Volume
6 Issue 6
June 30, 2009
Weed Control in Roundup Ready Sugarbeet
For those
growers unable to apply glyphosate to Roundup Ready sugarbeet
for the first time due to wet soil conditions, apply the maximum
rate of glyphosate allowed. The maximum glyphosate rate for
Roundup Ready sugarbeet is 1.125 pounds acid equivalent per acre
(lbs ae/A). This equates to 32 fluid ounces per acre (fl oz/A)
of Roundup-branded products, 48 fl oz/A of 3.0 pounds acid
equivalent per gallon (lbs ae/gal) products, and 39 fl oz/A of
3.7 lbs ae/gal products. This glyphosate rate can only be
applied up to the eight-leaf stage of sugarbeet. This rate
should be applied to any field with weeds greater than two to
three inches in height or with difficult to control species such
as wild buckwheat, lambsquarters, and common and giant ragweed.
The timing of
sequential glyphosate applications should be based upon weed
density and height and whether individual plants survived the
initial application. Generally, sequential applications should
be applied 18 to 30 days after the preceding application. The
greater the weed density the sooner glyphosate should be applied
sequentially. Once weeds reach three inches in height,
regardless of weed density, glyphosate should be applied a
second time. If plants survived the initial application of
glyphosate, apply glyphosate at the highest legal amount 14 to
21 days later, regardless of weed density and height. Once
sugarbeet has developed beyond the eight-leaf stage, glyphosate
can only be applied at 0.75 lb ae/A. This is equivalent to 22
fl oz/A of Roundup-branded products, 32 fl oz/A of 3.0 lbs ae/gal
products, and 26 fl oz/A of 3.7 lbs ae/gal products.
If common or
giant ragweed have survived the initial glyphosate application,
clopyralid can be mixed with glyphosate at a rate of 4.0 fl
oz/A. This rate of clopyralid will not control all ragweed
plants in the population, but should keep the ragweed from
competing with the crop, unless high densities are present. If
other weed species, not susceptible to clopyralid, survive a
glyphosate application in Roundup Ready sugarbeet, one option is
to continue to apply the highest legal rate of glyphosate in
subsequent applications. The only other option is to cultivate
and remove any remaining surviving plants by hand.
Dr. Jeff
Stachler
U of MN Extension / NDSU Extension
Sugar beet Weed Scientist
