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Don’t Overlook These Corn and Soybean Weeds

April 14, 2017
A image showing weeds on an agronomy blog.

Weeds have the ability to lay dormant in corn and soybean fields during winter months. With the aggressive weed pressure seen in 2016, it’s especially important to prepare for the 2017 season with a plan of action in place. Growers can expect the following weeds to be problematic again this season:

  • Palmer amaranth: This weed produces 10,000 to 100,000 seeds per plant and can grow up to 8 feet tall. It thrives in no-tillage systems because it germinates close to the soil. Growing up to 3” per day, it easily overtakes a crop due to its rapid growth. When scouting, look for hairless, diamond-shaped leaves with stems as long as or longer than the leaf blade, varying in color from green to pink.
  • Waterhemp: Producing up to 1,000,000 seeds per plant, waterhemp typically grows 4’-5’ fall, but can grow up to 12’ at a rate of 1” per day. Pollen from the weed can travel half mile or farther because of its cross pollination. Throughout the season, scout for weeds with glossy, elongated leaves that are hairless with stem colors ranging from light green to dark red.
  • Giant ragweed: This weed can produce more than 5,000 seeds per plant and can grow up to 17’ tall, commonly growing 1’-5’ taller than the crop. Giant ragweed has an initial competitive advantage over crops due to its early emergence and rapid growth rate. Scout for large, serrated leaves with 3 to 5 lobes, and long, coarse, fuzzy stems that branch into multiple leaves.
  • Horseweed (marestail): Producing up to 200,000 highly mobile seeds per plant, this weed can grow 5’-6’ tall at a growth rate of 3” per day. It is one of the first glyphosate-resistant weeds identified in U.S. row crops. Unaffected by crop rotation, horseweed seeds spread rapidly and can germinate year-round, but most often in fall or spring.

Last year, due to unpredictable and inclement weather conditions, many growers waited until post-emergence to apply an herbicide – at that point, many weeds had already reached their full height. Managing aggressive weeds this year requires a two-pass system, including both a pre-emergence and post-emergence herbicide application with multiple effective modes of action.

Learn more about how to manage weeds with Resistance Fighter® program from Syngenta, which provides education, local recommendations and a comprehensive herbicide portfolio to help growers and retailers effectively manage resistant weeds in their area. They can then take the Weed IQ Quiz to boost their weed resistance management knowledge.

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All photos are the property of Syngenta or are used with permission.