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Posted 26 March 2015. PMN Crop News.

Answering the Threat of Waterhemp

Tillage among suggestions for managing oft-germinating weed

Source: United Soybean Board Press Release.

Chesterfield, Missouri (March 10, 2015)--Waterhemp is among the most problematic pigweed varieties for soybean farmers in the United States. The weed has been identified as resistant to six herbicide modes of action, and resistant plants have been found in 16 different states. Similar to its cousin, Palmer amaranth, waterhemp is a pigweed variety that can germinate quickly over a wider range of conditions than other weed species.


“What makes waterhemp very problematic in our soybean-production system is that it has a discontinuous germination pattern,” explains Kevin Bradley, an associate professor at the University of Missouri. “This means it has multiple seedling flushes throughout the summer. And albeit rare, (it) can even germinate after harvest.”

Bradley offered suggestions to deal with herbicide-resistant waterhemp during a recent Focus on Soybean webinar, Waterhemp Management in Soybean. Those suggestions include:

1. If possible, use tillage to bury the weed’s seed bank. Waterhemp seeds will not grow when six inches or deeper in the ground. Of course, Bradley cautions against using tillage in regions with soil-erosion concerns.

2. Use full rates of herbicides, and mix them. Relying on any one herbicide alone will only build up the weed’s resistance to it. Apply both pre-emergence and post-emergence herbicides with residuals in a full-fledged effort against weeds.

3. Learn as much as you can about waterhemp and other weed species growing in your area. The United Soybean Board’s Take Action program offers a weed identification guide to help.

Farmers can fight herbicide-resistant waterhemp with a well-planned and diverse weed-management strategy. Learn more about herbicide resistance, how to integrate more modes of action into your weed-management plan and explore other resources at