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OSU Extension, Darke County...
Fall Weed Management
By Justin Petrosino, ANR Extension Educator
There are rumors around Darke County that a few corn fields are
shelled. Corn fields around Urbana and Springfield that were planted
early, early being a relative term this year, are also harvested. At
Farm Science Review yields are averaging 170 bushels to the acre. For
most of us harvest is still a few weeks out and 170 bushels would be a
blessing. In the meantime it may be pertinent to think ahead for
some options for fall weed management. Once the crops are off fall is a
great time to manage weeds like marestail, volunteer wheat, and a host
of biennials and perennials.
The first step to a strong weed management program is to determine what
weeds are present. Scouting a field is imperative to choose the right
herbicide program. An example would be applying metribuzin + 2,4-D to
control marestail in a field that will be soybeans in 2012. If the
field also suffers from an infestation of dandelions they will not be
controlled. Be sure to properly identify the weeds present and choose
the best program accordingly.
The second step was alluded to in the previous paragraph. Next year’s
crop will determine this fall’s herbicide or vice versa. According to
Dr. Mark Loux, OSU Weed Management Specialist, herbicides like Basis,
simazine, and Autumn will work for ground going into corn if they are
paired with 2,4-D. For soybeans Canopy, metribuzin, and Autumn with
2,4-D will control many winter annuals. If the crop for next year is
undecided glyphosate + 2,4-D is an excellent option. It has excellent
activity on most winter annuals and perennials without having residual
activity into the spring.
The third step to a successful program is timing of application.
Control of many winter annuals can be achieved much later than most of
us think. Applications made in mid November can be effective. There are
several points to consider to maximize the effectiveness of the control
measure. You must be able to see the weed to control it. Snow cover
will prevent the herbicide from contacting the weed which will prevent
uptake. Avoid applying herbicides after drastic changes in temperature.
Warming and cooling events that change temperatures 10 to 15 degrees
can stress weeds and prevent herbicide uptake. As long as weeds are
visible, green, not under stress, and temperatures are above freezing
weeds can be controlled.
Dr. Loux and the Weed Warriors at OSU have done yeoman’s work when it
comes to researching marestail management. For several years now
Extension has disseminated information on marestail management through
pesticide applicator training, the CORN Newsletter, field days, new
columns, and through personal consultation. The recommendations still
haven’t changed. In the fall emerged marestail needs to be managed with
one of the aforementioned herbicide programs or tillage. In the spring
marestail needs to be controlled with tillage or a strong burndown
containing glyphosate + 2,4-D, Ignite + metribuzin, glyphosate +
Sharpen + MSO, or paraquat + metribuzin + 2,4-D at the appropriate
rate.
A residual herbicide with activity on marestail should be included with
the burndown. A single postemergence application of glyphosate or
glyphosate + an ALS product will not control marestail. Especially
since glyphosate and ALS resistance abounds. Once marestail bolts and
reaches heights above 4 to 6 inches it becomes very hard to control.
Leaving marestail unmanaged, as in a single glyphosate application,
cost 16 bushels in OSU research. Planning ahead this fall and into the
spring can help save 16 bushels. In today’s prices that is $210, not a
bad investment at all. For more information on marestail management
visit http://agcrops.osu.edu or obtain a copy of the Weed Control Guide
from the Extension
Office.
Last fall dry conditions persisted and held back much of the weed
pressure. In September and October very little marestail emerged.
Therefore a herbicide application or tillage may not have benefitted
the field. This year conditions appear to be damper and with all of the
uncontrolled marestail from poor spring management seed will abound.
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