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Did Frost Hurt Crops? …A Crop Diagnostic Challenge

University of Minnesota Extension, Stearns County News
May 27, 2015

Source:  Dan Martens, Extension Educator
University of Minnesota Extension
Stearns, Benton & Morrison Counties

Did Frost Hurt Crops? …A Crop Diagnostic Challenge
By Dan Martens, University of Minnesota Extension

FOLEY, Minn. (05/22/15) — Bruce Potter, UM Extension Crop Pest Management Specialist, shared the attached photo with the following comments on May 20:
“I am starting to receive calls and photos of soybeans injured by frost in areas of southwest and central Minnesota. Reports so far are of freeze injury to the crook of soybean plants in the process of emerging. (The crook of these emerging soybean plants has turned brown.)

Injury could vary with residue, topography, planting date; and it sounds like larger soybeans were fine. Plants injured by this way can be killed or severely calloused – depending on the extent of the freeze. Time is needed to evaluate the extent of injury and determine if a replant strategy is needed.”

Then to show how interesting field diagnostic work gets, Bruce followed up later in the day with a note that read:
“Frost may not be the actual (or only culprit in this field). Additional information indicates that this field did have a pre-emerge herbicide (Authority First in this case- could be others) applied as did several other cases.  This injury could be due to Group 14 herbicide injury, in part if not all. At this point, I don't know of any injured fields that did not have a Group 14 Pre-emerge product applied.

“These issues are related to bad timing on the part of soybean emergence and weekend rain followed by growth slowed by cool weather or frost. Soybeans near or beginning to emerge that received significant rain, likely increased herbicide uptake.  This was followed by slow metabolism because of cold weather.  These two types of injury can interact and can be difficult to distinguish.

“For this herbicide injury (as with frost) do not make decisions too quickly.   The survival rate for herbicide injury is probably higher than for frost. Fields with freeze injury do exist.  With current weed problems in MN soybeans, pre-emerge herbicides remain an important tool.”

Then on Thursday morning, while scissors-cut sampling in alfalfa fields, I check some beans that had been planted across the road before the rain. The emerging crook of the soybeans that were peeking through looked black. I sent a picture to Bruce. When I got back to the office, I sliced through the crook with a utility knife. The black color was only skin deep; and was green and firm on the inside. Bruce called and said this was probably a “cold response” and not frost or herbicide injury. With cold conditions, plants are not producing enough chlorophyll to be green. The purple pigments are dominant and accumulate more in some parts of the plant. It can be dark enough to look black.

People who use Internet can search for “Minnesota Extension Crop  News” and find an article related to evaluating frost injury on soybeans, and an article related to frost injury on corn. There are also articles related to evaluating corn and soybean emergence issues.

As Bruce Potter says, It takes time; and within 3-4 days with some warmer weather, you will usually be able to tell whether plants are initiating new growth or not. With a little drier weather any sign of continued growth and development is good. New growth would emerge from the center of corn plants and from buds where leaves join to stems on soybeans. Plants will improve or decline.

Alfalfa seedlings that are showing their first trifoliate leaf are most vulnerable to frost. Here again the key is to watch for signs of damage to seedling leaves and weather new growth continues. It is unlikely that temperature dipped cold enough for long enough to do damage to established alfalfa. Stems might droop, but should recover fairly soon.

You’re welcome call with questions or observations, or for related information. In Stearns County call 255-6169 if a local call to St. Cloud or 1-800-450-6171; in Benton call 968-5077 if a local call to Foley or 800-964-4929; and in Morrison call 632-0161 if a local call to Little Falls or 1-866-401-1111. For Extension Educator Dan Martens, the most direct connection is at Foley.

NOTE: Alfalfa Harvest Alert Scissors-Cut Sampling information can be found now by doing an Internet Search for “Minnesota Extension Crop News.”

Please continue to make SAFETY a priority with spring work and activities.


PHOTO:  Soybean Seedling Frost Injury


Daniel Martens
Extension Educator, Ag Production Systems
(320) 968-5077
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