MSU Extension

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

We are now coming into our second year of using Roundup Ready sugarbeets in Michigan. For most of us, the use of glyphosate (Roundup) in Roundup Ready sugarbeets has made weed control simpler and more consistent. However, as with any changes in production practices there is still a learning curve to using this technology. Additionally, there will be other challenges for growers who are still growing conventional sugarbeets for which timely weed control will be important.

Precautions need to be taken when growing both Roundup Ready and conventional sugarbeets

Keep good records of which fields are planted to the different sugarbeet varieties. Because some growers have both Roundup Ready and conventional sugarbeet varieties on their farms, fields should be clearly marked so there are no mistakes in herbicide applications. There can’t be a worse feeling than spraying glyphosate (Roundup) on a field that does not contain the Roundup Ready trait. This occurrence was common when Roundup Ready soybean, corn, and cotton were first commercialized. One small mistake can cost several thousands of dollars, so it is important to check, double check, and triple check that you are in the correct field before spraying glyphosate.

Make sure the sprayer is properly cleaned out when switching from spraying glyphosate in Roundup Ready sugarbeets to conventional herbicides (micro-rates or standard splits) in non-Roundup Ready sugarbeets. Without proper cleanout, glyphosate solutions or residues left in the tank will lead to tank-contamination that can cause death to sugarbeets in non-Roundup Ready (conventional) sugarbeet fields.

Be timely with herbicide applications. One of the biggest differences in conventional weed control programs compared with Roundup Ready weed control systems is that conventional herbicides generally need to be sprayed when the weeds are less than a half-inch tall and glyphosate in Roundup Ready sugarbeets can be applied when weeds are much larger. Keeping track of weed sizes by scouting both Roundup Ready and conventional sugarbeet fields is extremely important.

Current recommendations in Roundup Ready sugarbeets

Plant Roundup Ready sugarbeets in a weed-free seedbed.

The first glyphosate application should be made when weeds are two-inches tall, subsequent applications should be made before additional weed flushes exceed four-inches tall. Two to four applications will be needed for season-long weed control.

Glyphosate should be applied at a minimum rate of 0.75 lb ae/A (i.e., 22 fl oz/A Roundup WeatherMax or Roundup PowerMax). Higher rates up to 1.1 lb ae/A (32 fl oz/A Roundup WeatherMax or PowerMax) can be applied to harder-to-control weeds prior to 8-leaf sugarbeet. Table 10 of the 2009 MSU Weed Control Guide for Field Crops contains a listing of glyphosate products that are registered for use in Roundup Ready sugarbeets. This table was up-to-date as of November 16, 2008. However, if the product you would like to use is not listed, make sure it is labeled for use on Roundup Ready (glyphosate-resistant) sugarbeet.

Ammonium sulfate (AMS) at 17 lb/100 gal should always be added to maximize glyphosate performance.

Maximum in crop glyphosate application rates include two applications prior to 8-leaf stage sugarbeets totaling 1.9 lb ae/A and two applications after the 8-leaf stage until 30 days prior to harvest totaling 1.5 lb ae/A.

Dual Magnum or Outlook can be tank-mixed with later glyphosate applications to provide residual control of late-emerging grasses and pigweed. Sugarbeets should have at least 4-true leaves.

Roundup Ready sugarbeets are an excellent weed control asset to Michigan sugarbeet growers. But as we make this transition, keep several of these precautions in mind. It will also be important for growers to be good stewards of the Roundup Ready technology, so its benefits will be sustainable in the future