Palmer amaranth update

March 25, 2016 6:10 PM
Blog Post

Meaghan and Bob’s blog posts on weeds, and seeing a floater spraying yellow herbicide in 30 mph winds on Monday, reminded me to do an update on our newest problem child in the weeds world, Palmer amaranth. While we hoped that the few infestations scattered across Iowa could be contained, unfortunately a few weeks ago I found out that—in Harrison County anyway—Palmer has increased its range and seed bank.

A local agronomist and I were asked to hike out to a “weedy patch” around a mile or so from the original palmer field that is southwest of Modale. In an unharvested area, there were hundreds of Palmer plants, some nearly 6 feet tall; a lot of seed had been produced and scattered. There was also evidence of Palmer in areas of the harvested part of the field, meaning some seed likely went through the harvest equipment. More hiking led to finding Palmer in areas to the west and south of this field. We also found some in an adjoining cornstalk field, so there is potential that palmer seed contaminated that harvest equipment and grain as well.

A few points:

* Palmer is spreading slowly, but this new find and some of the variables with the weed seed being transported off the farm on equipment and in grain means we need to continue to watch and scout for Palmer amaranth, especially in western Iowa.

* Growers are doing a good job watching for this weed (a concerned grower led us to this new palmer field). At winter meetings I had quite a few growers asking to see what a Palmer seed head looks like; some said they need to go look at something similar in their field borders, terraces, and grass waterways. Nice work, keep watching and stay vigilant in scouting for Palmer!

* This spring and summer, scout for palmer amaranth and waterhemp in your fields. Use effective herbicide groups and application rates of residual herbicides. Hit your weeds early with post herbicides. Then scout some more. If you have a few survivors that may be Palmer escapes, contact your local agronomist for help with identification.

*Identification and management information for Palmer amaranth and other weeds:

*The Palmer plant pictured is around 5' tall. I'll let Meaghan and Bob estimate how much seed it may have produced; my guess... a lot.


Clarke McGrath On-Farm Research and Extension Coordinator - Iowa Soybean Research Center

Clarke McGrath currently serves as the On-Farm Research and Extension Coordinator.

Prior to joining Iowa State University, McGrath spent nearly a decade as a retail agronomist and manager in the GROWMARK system, earni...