Impact - A new Corn Herbicide for Ontario

A new active ingredient for weed control in corn enters the Ontario marketplace in 2007. Distributed by BASF, Impact (topramezone) is a non-residual contact herbicide that provides broadleaf weed control and activity on a number of grassy weeds. Growers will be encouraged to tank-mix Impact with Frontier + atrazine for contact and residual control of grass and broadleaf weeds from the 1 to 3 leaf stage of corn.

Recommended Tank-Mix Rates

1. Impact: 15 ml/ac (yes, the rate is that low!) +
2. Frontier: 0.45 L/ac +
3. Aatrex 480: 0.42L/ac +
4. Assist: 12.5 L/1,000 L water +
5. 28% UAN: 12.5 L/1,000 L water

Figure 1 - Weed Control achieved in a field scale trial with Impact + Frontier + atrazine + Assist + 28% UAN in 2006. A 3 X 10 m untreated check (see bottom left hand side of the image) was left in the field to evaluate the level of control.

Mode of Action

Impact is an "HPPD" inhibitor similar to Callisto and Converge.

When to Apply

Impact will only control emerged broadleaf weeds at the 1-8 leaf stage and suppress emerged grassy weeds at the 1-4 leaf stage. Impact alone can be applied up to the 7 leaf stage of corn, but when tank-mixed with Frontier + atrazine can only be applied up to the 3 leaf stage of corn.

Strengths

The tank-mix of Impact + Frontier + atrazine will control emerged annual grasses more effectively than Callisto + Primextra II Magnum when applied postemergence to corn.

Weaknesses/Limitations

• Impact alone or in a tank-mix with Frontier + atrazine does not control velvetleaf.
• Impact does not control perennial weeds.
• Broadleaf weed control will be significantly reduced when the tank-mix of Impact + Frontier + atrazine is applied prior to broadleaf weed emergence.
• Fall panicum control will be reduced if the tank-mix of Impact + Frontier + atrazine is applied prior to its emergence.

Annual Weed Control

In public research trials the tank-mix of Impact + Frontier + atrazine effectively controlled the following common broadleaf and grass weeds.

• Common lamb's-quarters
• Lady's thumb
• Pigweed species
• Wild buckwheat
• Common ragweed
• Barnyard grass
• Yellow foxtail
• Green foxtail
• Witch grass
• Large crabgrass

Perennial Weeds

Impact does not offer control of established perennial weeds.

Control of "Odd Ball" Weeds

A number of Federal Research Permits were conducted by the University of Guelph in 2006 whereby field scale weed control of Impact + Frontier + atrazine was evaluated. The following weeds were documented as being sensitive to this tank-mix, however more trial work is need to substantiate these preliminary results.

• Shepherd's Purse
• Annual sow-thistle
• Broadleaf plantain
• Narrow leafed hawk-s-beard
• Wood sorrel
• Black medick
• Creeping speedwell
• Night flowering catchfly
• Seedling dandelion

Cost

At the time of press, pricing on this tank-mix was not available, although in typical fashion we were told that this tank-mix would be priced "competitively".

Summary

Impact is a new offering for emerged broadleaf weed control in corn but also has a surprising amount of activity on small emerged annual grassy weeds in the 1-4 leaf stage. The tank-mix of Impact with Frontier + atrazine provides broad spectrum contact and residual weed control. To achieve effective broadleaf weed control this tank-mix must be applied after broadleaf weeds have emerged. Control of Fall panicum is improved when applications are made to emerged Fall panicum at the 1-4 leaf stage. This tank-mix should not be used when velvetleaf and perennials are the target weed species.

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