Weeds Waking Up: Giant Ragweed
The emergence sequence of weeds can help with weed management decisions by knowing at what point in the planting and growing cycle to expect them. Giant ragweed, next in our Weeds Waking Up series, emerges several weeks prior to corn planting.
Giant ragweed is a large-seeded broadleaf weed that lives up to its name. It grows fast and can reach colossal heights of up to 20‘, pilfering water, nutrients and sunlight from surrounding corn and soybean plants as it grows. Its height and voracious appetite for resources aside, giant ragweed – like other large-seeded broadleaf weeds – is difficult to control because its seeds germinate deep within the soil profile where they are shielded from herbicide applications.
While herbicide active ingredients are easily applied to weed seeds on or near the soil surface, they may not always reach deeper seeds or reach them at reduced rates. To complicate matters, the deeper germination depth means giant ragweed emerges with more plant mass, making it harder to control with post-emergence herbicide applications.
Giant ragweed facts:
- Can produce more than 5,000 seeds per plant.
- Is often 1 to 5’ taller than the crop with which it is competing.
- Season-long competition from just 2 giant ragweed plants per 110 square feet can reduce corn yield by up to 13%.
Learn how to identify and manage giant ragweed in this video with Joe Wuerffel, global technical manager in weed control for Syngenta.
Syngenta recommends controlling giant ragweed with Acuron® or Acuron Flexi corn herbicides. Acuron has 4 active ingredients and 3 effective sites of action (Groups 5, 15 and 27), and Acuron Flexi has 3 active ingredients and 2 effective sites of action (Groups 15 and 27). Both herbicides contain the active ingredient bicyclopyrone (Group 27), which was developed to complement Callisto® herbicide (Group 27) and provide improved control of large-seeded broadleaf weeds like giant ragweed.
For soybeans, a pre-emergence herbicide applied prior to the weed reaching 4’’ in height is recommended. A post-emergence herbicide, such as Flexstar® GT 3.5 that delivers 2 different sites of action (Groups 9 and 14), can help manage glyphosate- and ALS-resistant giant ragweed.
Backed by decades of research and development, Syngenta has been at the forefront of introducing herbicides with multiple effective sites of action to help fight resistance. The Syngenta Resistance Fighter® program provides education, local recommendations, and a comprehensive herbicide portfolio to help growers and retailers effectively manage resistant weeds in their area.
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