Features Agronomy Weeds
Another corn herbicide active

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 one to
three leaf stage of corn.

Recommended tank-mix rates

• Impact: 15mL/ac (yes, the rate is that low!) +
• Frontier: 0.45L/ac +
• Aatrex 480: 0.42L/ac +
• Assist: 12.5L/1000L water +
• 28 percent UAN: 12.5L/1000L water.

Mode of action
Impact is a 'HPPD' inhibitor similar to Callisto and Converge.

When to apply
Impact will only control emerged broadleaf weeds at the one to eight leaf stage
and suppress emerged grassy weeds at the one to four leaf stage. Impact alone
can be applied up to the seven leaf stage of corn, but when tank-mixed with
Frontier + atrazine can only be applied up to the three 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 post-emergence
to corn.

Weaknesses and 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 grassy weeds: common lamb's quarters,
lady's thumb, pigweed species, wild buckwheat, common ragweed, barnyard grass,
yellow foxtail, green foxtail, witch grass and 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 needed to substantiate these preliminary results:
shepherd's purse, annual sowthistle, broadleaf plantain, narrow-leafed hawk's
beard, wood sorrel, black medick, creeping speedwell, night flowering catchfly
and seedling dandelion.

Cost
At press-time, 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 one to four 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 one to four leaf stage. This tank-mix should
not be used when velvetleaf and perennials are the target weed species.

Allan Kaastra, MSc. Candidate, University
of Guelph; and Mike Cowbrough, OMAFRA, Guelph.