May 31, 2001

Rain Dampens Postemergence Weed Control

Frequent rains continue to interfere with sugarbeet planting and, in some cases, the timely application of the micro-rate according to Alan Dexter, North Dakota State University and University of Minnesota sugarbeet weed specialist. "Proper timing of the micro-rate is very important since the micro-rate only controls small weeds," says Dexter.

The micro-rate should be applied when the largest sugarbeet plants in the field are in the very early two-leaf stage. This normally occurs between 14 and 21 days after planting.

"If the first application can not be timely, then growers should consider using normal herbicide rates rather than the micro rates," says Dexter. "An oil adjuvant can not be used with normal rates so all the herbicides in the combination must be used at a higher rate as compared to the micro-rate plus oil."

Betamix is normally used at 0.5 pints per acre in the micro-rate up to the four-leaf stage, then from 0.5 to 0.75 pints per acre after that. A normal rate would be 1.5 pints per acre. The micro-rate for UpBeet is 1/8 once per acre while a normal rate is 1/3 ounce per acre. Stinger is used at 1.3 ounces per acre in the micro rate while 3.9 ounces per acre is a normal rate.

"UpBeet and Stinger should still be used even with normal rates of Betanex, Betamix or Progress," notes Dexter. "UpBeet is needed for improved control of pigweed, velvetleaf, mallow, smartweed, wild mustard and non-resistant kochia. Stinger is needed for wild buckwheat, common lambsquarters, smartweed, cocklebur, ragweed, nightshade, Russian thistle and Canada thistle."

Dexter says Canada thistle is widespread this year. Stinger in the micro-rate will suppress Canada thistle. "I would suggest broadcasting over Canada thistle patches rather than band spraying since row crop cultivation is not effective. Also the rate of Stinger in the micro-rate can be increased to 2 to 2.5 fluid ounces per acre for better control. The risk of sugarbeet injury is greater as Stinger rate is increased but the increased risk is justified where Canada thistle is dense."

Postemergence grass herbicides, at a reduced rate, can be combined with the micro-rate treatment according to Dexter. If the broadleaf herbicides are being applied at normal rates, then the grass herbicide should be applied separately to reduce the risk of poor grass control. "The broadleaf herbicides will antagonize the grass herbicides," says Dexter. "Also, an oil adjuvant is needed for best control by the grass herbicides but oil can’t be used with normal rates of the broadleaf herbicides."

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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

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