First weekly vegetable update of 2023: 5/17/23

UNIVERSITY OF MINNESOTA EXTENSION - www.extension.umn.edu

 

Following a slow, wet spring, the growing season is finally picking up. Our team of educators has been visiting farms across the state, and in general, everything is extremely delayed due to wet soils. Some fields are still flooded following heavy rainfall events this week. Nonetheless, we’ve seen plenty of exciting things in high tunnels and greenhouses already.

Since things are so delayed, we’re foregoing our usual series of crop-by-crop updates this week and instead sharing some general observations.

 

Soil testing reflections

 

Many of you have likely heard about our 100 farms project: our team is visiting 100 vegetable farms this month to complete a series of chemical, biological, and physical soil tests with the goal of developing a better baseline understanding of MN vegetable farm and high tunnel soils. We’ve learned a lot already just from observations, and we’re excited to see what the test results show us. A few key observations include:

  • Infiltration rates have mostly been quite slow in field conditions due to saturated soils. However, tunnels and fields with many inches of compost have had extremely fast infiltration rates (as in, less than 1 second for 1 inch of simulated rainfall to infiltrate the soil - the average has been more like a few minutes). You can easily do an infiltration test yourself with a soup can - it takes a few minutes, and you’ll likely gain some insights about your irrigation management strategy.
  • In some high tunnels, we noticed visible salt accumulation on the soil surface. This is one of the issues we’re exploring in our study - we want to learn more about the influences of irrigation water and inputs on salt build-up.
  • At farms that rely more heavily on tillage, many educators noticed a distinct hard pan in the soil. In high tunnels, farms that used broadforking generally seemed to have better infiltration rates and were less likely to have a hard pan. We’ll have more data to really explore this observation soon.

 

Salt accumulation on soil surface. Photo: Shane Bugeja

 

Plant problems

 

Every year we receive photos of transplants with bleached leaves like the photo below. There are two main factors that can cause symptoms like this, and another less common cause:

  • If plants experience cold damage, the epidermis (outer layer of plant tissue - sort of like skin) can become detached or loosened, resulting in bleached-looking white leaves.
  • If plants experience an abrupt change in light or are not sufficiently hardened off, they can become sunburnt.
  • Certain herbicides can also cause similar symptoms, but they are not very commonly used, and are unlikely to enter into a high tunnel or greenhouse.

 

 

Farmer submitted photo

 

Pest updates

 

Crafty Cutworms

 

Cutworms have always been an issue for row crops as well as vegetables in Minnesota. There are several species of these destructive insects, with some migrating to Minnesota from warmer states to our south and others who overwinter in our soils. Black cutworm, which is considered a migratory species, has been popping up in pheromone traps this spring. While most of the season has been (relatively) quiet, a large rain system last week brought a notable increase in activity. High tunnels may be a wild card with black cutworms, as there is concern these animals can overwinter in these warmer areas. Regardless, keep your eyes open and let us know if you suspect cutworm damage to crops (or even weeds) in your tunnels. Identifying exactly which cutworm caterpillar you have can be difficult, as the majority are dark colored and broadly look similar. Capturing them is also annoying, as the caterpillars do their “work” at night, and hide in the soil during the day. Thankfully, black cutworm moths are easier to identify due to their “dagger” patterns on the lower part of their wings.
 

Thrips and mites

 

Around this time every year we start to see damage from thrips and mites in seedlings / transplants grown in greenhouses, and in early season high tunnel crops. Often it’s difficult to notice the damage until a few weeks after feeding occurs. For example, in the photos below, you’ll notice feeding damage from thrips on peas that likely occurred a while ago, and damage in the growing points of peppers from mites. In both situations, the damage became more noticeable as the plants grew. While it’s very difficult to completely prevent these problems, using good sanitation, providing a lot of airflow, and beginning the season with beneficial insects can all help to prevent damage from these common greenhouse pests.
 

 

 

Photos: Natalie Hoidal

 

Cabbage maggot

 

Degree day models show that cabbage maggots are now in flight across the southern half of the state. The best way to prevent damage is to cover any Brassica crops as soon as they are planted / transplanted. This will also help with early season flea beetle management. Read more about cabbage maggot here.

 

Vegetable weather report

 

Soil moisture

 

Following the wet winter and spring, most of the state is no longer experiencing drought. The seven day forecast shows about 1/10 of an inch of rain next week for most of the state, but closer to an inch in the far Northeast. This should give peoples’ fields a chance to dry out a bit more as we wait for soil temperatures to increase.

 

 

Risk of frost

 

The DNR publishes summaries of annual normal temperatures from 1981-2010, which they use to estimate last spring frost dates (less than 10% risk of 32 degree weather). For areas south of Willmar and Minneapolis the risk of frost has likely passed, but we could still see a frost in Northern MN. Click on the link to see frost dates for your area.

 

Soil temperatures

 

Even if the risk of frost has passed, it’s important to pay attention to soil temperatures to guide planting. Soil temperatures are warming quickly across the state, but are still cooler than would be ideal for planting warm season crops like tomatoes, most varieties of sweet corn, green beans, etc. The Minnesota Department of Agriculture publishes daily updated soil temperatures for major field crop growing regions of the state. Data is compiled from MDA managed stations in the Southern half of the state, and NDAWN managed stations in the northern half. As such, the data is presented slightly differently. The following tables provide a snapshot of soil temperatures across the state. For more detailed info, seehttps://www.mda.state.mn.us/protecting/soilprotection/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 17, 2023

Gordonsville

Albert Lea (Iowa border)

46.5º F

48 º F

Henderson

St. Peter / Belle Plaine

56.5 º F

59.5 º F

Wheaton

Wahpeton / Elbow Lake

55.6 º F

52 º F

 

Soil temperatures from ND-managed stations in MN

 

Station location

Nearest major town

Average turf soil May 17, 2023  (4’’)

Sabin

Fargo / Moorhead

60 º F

Fox

Roseau (Canada border)

60 º F

 

Publication: 

The Drummer and The Wright County Journal Press

PO Box 159
108 Central Ave.
Buffalo MN 55313

www.thedrummer.com

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