Features Agronomy Identity Preserved
Evaluating corn growing systems

Will herbicide tolerant corn growing systems take over the market? Probably
not to the same extent as in soybeans.

Over the past five years, Roundup Ready soybean varieties have become the norm,
claiming well over half of all soybean acres. In fact, herbicide tolerance is
cited as the most important variety characteristic – even ahead of yield.
In the US, estimates suggest over 80 percent of all soybean acres are Roundup
Ready. In Canada, that number is about 55 percent.

Growers in Canada currently have access to three different herbicide tolerant
corn systems: LibertyLink, Roundup Ready and Clearfield, with the first two
far and away the most popular. Current estimates suggest Roundup Ready corn
acreage at 13 to 15 percent of the corn crop in Ontario in 2004. LibertyLink
corn acreage is pegged at just over eight percent.

"Both LibertyLink and Roundup Ready corn have excellent tolerance and
are another good weed management option for growers," says Peter Sikkema,
an assistant professor of field crop weed management at the Ridgetown campus
of the University of Guelph. "I believe growers should carefully select
where they will use herbicide tolerant corn." Herbicide tolerant corn should
be used where it will provide excellent weed control and provide the greatest
economic return for the producer.

Weighing the options
Sikkema's take on using herbicide tolerant corn growing systems is clear. For
fields with increasing populations of sowthistle, Canada thistle, wirestem muhly,
quackgrass, horsenettle, ground cherry and other perennials, Roundup Ready makes
a lot of sense.

For fields where Roundup Ready soybeans were grown the year previously, LibertyLink
hybrids are a good fit to avoid using glyphosate two years in a row. LibertyLink
programs should also be considered in fields where increasing populations of
annual weeds exist. "Liberty is strictly a post-emergence contact herbicide
so it doesn't get into root structures of perennials," says Sikkema.

"If you have mostly annual weeds, you'll be happy with the control Liberty
provides. It also does a good job on some perennials, such as wire-stemmed muhly."
In many cases, LibertyLink hybrids also bring European corn borer resistance.
Using one of the LibertyLink programs, either a split application or a tank-mix
with a residual partner like atrazine, provided excellent weed control in Sikkema's
trials.