Weekly vegetable update: 6/15/2022

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

This week included a variety of extremes: heavy rainfall in some places, no rain in others, and our first really hot day of the season. Most crops are catching up quickly after the cold spring, and the rest of the month is supposed to be hot. Take some time this week to come up with a heat safety plan for yourself and your employees, and to take stock of insects and diseases as they start to ramp up for the season.

Crop updates

• Lettuce: This spring has been excellent for lettuce. Climatologists are predicting a hotter than normal second half of June, so as we move into summer plantings, make sure you're prioritizing heat tolerant varieties. I've started to see scattered reports of bottom rot, which can be exacerbated by high humidity and limited airflow as lettuce heads begin to mature. 
  

• Garlic: A few growers have begun to report the emergence of scapes in their garlic. Ideally, cut each scape by hand as early as possible; waiting to cut can reduce bulb yields. It's worth taking the time to do this very carefully, as research in Ontario has shown that damaging the leaves in this process can significantly reduce bulb yields. For growers who are really excited about garlic, you can learn more about these results in this week's Ontario vegetable update. 

 

Remove scapes carefully to avoid damage to leaves. Photo: Natalie Hoidal

• Onions: So far the cool weather has kept onion thrip populations low, but as the weather warms up and stays warm, start scouting more regularly for onion thrips. Many growers had high populations last year. Check out the Midwest Vegetable Production Guide for pesticide recommendations.
  

• Peas: The first few field grown peas are arriving, at least in Southern Minnesota. If you're seeing bleached white looking new growth on your pea plants please let me know - I am tracking a potential problem and wondering how widespread it is. 
  

• Asparagus: Asparagus season is nearing its end. Here are three ways to know that you should stop harvesting soon (taken from the Growing Asparagus in Minnesota Guide): 1. Spear growth and emergence has slowed down considerably, 2. Spear width is less than pencil size, 3. Heads are ferning out (expanding) on spears less than 6 inches tall
  

• Cole crops: Cole crop success has been highly variable. Some growers are reporting a fleabeetle-pocalypse, while others are seeing relatively low populations compared to previous years. This has significantly impacted growth, with some Brassica plants way behind schedule. Many growers are moving beyond turnips and radishes into the more exciting realms of kohlrabi, bok choi, and even some broccolini. Now that all of our Brassica pests are here, make sure to read Marissa's article for a management refresher. 

 

Light to moderate flea beetle feeding damage on turnips. Photo: Natalie Hoidal

• Tomatoes: The very first tomatoes are ripening in high tunnels. This is the time of year we start to get a lot of questions about blossom end rot and yellow shoulder, as the first fruits tend to be the most severely affected, at least for blossom end rot. The key is usually consistent irrigation.
  

Problems in the field / things to do this week

Beating the heat

As we experience more frequent bouts of extreme heat, it's important that you're keeping yourself and your employees safe. A farmer / colleague shared this table with me over the winter, which includes the US Army's recommendations for how much time you need to rest and how much water to drink at different temperatures. I tend to think of the army as being pretty intense, and so it was really interesting to see how strict their guidelines are for taking breaks. You can read the full publication here, but most of the information is included in the table below.  

Of course, our plants are stressed as well. Keeping fields well watered when you anticipate high temperatures is one of the best tools we have for reducing plant stress. Shade cloth can also be a valuable tool for cool season crops grown into the summer. 

 

Chart: US Army Public Health Center

Sulfur deficiencies, an unexpected side effect of reducing coal emissions

Typically, we don't think of Minnesota soils as being sulfur deficient, so sulfur is not part of the routine soil tests recommended to growers. However, in diagnosing a case of bleached peas this week, I learned something new. Apparently alfalfa growers have been seeing more and more sulfur deficiencies in recent years, as alfalfa is particularly sensitive to sulfur. This has been attributed to the reduction of coal emissions. Historically coal plants emitted sulfur into the atmosphere, which deposited into fields. As we've moved towards cleaner sources of energy, atmospheric deposition of sulfur into agricultural fields has decreased. What does this mean for growers? Unless you're seeing problems, probably not much. But, next time you do your routine soil testing, it probably wouldn't hurt to include a sulfur test to get a baseline reading of your soil sulfur levels. 

 

Here's a photo of a sulfur deficiency in melons from G. Burst at the University of Maryland for reference. Unfortunately it looks a bit like nitrogen deficiency: chlorosis on new leaves. Anytime you suspect a nutrient deficiency in your crops, it's best to do a foliar test, in addition to your standard soil test, as nutrient deficiencies can be difficult to distinguish from one another. 

 

Sulfur deficient watermelons, Photo: G. Brust, University of Maryland

 

Flooded fields

I've stopped doing weather forecasts this year because honestly, the weather has been so random. I was in Waseca this week where they received 4" of rain over the span of a few hours and the fields were completely flooded. But less than an hour away, growers are having to irrigate because they haven't seen rain in a week. Here are some general tips for dealing with flooded fields: 

• Don't do what I'm doing in the photo below. It's tempting to go out and inspect the damage, but it's better to wait it out until the field has drained a bit. Moving through wet fields and inspecting plants can lead to soil compaction, and you can spread disease in the process.
• After a heavy rain fall, wait until your crops have dried to fix any trellising or to prune out damaged plant parts.
• Scout your crops frequently following extreme weather events and consider spraying if you see any signs of disease to ensure that it does not spread further via wounds (e.g. wounds from hail damage, stems snapping off in heavy winds, etc.) You can send photos to our team via the form below to help you identify any issues you're seeing. 
• Any edible portions of produce were touched by floodwater may be contaminated and should not be considered safe to eat.

Corn plants after 4" of rain in Waseca this week. Photo: Natalie Hoidal

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.