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Palmer amaranth – a weed to watch out for (copy)

February 22, 2018 GMT

This winter while at pesticide trainings I have been sharing information on identifying and managing Palmer amaranth. Palmer amaranth is related to waterhemp and pigweed but is much more aggressive in its growth and has been causing lots of challenges to farmers south and east of here.

I recently ran across some information that Jenny Rees, extension educator in York County, put together that I think is worth sharing regarding research conducted in the Southeastern U.S.

The overall point is that we need to think of Palmer management as a system’s approach. This approach may not be economical for every year, but a system’s approach looks at the long-term benefits as a whole. The keys for Palmer -- or any weed -- are to keep it from germinating and then, once germinated, keep it from seed production. Palmer can continue to germinate throughout the growing season to mid-September. During the growing season, quicker canopy closure and post-herbicide apps with residual are key.


At harvest, management includes seriously considering not running your combine through Palmer patches. Jenny heard farmer success stories in 2016 when farmers didn’t harvest their soybean endrows but did harvest the rest of their fields.

Instead, some chose to disk down endrows with heavy Palmer pressure and planted a wheat or rye cover crop in them. In 2017, it made a big difference in reducing Palmer in those fields. Research shows 99 percent of the Palmer seed going through the combine is still viable; thus we’re just moving it throughout the field and from field to field.

The University of Georgia found they had to hoe the plants 2 inches below the soil surface in order to kill them. An average Palmer plant can produce 500,000 seeds/plant. A system’s approach is considering adding a small grain like wheat back into the system. Or, at least consider wheat/rye as a cover crop to help reduce light interception onto the soil surface in early spring.

We’ve also heard more about tillage in the southern states. Spring tillage doesn’t appear to significantly reduce Palmer germination compared to fall tillage. At least two studies showed that fall inversion tillage followed by cover crop resulted in 85-percent reduction of Palmer the next spring, however this can only be done once as subsequent passes bring up older Palmer seed. This is something that should be looked at as a last resort as we can’t afford to go to widespread plowing for soil loss, soil moisture loss and tillage doesn’t fit some of your systems.


Ultimately, the management keys are to ‘start clean and stay clean’ using burndowns, pre’s, several effective modes of action, keeping the ground covered to reduce light interception and incorporating a small grain and/or cover crop into your system. Hopefully this helps as we think about managing Palmer and why we stress being very aggressive in control if you find any in your fields.

For more information or assistance, people are encouraged to contact Aaron Nygren, extension educator, Nebraska Extension in Colfax County by phone at 402-352-3821, e-mail at anygren2@unl.edu or by visit the croptechcafe.org website for more regional cropping information.