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large seeded broadleaf weeds

Pyrazole family (15) – Zidua, Anthem

Auxins-synthetic (4)

Curtis Thompson, Extension Agronomy State Leader and Weed Management Specialist
[email protected]

The acetamide products are most effective when applied with atrazine. Several atrazine (5) /acetamide (15) premixes are available and should be used instead of acetamides alone unless atrazine is not allowed. These premixes generally fit into two groups: products with a reduced atrazine rate (1 lb or less / acre) and products with a full atrazine rate (1 to 2 lb/acre). Soil type, soil pH, and organic matter will determine whether the reduced- or full-rate atrazine product is used. In past years, often because of cost, reduced rates of these products were applied to help manage heavy summer annual grass pressure, then followed up with a good postemergence herbicide program. With the increased occurrence of glyphosate- and other herbicide-resistant weeds, it is essential to use the full rates of these products in conjunction with a POST program.

Amino acid derivative family – glyphosate, Roundup, Touchdown, and others

Phenoxy family – 2,4-D, 2,4-DB, MCPA, MCPP, 2,4-DP

Carboxylic acid family – Tordon, Stinger, Remedy, Garlon, Starane, Milestone, Trycera

Pigment Inhibitors

There are several preplant and preemergence residual herbicides available for corn. These herbicide programs are key to managing glyphosate-resistant and other difficult-to-control weeds.

Large seeded broadleaf weeds

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The best approach to large-seeded broadleaf weed control in corn is to start clean with a burndown application or a burndown application followed by an application of Acuron® or Acuron Flexi corn herbicide. Both Acuron brands contain multiple, effective modes of actions including bicyclopyrone (group 27), which was developed to complement Callisto® herbicide (group 27) and provides improved control of large-seeded broadleaves.

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Visit or talk to your local Syngenta retailer to learn more.

Cocklebur, giant ragweed and morningglory are often referred to as “large-seeded” broadleaf weeds because they produce larger seeds than their small-seeded counterparts: lambsquarters, marestail and waterhemp. While large-seeded broadleaf weeds tend to produce fewer seeds, the seeds are heartier and often remain viable in the soil for decades. Due to their larger size, the seeds often emerge from deep within the soil profile and present a larger plant mass when they appear, making them more established and difficult to control. To complicate matters, they often appear in flushes, which makes choosing a herbicide with strong residual control a must.

Since large-seeded broadleaves often come in flushes and residual is important to maintain season-long control, we recommend applying Acuron or Acuron Flexi in a 2-pass system: a foundation rate of Acuron or Acuron Flexi followed later by the remaining rate. This approach incorporates multiple, effective modes of action and helps ensure long-lasting residual control.

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

Annual broadleaf weeds can be controlled with preplant-incorporated, preemergence, and postemergence herbicides. The best application method to use depends upon the weed species present and compatibility with your overall production system. This section discusses the various herbicide options.

In addition to proper herbicide selection, timeliness of application and proper application methods are essential. The most common cause of poor results with postemergence herbicides is application when the weeds have grown beyond the optimum size for treatment. As a general rule, postemergence broadleaf herbicides should be applied when weeds are in the two- to four-leaf stage or 2 to 3 inches tall. This normally occurs 2 to 3 weeks after planting.

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Blazer normally causes some soybean leaf crinkling and leaf bronzing or leaf burn. Addition of crop oil concentrate or higher rates of surfactant increase the amount of leaf burn. This injury is temporary and the soybeans recover quickly and grow normally.