Mark Renz UW Madison Associate Professor and Extension Specialist, Sam Marquardt UW Madison Assistant Outreach Specialist
Pigweeds aren’t going away anytime soon. In fact, Palmer amaranth and waterhemp are moving into new areas of Wisconsin where they previously did not exist.
We recently posted a new video that demonstrates how to differentiate flowering pigweed species. This video will display easy to spot differences in the male and female flowering structures of different pigweeds including: redroot pigweed, smooth pigweed, waterhemp, and Palmer amaranth.
While it is relatively easy to identify these species while in flower, realize that if you intend to control plants it is much more desirable to identify it when plants are young and vegetative (e.g. < 6 inches tall). A range of methods are available that are effective at controlling the plants and preventing seed production at this stage. Few options for effective control exist once plants are taller than this, especially when they are flowering.
As most people know, Palmer and waterhemp have been found to be really good at developing resistance to a range of herbicides. While many reasons exist for this like their dioecious nature and producing many seeds (Palmer can have up to 2 million seeds per plant) we need to try to limit the spread of these plants in Wisconsin. Unfortunately, we also need to realize that we don’t have control of all of the pathways that may result in new infestations in Wisconsin.
We need to keep a vigilant eye out for new populations and eradicate them before they establish a large seedbank and impact our agronomic fields. To do this we need to become effective at identifying these different species. Previous resources created this year include:
If you find a new population of palmer amaranth or waterhemp, please report it! Follow this link to the Report a Pigweed page on the Wisconsin First Detector Network website to learn more about pigweeds and how to report them or email us directly at reportapigweed@gmail.com.