Rainy Days Offer Opportunity to Chop Down and Control Weeds


Andrea Johnson, Minnesota Farm Guide


MORRIS, Minn. – The growing season of 2017 produced very large weeds.

In west central Minnesota, the rain total was less than 12 inches from March through July, followed by over 8 inches of rain in August, almost 3 inches of rain in September and more than 2 inches during the first week of October.

The weeds thrived in dry conditions followed by the normal to wet conditions.

If farmers are waiting to begin harvest because of rain and conditions are correct for a herbicide application, October is a good time to control perennial weeds, like Canada thistle or dandelion. The weeds are moving nutrients into their roots and this provides an opportunity to use herbicides for control, suggested Jared Goplen , University of Minnesota Extension educator in crops, based out of the West Central Research and Outreach Center, in Morris.

For annuals, large seed heads are easily visible for cutting down and destroying, he added. The soybeans and corn have turned brown, but many of the weeds have maintained their green color.

“It makes it a little bit easier to walk those soybean fields, to go out and hand weed and drag some of those weeds out of the fields,” he said. “It’s a lot of work, but you are getting the seed out of the field and preventing further problems for next year.”

Goplen said waterhemp has been prolific in southwest Minnesota and the west central part of the state this year.

Giant ragweed has been the largest concern in south central and southeast Minnesota. Up in the northwest, common ragweed is the main weed.

“Certainly, in all those areas you have some other pigweed species – like redroot pigweed and lambsquarters,” he said.

Using a weed identification book or just checking weed identification with a cell phone and Internet is helpful.

“Once you train your eye, it becomes a lot easier to identify some of those,” he said.

When differentiating between pigweeds, each type has its own seed head structure.

A lack of hairs on the stems are indications of Palmer amaranth or waterhemp, and both have both male and female plants. The rest of the pigweeds have the male and female flowers on the same plant.

There have been no additional sightings of Palmer in Minnesota in 2017, after the weed was found in 13-14 conservation plantings in western Minnesota in 2016. The Minnesota Department of Agriculture has overseen destruction of Palmer in the conservation plots both in 2016 and throughout this growing season. The plots were aerial sprayed with Milestone herbicide early this summer, and propane torches and spot herbicide applications were also used to destroy any weed seedlings and prevent seed production from occurring.

Goplen would like people to remember if they have weeds on the edge of the field, it’s pretty easy when harvesting soybeans or corn to pull those weeds into the combine, which is the easiest way to spread weed seeds across a field. Taking a moment to cut down those weeds now could save time when harvest begins. It could also reduce the weed seed population in the field.

“Especially thinking about those field edges, pulling back a row or two if they are real weedy, can prevent some of those weeds from being spread into the middle of the field,” Goplen said.