Weeds to Watch: Giant Ragweed
Giant ragweed, if left uncontrolled, can grow up to 15 feet in fertile moist soil. Its rapid emergence and fierce competitiveness make it one of the most difficult weeds in U.S. corn and soybean fields. In Kansas, Indiana, Ohio and most recently Minnesota and Tennessee, growers are facing the addition of glyphosate-resistant giant ragweed to threaten yields. Below are a few characteristics to take note of.
1. Giant ragweed can significantly reduce yield
According to the University of Illinois, season-long competition from a population of two plants per square meter can reduce corn yields by 37 percent, and a population of just one plant per square meter can reduce soybean yields by 52 percent. In Ohio, a single giant ragweed plant every 3 feet of row caused approximately 65 percent yield loss in corn and 80 percent in soybeans.
2. Large seed increases germination success
Germination for giant ragweed starts in late March before the crop emerges and continues through July. The seed has the ability to germinate at considerable depths and, as of recently, emerge later in the growing season, escaping soil-applied herbicides. The large seeds provide more energy reserves for seedlings, making it a more resilient weed.
3. Size limits seed distribution, but traits can be carried in pollen
Movement of seeds is limited, and it therefore becomes increasingly important for growers to manage problems in their own fields. However, glyphosate resistance can be carried through pollen. Therefore, excellent control of “receptor” plants is crucial in weed resistance management.
Purdue University and The Ohio State University offer their recommendations on giant ragweed management in soybeans in this bulletin. These same practices can also be applied to other row crops.
For more information:
· Management of Giant Ragweed in Roundup Ready Soybean Fields with a History of Poor Control
· Glyphosate-Resistant Giant Ragweed: Challenges and Solutions