Residual Herbicide Planning

In many situations, soil and foliar applied herbicides with residual weed control are primary elements of corn and soybean weed management programs. Burndown and pre-emergence (PRE) herbicides or mixtures with 2 to 3 different herbicide sites of action should provide control of the most prevalent and competitive weeds in each field. This approach will help minimize early season weed competition that has the greatest impact on crop yield potential and help keep weeds small, within label guidelines, so post-emergence applications can be made in a timely fashion. Overlapping residual herbicide programs can help manage late emerging weeds such as waterhemp. Effective weed management plans are predicated on identifying weeds and their competitive impact on crop yield potential and then selecting herbicides and application times to limit weed competition. Timely, in-crop scouting is required to help make adjustments to control tactics, determining the right products and rates for herbicide mixtures and application timing for each weed infestation.

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Table 1
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Most research studies have found that crop yield potential is protected if weeds are controlled before they reach a height of four inches in corn or soybean.3 Corn is very sensitive to early-emerging weed competition and broadleaf weeds tend to be more competitive with corn than grasses (Table 1).

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Residual herbicides should be considered for control of kochia, waterhemp, and common ragweed, as well as other weeds in corn and soybean. Kochia, waterhemp, and common ragweed produce large quantities of seed with high germinability (Figures 1, 2, 3, page 4). Kochia is an early germinating weed, beginning in early March and continuing into May.1,2 Waterhemp begins to germinate in mid-May, with peak emergence in early July. Both species have a high degree of genetic diversity, resulting in numerous biotypes with varying degrees of sensitivity to herbicides.

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Residual herbicides with sites of action in Groups 4, 5, 14, 15, and 27 are effective on most kochia, waterhemp, and common ragweed. This would include: clopyralid or dicamba (4), atrazine (5), sulfentrazone (14), acetochlor (15), and isoxaflutole (27) in corn and metribuzin (5), flumioxazin (14), and acetochlor (15) in soybeans. Check individual product labels to select products that fit a cropping system and weed spectrum. Many residual herbicides may need to be tank-mixed with burndown, foliar, and other residual products for broad-spectrum weed control.

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Visit Roundup Ready PLUS® Crop Management Solutions http://www.RoundupReadyPlus.com/ for product recommendations and additional tools to help make management decisions to protect crop yield potential.