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Palmer amaranth in soybeans. Photo by OSU Extension.

Watch for Palmer amaranth during harvest

The perch from the combine this fall offers a great view for catching breakouts of Palmer amaranth and other problem weeds in fields.

Ohio State university weed control specialist Mark Loux is still emphasizing the importance of spotting problem weeds before they take over a field.

“Keep an eye out for waterhemp and Palmer amaranth when harvesting, with the goal of preventing further spread if found. Where plants or patches of these are encountered, think twice about just harvesting right through them,” Loux said. “Doing so will disperse seed more widely throughout the field being harvested and also contaminate combines with the possibility then of spread to other fields. We have seen all of this occur in our investigations of Palmer amaranth. The wiser choice where these weeds are encountered, or where additional help with identification is needed: avoid harvesting through the weeds for now, get positive identification, and remove them by hand prior to harvesting the crop in that area.”

Palmer amaranth emergence begins in May and lasts through the fall, said Seed Consultant, Inc. agronomist Matt Hutcheson. The weed has a prolific growth habit and resistance to multiple herbicide modes of action, making it is critical to identify and control Palmer amaranth.

It can be easily confused with other pigweed species. It is important for growers to have the ability to identify Palmer amaranth so that it is not confused with other pigweed species. There are a number of useful universities resources for ID and control of Palmer, including: http://u.osu.edu/osuweeds/super-weeds/palmer-amaranth/.

Hutcheson offers the following tips for controlling Palmer amaranth in the future.

‪1. Scout for and identify problem weeds early. Palmer Amaranth is a pigweed species and can easily be confused with other pigweeds, such as redroot pigweed, during early growth stages. It is critical to identify weeds correctly in order to keep them from spreading. Universities such as Ohio State, Purdue, and Michigan State have excellent fact sheets with pictures to aid in weed identification.

‪2. Start with a weed-free seedbed. Effective burndowns or deep tillage will help control Palmer Amaranth and will allow growers to begin the season with a weed-free seedbed. Apply herbicides when the seedlings are less than four inches tall.

‪3. Use residual herbicides. Use of residual herbicides will control seedlings at emergence and limit the number of plants that will need to be controlled by post-emergence applications. This is especially critical in soybean fields, where effective post-emergence options are very limited

‪4. Crop rotation from soybeans to corn will allow for the use of additional herbicide modes of action (herbicides used in corn) that are effective at controlling Palmer amaranth.

‪5. Consider hand weeding if plants escape normal management practices. Removal before they produce seeds is essential. If a seed head has formed, place a trash bag over the seed head before removing the plant from the field to eliminate the spread of seeds across the field.

‪6. Manage drainage ditches, field borders, etc. Regularly mowing ditches, waterways, field borders, etc. will help control the spread of this weed. Although weeds growing in ditches do not directly compete with field crops, they will produce seeds and promote the spread of Palmer amaranth.


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