May 22, 2003

 

Rain Delays Postemergence Herbicide Applications on Sugarbeets

Timely application of postemergence herbicides is important for good weed control in sugarbeets, especially with micro-rate applications according to Alan Dexter, North Dakota State University and University of Minnesota sugarbeet weed specialist. "Widespread rain over the past few weeks has made timeliness difficult and switching from micro-rates to conventional rates may be necessary in some fields.

Tank mixing pesticides for various purposes can save trips over the field. Growers have recently reported areas of cutworms and are inquiring if an insecticide for cutworms can be tank-mixed with herbicides. "It depends," says Dexter.

"Insecticide formulations sometimes act as adjuvants and increase the activity of postemergence sugarbeet herbicides so insecticides should not be applied in combination with conventional rates of herbicides. The micro-rate treatments already include an oil adjuvant so adding an insecticide will have no further effect. So the answer is yes for insecticides plus the micro rate but no for insecticides plus conventional rates of herbicides."

Many sugarbeet producers are using a cover crop to reduce erosion and protect small sugarbeet plants from wind damage. However a cover crop, like weeds, can compete with sugarbeets so early control is important to prevent yield loss.

A small grain cover crop growing close to the sugarbeet row should be controlled when it reaches the three-leaf stage. A band sprayer could be used to control the cover crop which would leave live cover between the rows for added protection, according to Dexter. "Cover crop between the row should be controlled when it reaches the five-leaf stage. Growers should also remember that dead and dying small grain plants will continue to protect against wind damage for some time after a herbicide treatment. Row crop cultivation should be delayed as long as is reasonable when considering the need to cultivate for other weed problems."

Dual Magnum, Outlook and Treflan are all registered for lay-by application. Treflan is the least expensive according to Dexter but must be incorporated for best activity. Treflan can cause severe sugarbeet injury if a long period of wet weather follows application.

Dual and Outlook do not need to be incorporated but rain is necessary for activation. "Sugarbeet injury from Dual and Outlook is possible but delaying application until the four-leaf stage will greatly reduce the risk," Dexter says. "Weed control from lay-by Dual and Outlook largely depends on rainfall after application."

Using Quadris, a fungicide, plus postemergence herbicides is not recommended because it has caused severe sugarbeet injury according to Dexter.

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Source: Alan Dexter, (701) 231-8131, adexter@ndsuext.nodak.edu
Editor: Rich Mattern, (701) 231-6136, richard.mattern@ndsu.nodak.edu