Can a cereal rye cover crop effectively suppress giant ragweed?

giant ragweed
cover crop

Chudzik, Arneson & Werle


March 4, 2023

As growers across the Upper Midwest continue to adopt cereal rye cover crop and/or plant their soybean crop earlier in the season, research investigating how these agronomic decisions influence weed communities and best management practices is warranted.

According to our stakeholder surveys, giant ragweed (Ambrosia trifida), an early-emerging and competitive species, is among the most troublesome weeds in soybean cropping systems across the Upper Midwest (Figure 1).

Figure 1. Giant ragweed seedling.

In Wisconsin, giant ragweed populations with extended emergence pattern (from April through late June/early July) are common (Figure 2).

Figure 2. Giant ragweed emergence pattern in a soybean weed management study conducted in 2018 and 2019 at the Rock County Farm, Janesville, WI (Striegel et al [2021]).

Thus, a field study was conducted in 2021 and 2022 at the Rock County Farm, Janesville, WI to evaluate the impact of soil and cereal rye cover crop management practices, soybean planting time, and PRE-emergence herbicide application on giant ragweed management in soybean.

Figure 3. WiscWeeds team establishing weed management trials at the Rock County Farm, Janesville, WI.

Our Integrated Giant Ragweed Management Study Consisted of:

To simulate common practices adopted by soybean growers, Enlist One @ 2 pts/acre + Roundup PowerMax @ 32 fl oz/acre (2,4-D-choline [Group 4] + glyphosate [Group 9]) were applied POST-emergence when ~50% of giant ragweed plants within a treatment reached ~4 inches in height.

Preliminary Results:

Figure 4. Tillage treatment in late planted soybean. First POST-emergence application was required 20 days after soybean planting (06/21/2022). Picture taken by Guilherme Chudzik on 06/14/2022.

Figure 5. Planting green treatment in late planted soybean. First POST-emergence application was required 28 days after soybean planting (06/29/2022). Picture taken by Guilherme Chudzik on 06/14/2022.

Impact of Cereal Rye Cover Crop on Giant Ragweed Establishment:

Figure 6. 2022 research plots with different levels of cereal rye cover crop biomass (Rock County Farm, Janesville, WI).

Both of these studies will be replicated in 2023 to validate the results observed during the 2021 and 2022 growing seasons. Thus, stay tuned for plot tours and additional information from these studies during the 2023 growing season!

Given the nature and biology of giant ragweed in Wisconsin, tillage and/or effective chemical burndown to eliminate established plants at the time of crop establishment and effective POST-emergence programs (foliar control) are necessary management practices. Remember that giant ragweed seed has short viability in the soil seedbank (most giant ragweed seeds die after 2 years in the soil). Thus, after a couple years of intensive management (no giant ragweed escapes producing new seed), giant ragweed infestations should become minimal. Check this giant ragweed article for additional information.

The research reported herein is being led by Guilherme Chudzik (WiscWeeds MS student). Click here to see Chudzik’s poster presented during the 2022 North Central Weed Science Society Meetings (December 2022) in St. Louis, MO. Chudzik received a NCWSS Graduate Student Travel award to attend the 2022 conference and present his MS research (congrats Guilherme!).

Additional resources:

This article was written by Guilherme Chudzik (MS Student), Nick Arneson (Outreach Program Manager), and Rodrigo Werle (Assistant Professor). All authors are affiliated with UW-Madison.

Thanks to the WiscWeeds team and Rock County Farm staff for assisting this research.