Monday, June 8, 2015

Postemergence Weed Control Strategies in Sugarbeet

Tom Peters, Extension Sugarbeet Agronomist, Univ of Minnesota / North Dakota State University

Sugarbeet are actively growing following ample precipitation the past three weeks and finally some sun and heat. Unfortunately for Farmers, so are the weeds. Farmers should be scouting their fields and preparing for postemergence weed control. With this in mind, I offer the following suggestions:

  • Scout fields regularly. I suggest visiting fields at least every 7 days
  • Properly identify weeds. Get help if you are unsure about weed identification
  • Spray weeds when they are small, preferably less than 2 inches tall
  • Use full rates of herbicides and the appropriate adjuvants depending on herbicide or herbicide mixtures
  • Consider tank-mixes to provide multiple modes of action, especially on tough-to-control weeds
  • Revisit fields for possible sequential herbicide applications

One year ago, I wrote that farmers should save glyphosate for sugarbeet fields and use other herbicides in corn and soybean fields. I stated in meetings “save your glyphosate chip for sugarbeet fields.” I believed that selection pressure from repeated use of glyphosate in the field across crops grown in the sequence was attributing to the shift from glyphosate susceptible to glyphosate resistant biotypes. And other weed scientists were articulating similar messages; diversifying weeds management by using herbicides with multiple mechanisms of action (MOAs) was recommended by universities to improve the control of tough weeds and slow the spread of resistant weeds. MOA refers to the biochemical interaction that affects or disrupts the target site in weeds. Two common approaches for diversifying MOAs include rotating herbicides in the field across years or using a mixture of herbicides in the tank mixture in the field in the year.

Recently published research by weed scientists from the University of Illinois confirmed management practices are the ‘driving force’ behind herbicide resistance and suggest the herbicide mixture, as opposed to herbicide rotation, is the most effective tool in managing resistance. These researchers studied farm records from over 100 farms in central Illinois, representing almost 500 site years of records from years 2004 to 2010. Their findings indicated that unacceptable weed control was attributed to repeated use of a single herbicide, in many cases, glyphosate, in over 75% of the field/years. Farmers using multiple MOAs in a single application within a field/year were less likely to have product performance concerns or develop weed resistance. However, for the strategy to work, all herbicides in the mixture must be effective on the weed in question.

I am adapting the concept to my recommendations and encouraging farmers use glyphosate in a program approach. For example, begin with preemergence or lay-by herbicides since these count towards the herbicide mixture strategy. Second, I encouraging farmers use a tank mixture partner with glyphosate to control tough weeds in sugarbeet. Which herbicide(s) selected will be dependent on weed pressure in field. For example, use either ethofumesate (Nortron), and UpBeet or Betamix for control of waterhemp. Use Stinger and either ethofumesate, UpBeet or Betamix for control of common and giant ragweed. Any combination of ethofumesate, UpBeet, Stinger or Betamix should be effective for lambsquarters or redroot pigweed control in sugarbeet. Talk to your Agriculturalist or your Ag Retailer about the correct adjuvant to use with glyphosate and tank mix partners.