Postemergence
Herbicide Injury
Chris
Boerboom
As we shift into the season for
postemergence corn herbicide applications, we need to remember a
few basic precautions to reduce the risk of herbicide injury.
From the calls that I receive, the three main reasons for
herbicide injury are improper time of application, tank
contamination, and drift. In terms of timing, late applications
generally increase the risk of injury. Review the list of height
or stage restrictions for postemergence herbicides and make sure
applications are made on time (Table 1). Remember, the
preemergence grass herbicides (Dual II Magnum, Frontier,
Harness/Surpass/TopNotch, Micro-tech/Partner, and Prowl) listed
in the table will not control emerged grasses, but will provide
residual grass control when applied postemergence.
For tank contamination, be
especially careful to make sure glyphosate products (Roundup,
Touchdown, etc.) are completely flushed from a sprayer before
treating any non-Roundup Ready hybrid. Even a small amount of
glyphosate spray in a sprayer’s sump can contaminate the next
spray load. Contamination with ACCase inhibitors (Assure, Poast,
etc.) can be equally damaging as glyphosate to corn. I may have
a half step less concern with Lightning, Pursuit, and Raptor on
non-Clearfield corn, but care needs to be taken with these
herbicides as well.
Drift management also needs to be
a concern. With more postemergence applications being made, the
risk of off-site damage increases compared to preemergence
applications. This is logical because postemergence herbicides
have postemergence activity whereas many preemergence have
limited or no postemergence activity. Wind speed and if the wind
is blowing in the direction of sensitive site (eg.
housing) or sensitive crop are two of the most important factors
that you need to consider to manage drift. Then, you need to
assess the risk of drift. Drift management depends on your
assessment and subsequent decisions. With more organic growers
in the state, it is also wise to know where their fields are and
take special precautions to avoid drift toward their fields.
I have not received many calls on
fields sprayed with the wrong herbicide for the type of corn
hybrid planted (eg. a field sprayed with Roundup that wasn’t
Roundup Ready) because the mistakes is quite obvious when it
happens. Still, I know that these mistakes are happening on rare
occasion. Double check spray requests with herbicide resistant
corn for hybrid type, herbicide, and field location. It’s easy
to mis-speak and switch Lightning for Liberty or vise versa. |
