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Final weekly vegetable update 9/13/23

Natalie Hoidal and Marissa Schuh

With some areas in Northern Minnesota experiencing frost last night, it seems only natural to wrap up our updates for the year. We'll continue to post articles about educational events and relevant topics, but this will be the final weekly vegetable update. Read on for discussions about dry fall soils, topping plants, zombie grasshoppers and soil health equipment grants, and don’t forget to let us know what you thought of this season’s updates by filling out our survey.

Dry soils and end of season field work

Our 100 farms project team has been visiting farms and doing follow-up soil sampling this fall at 10 of the 100 farms included in the original project. The goal of this follow-up project is to better understand how phosphorus is moving across and through farm landscapes, and so it involves taking deeper than usual soil samples, including some 1 meter cores. For the most part, the soil on most farms has been extremely dry, to the extent that we often haven’t been able to get our cores deeper than 6 inches into the soil.

Soil sampling in really dry soil. Photo: Christy Dolph

What does this mean for fall field work? While in general dry soil is less prone to compaction than wet soil during fall tillage and when tractors or other heavy equipment pass over the soil. However, very dry soil is also more prone to soil erosion, and soil disturbance can fracture dry soil, leading to clods that are not easily broken up later. Read more about the dynamics of soil disturbance and soil moisture in this article from Iowa State Extension. Some tips for managing residues in the fall during drought conditions include:

  • Rather than tilling residues into the soil, consider chopping residues with tools like flail mowers, and leaving them on the surface. Not only does this avoid tillage, it leaves a mulch layer on the soil that can help to conserve soil moisture.
  • If you are planning to plant a cover crop, you will likely need to irrigate quite a bit to get the cover crop going. Keeping living roots in the soil will help to reduce erosion next spring.

Topping plants in preparation for cold weather

As we’ve reached freezing or near freezing temperatures in many parts of the state, we’ve received a few questions from growers about topping plants. The idea of topping plants - a practice most commonly done with tomatoes and Brussels sprouts - is to remove the apical meristem(s) (growing points) of the plant, which encourages the plant to shift its resources into ripening its existing fruit vs. investing in new vegetative growth. Does it work?

Brussels sprouts tend to be sweeter if they are harvested after a frost, but they are also susceptible to freeze damage when temperatures reach 14 degrees or so. This makes the ideal window for harvest quite short. A study at University of New Hampshire found that while there were differences across Brussels Sprout varieties, early and midseason cultivars showed increase yields and resulted in higher quality sprouts if they were topped in early September. Topping also reduced the incidence of very small or very large sprouts, resulting in a more uniform harvest. However, if the sprouts had not yet reached marketable size towards the end of the growing season, topping did not effect yields.

Image: Brussels sprouts that were not topped (top) vs. topped (bottom) from the UNH trial. HortTechnology 33, 2; 10.21273/HORTTECH05170-22

While there is limited research on topping tomatoes, it's a common practice among growers. Topping only really makes sense with indeterminate varieties, and growers typically do it ~4 weeks before the final harvest.

Grasshoppers going down

With some spots in the state getting rain, fog, and dew in the last week, we are starting to see some natural control of grasshoppers happen. The drought (this year, and the prior year’s as well) have led to a lot of grasshoppers. This is because in dry weather, the naturally occurring fungus (such as Entomophaga grylli) doesn’t have the moisture it needs to get started. As you harvest and go about end of season tasks, you may see gnarly looking grasshoppers hanging out on the tops of plants – these grasshoppers are likely infected by the fungus, which makes them climb up high to help the fungus spread its spores. This is maybe a little late to help us protect our crops this year, but each infected grasshopper provides a place for the spores to lay in wait to infect grasshoppers next year.

A dead, fungus-infected grasshopper. Photo: Shane Bugeja, UMN Extension

Last chance to apply for soil health equipment grants!

Have you been dreaming of a flail mower to help you deal with residues and cover crops with less tillage? Or maybe a no till seed drill, cultivation equipment that will allow you to reduce tillage for weed management, or something else that will help you to improve soil health on your farm? MDA soil health equipment grants are due tomorrow. The application is very quick and easy, and if awarded, the grant will cover up to 50% of the costs of soil health equipment. Check out the program here.

Has this newsletter helped you this growing season? Let us know!

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