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C.O.R.N
Newsletter
2009-09
April 14, 2009 -
April 21, 2009
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Reminders on Preplant Burndown Treatments, Including Marestail and Dandelion
by
Mark Loux
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Mid to late April is an ideal time to apply burndown and residual herbicides in much of Ohio, before marestail are very large and far enough in advance of planting to allow safe use of 2,4-D ester (see last weeks C.O.R.N. for more information on 2,4-D use). Burndown applications in April control weeds before winter annuals have produced seed, which helps prevent future infestations.
While it is possible to control small weeds in some no-till fields in late March or early April with mixtures of 2,4-D ester plus a residual herbicide, from this point on most soybean fields will require use of a mixture of glyphosate and 2,4-D ester, or paraquat, 2,4-D ester and metribuzin. Including products that contain chlorimuron (Canopy DF/EX, Valor XLT, and Envive) can substantially improve the activity of these treatments on many broadleaf weeds. Where the interval between herbicide application and soybean planting is too short to allow use of 2,4-D, a mixture of glyphosate plus a chlorimuron-containing herbicide is likely to provide the most effective control of a typical no-till weed population. Products that contain cloransulam (FirstRate, Gangster, Authority First, and Sonic) provide additional help primarily on ragweeds and marestail that are not ALS-resistant, and to a lesser extent, on dandelion.
The use of 2,4-D ester is not necessarily as essential in corn burndown programs, compared with soybeans, due to the effectiveness of atrazine, Basis, and Lumax/Lexar, among other herbicides. Based on OSU research, the most effective burndown treatments for corn include (broadleaf weeds): Lexar or Lumax; glyphosate + atrazine; Basis or Resolve + atrazine; dicamba + atrazine; paraquat + atrazine + 2,4-D ester; and atrazine + glyphosate + Balance or Radius. 2,4-D ester can be added to any of these for improved control of dandelion and other tough weeds. Lexar and Lumax have generally provided the most rapid and effective dandelion control, and the addition of 2,4-D to either of these can result in a greater reduction in population.
In both corn and soybeans, dandelions that regrow following a preplant burndown treatment, and are evident in the crop a month or so later, should be treated with postemergence herbicides for maximum reduction in population. It is possible to apply burndown herbicides too early in the spring for dandelion control, since herbicides will be most effective when the dandelions are actively growing with a few healthy leaves. Most of the state should be at this point, but dandelion in more northern areas may still be too small for most effective control. Application of herbicides during periods of cold weather (several days in a row with near freezing temperatures at night) will reduce their activity on dandelion.
An effective marestail management program ensures that the field is free of marestail at the time of soybean planting, and includes herbicides with residual activity to prevent marestail emergence for a month or so after crop emergence. It also helps to plan for the worst – that the population has resistance to glyphosate and ALS inhibitors, and will be impossible to control after soybean emergence. In OSU research, the most effective control of marestail has occurred from a combination of 2,4-D ester, residual herbicides and either glyphosate or paraquat applied in April, when the marestail is still in the rosette stage or has only an inch or two of stem elongation. The residual herbicide component can consist of primarily ALS inhibitors, but this will less consistently effective than a combination of ALS inhibitor plus an effective rate of Valor, Authority, or metribuzin. So, products such as Valor XLT, Envive, Gangster, or Authority First/Sonic often provide more effective residual control than Canopy, unless the Canopy is supplemented with additional metribuzin. Even when applied in spring, the most effective residual herbicides can fail to completely prevent emergence of marestail after soybean emergence.
Now is the time to scout soybean fields where residual herbicides were applied in the fall, in order to determine whether the fall treatment is still controlling marestail. Where scouting turns up small marestail plants in the field, our conclusion would be that the fall-applied residual herbicide is failing to adequately control marestail, and won’t control marestail that emerge later this spring either. Failure to take corrective action prior to soybean planting is likely to result in a marestail mess sometime after soybeans have emerged. The corrective action needed is a preplant application of 2,4-D ester and more residual herbicide (and glyphosate if the marestail are past the rosette stage), to make sure the crop gets off to a weedfree start and that later—emerging marestail are controlled. Marestail escaping a fall residual herbicide are likely to be ALS-resistant, and the residual applied now should include Valor, metribuzin, or Authority to ensure adequate control.
We have received a few questions about Star of Bethlehem control in no-till fields. This weed is not controlled by glyphosate or 2,4-D, but paraquat has substantial activity on it. Weed scientists at Southern Illinois University published a fact sheet on their research into herbicide activity on star of Bethlehem. This fact sheet is posted on the OSU Weed Science website, http://agcrops.osu.edu/weeds .
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C.O.R.N. is a summary of crop observations, related
information, and appropriate recommendations for Ohio
Crop Producers and Industry. C.O.R.N. is produced by
the Ohio State University Extension Agronomy Team, State
Specialists at The Ohio State University and Ohio Agricultural
Research and Development Center. C.O.R.N. Questions
are directed to State Specialists, Extension Associates,
and Agents associated with Ohio State University Extension
and the Ohio Agricultural Research and Development Center
at The Ohio State University.
Information presented above and where
trade names are used, they are supplied with the understanding
that no discrimination is intended and no endorsement
by Ohio State University Extension is implied. Although
every attempt is made to produce information that is complete,
timely, and accurate, the pesticide user bears responsibility
of consulting the pesticide label and adhering to those
directions.
All educational programs conducted by
Ohio State University Extension are available to clientele
on a nondiscriminatory basis without regard to race,
color, creed, religion, sexual orientation, national
origin, gender, age, disability or Vietnam-era veteran
status.
Issued in furtherance of Cooperative
Extension work, Acts of May 8 and June 30, 1914, in
cooperation with the U.S. Department of Agriculture,
Keith L. Smith, Director, Ohio State University Extension.
TDD # 1 (800)
589-8292 (Ohio only) or (614) 292-1868
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