Pennsylvania: Palmer Amaranth and Waterhemp Beginning to Emerge

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Pigweed species have begun emerging for the season in Pennsylvania, including reports of Palmer amaranth and waterhemp in southeastern Pennsylvania. It is important to scout for these invasive weeds now, and control them before they reach 4 inches tall.

Palmer amaranth and waterhemp are highly competitive pigweed species with widespread herbicide resistance that continue to spread through Pennsylvania. They are confirmed on over 40 farms across the state, with the highest concentrations in southeastern counties. While their emergence was delayed this year due to cool May temperatures, pigweeds have now begun emerging in Pennsylvania.

Now is the time to scout fields for Palmer amaranth and waterhemp, in order to control them with effective herbicides before they reach 4 inches tall. Because of widespread resistance to glyphosate (Roundup) and the Group 2 herbicides (ALS-inhibitors), herbicide programs should include multiple other effective modes of action.

Very young Palmer amaranth and waterhemp may be identified by carefully examining their stems and leaves. We have compiled many resources onto a website including identification, management, and timely updates on these pigweeds. Please refer to this website for in depth information on the best management practices for these weeds.

This includes a 5-part video series on identification and management, identification photos, and a one-page flier that highlights some key points about these species. As new and more information is acquired, we will post them on this website. The Integrated Weed Management Resource Center also has valuable resource on invasive pigweeds.

Palmer Amaranth
Palmer amaranth – seedling; notched tip, no hairs, broad ovate shaped leaves, no waxy sheen (A. Hager, University of Illinois)
Waterhemp seedling
Waterhemp seedling – egg shaped cotyledons, notched tip, no hairs, narrow lanceolate leaves with waxy sheen (A. Hager, University of Illinois)
Palmer amaranth seedlings emerging
Palmer amaranth emerging in Berks County. Photo taken June 13, 2017