at the point in the season where growers should be monitoring for cabbage caterpillars and flea beetles, and continuing to manage for cabbage maggot. If you're an avid user of row cover, this should do a pretty good job of protecting your plants from all of these insects. Additionally, I continue to see tons of bolting cole crops, including turnips and radishes. In some cases these roots will continue to expand and form an edible "bulb", but they often become woody and bitter after bolting. Keep a close eye on these crops and consider harvesting earlier than you typically would if you're seeing flower formation. 

Bolting turnip. Photo: Natalie Hoidal

• Tomatoes: Most field tomatoes are reaching a point where they could benefit from a light pruning. It's a good week to do it, as conditions are mostly dry and warm, allowing for quick healing of wounds. I've seen some high tunnel tomatoes that are flowering, and even beginning fruit set. As soon as flowering begins, you enter the "critical period" for irrigation. Ensuring a consistent supply of water helps to prevent issues like blossom end rot. 
  

• Onions and garlic: I'm seeing the very beginnings of bulb formation on onion and garlic crops. This marks the beginning of the "critical period" for irrigation, where consistent moisture is critical to healthy bulb formation. This doesn't mean that they should be consistently wet, just that it's important to try to mitigate major fluctuations between very wet and very dry soil conditions. The wet conditions are of course harder to control, especially when we get multiple inches of rain in a day. But, keeping these crops irrigated during dry conditions is more within our control.
  

Problems in the field / things to do this week

Hot plastic mulch

Every so often I see photos like the ones below, where recently transplanted peppers in black plastic mulch show girdling at the base of the stems. The area underneath black plastic mulch can get extremely hot, and this can result in heat stress / transplant shock. It doesn't happen often enough to universally recommend that folks shouldn't use plastic mulch on peppers, but it happens enough that it's worth mentioning. Making sure peppers (and really any transplanted vegetables) are well watered and hardened off properly can help to prevent this from happening.

 

Photo: Julie Grossman

Terminating cover crops

Organic growers / growers that don't use herbicides in northern Minnesota are terminating their winter cereal cover crops this week. Here are a few things to consider when terminating winter wheat and rye: 

• If possible, wait 2-3 weeks between terminating your cover crop and planting your vegetable crop. Soil nitrogen gets tied up as cover crops break down, and small seedlings will be better able to access it if you wait a couple of weeks.
• The exception to this is if you plan to mow winter wheat or rye and leave it on the surface as a mulch. Consider using a sickle bar mower rather than a flail mower, especially with rye. Flail mowers are amazing for most cover crops, but they can turn rye into a thick pulpy mat.
• There's an assumption I've heard floating around that roller crimpers are not reliable for terminating winter rye and wheat in Minnesota, and that these crops often just bounce back up in our climate, which is a bit wetter than some of the other places where roller crimpers are more common. However, I hear from growers time to time that they do use roller crimpers successfully. If you successfully use a roller crimper, I'd love to hear from you!
  

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.