SW MN IPM Stuff 2016 Issue 5

Volume 19, Issue 5 - May 16, 2016

This newsletter is available in a print-friendly pdf format: SW MN IPM Stuff 2016-05

This newsletter and the advice herein are free. You usually get what you pay for.

Crop Weather

Rainfall, air and soil temperatures, degree-days, soil moistures, and other current and historical weather data for the University Southwest Research and Outreach Center (SWROC), a little spot about two miles west of Lamberton, MN can be found at the SWROC weather webpage.

Last week, we received some reports of corn leafing out underground. The rain that delayed field work last week may have helped these out. The sides of some coleoptiles ruptured when they were caught in a crust. Some herbicides can cause similar symptoms of onion leafing. In some fields planted in drier areas, coleoptile tips opened as they received a shot of light in open furrows or cloddy soil. Subsequent rains covered these leaves with soil.


Early Saturday morning and again on Sunday morning, SW MN experienced a frost. Drier soils and lack of wind allowing the cold air to settle made the Sunday event worse in many cases. Here are a few thoughts:


Some have commented on differences in damage for individual plants being frosted. That could be because of uneven emergence, residue, differences in tolerance by hybrid for refuge in a bag, or other factors. 

If planted at a proper depth, the growing point or one to three collar corn is well below-ground and protected from frost. The growing point approaches the soil surface as the plant grows but should be below ground until the 5 to 6 leaf stage.

frost damage

Frost killed the crook on this frosted plant.

Unless frosted corn leaves are trapped in the soil or buggy whipped, and even when they are, the new leaves should emerge just fine. There should not be a large difference in development stage between injured and un-injured corn - unless there was one before the frost. Some of these partially frosted plants are likely to lose some leaves too.

Before getting overly concerned or overconfident, give the corn a few days to allow damage to become fully visible or for new leaves to emerge.

In the photo above, by killing the tissue in the crook, frost might actually help this plant emerge from a crust. These are slightly frosted plants at the UMN SWROC. Other areas of the state saw more damage.

In some parts of Minnesota, the corn in lower, frost-prone areas may have already been thin because of standing water.

frost on corn

Frost damaged leaf with insect feeding.

You might want to give corn and weeds both a couple days after the frost to recover before applying post-emerge herbicide. Let the weed and corn stage, weather forecast and your workload help guide you decisions. Fungicides, tillage, etc. are not likely to help frost damaged corn recover any quicker.

For more information see: Frost injury to corn seedlings unlikely to greatly impact yield.

This frost did, however, make scouting for early-season stand reducing insects tougher.


frost beans

Cotyledon stage soybean that survived the frost.

Cotyledon stage soybeans are more frost tolerant than seedling corn. Unfortunately, their growing point is above ground and not protected by a layer of soil. Unless the plant is killed below the cotyledon you should wait 3-5 days before evaluating frost injury.

You need to wait to see if the axillary buds at the base of the cotyledons grow or have been are killed. Also, plants need time to recover from any herbicide injury related to cold, wet conditions.

Production Agriculture Events at the SWROC

There will be a training for agricultural producers at the U of MN SWROC on Monday, July 11th. Details to follow.

Happy trails,

Bruce Potter