by Dr. Jeff Stachler, Sugar beet Weed Scientist
U of MN Extension / NDSU Extension
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.