Weed and Insect Resistance A Growing Problem

Weed and Insect Resistance A Growing Problem

January 20, 2015

Weed resistance to herbicides is not a new thing. It began to occur as soon as man started using chemicals for weed control. Back in the mid-1950s, weed scientists predicted that repeated use of any herbicide could lead to shifts in weed species composition within a weed community and that herbicide tolerance in weeds can quickly increase with repeated use of the same herbicide. Soon after that (early 1970s) the first cases of weed resistance occurred in pigweed species showing resistance to atrazine.

Register Now for Weed and Insect Resistance Workshops

Weed and insect resistance pose yield and economic challenges for today's farmers. Learn about the importance of herbicide and insecticide resistance management, mode of action, and how to use the Site of Action Numbering System to reduce the potential for weed resistance in Nebraska.

Workshops will be offered at four locations:

  • Feb. 3 in Fremont
  • Feb. 4 in Nebraska City
  • Feb. 5 in Hastings
  • Feb. 6 in Grant

This four-hour workshop starts with several speaker topics for discussions and then active involvement of attendees. Topics will include:

  • insect resistance
  • herbicide tolerant crops,
  • herbicide mode of action and site of action groupings,
  • how weed resistance develops,
  • weed resistance in Midwest and Nebraska.

There also will be a hands-on exercise on weed control problems.

Workshop speakers are members of the UNL Weed Science and Entomology teams, including: Stevan Knezevic (lead), Amit Jhala, Greg Kruger and Julie Peterson. This workshop is sponsored by an educational grant from the United Soybean Board.

Preregister online. Cost for the workshop is $30. For more information contact host county educator, or myself (sknezevic2@unl.edu), or my secretary, Wendy Winstead (wwinstead2@unl.edu).  


All programs start at 9 a.m. local time.

Feb. 3 — Fremont,  First State Bank and Trust Company, 1005 E 23rd St, Fremont; for more information contact host educator Nathan Mueller, 402-727-2775, nathan.mueller@unl.edu
Feb 4 — Nebraska City, Kimmel Education and Research Center, 5985 G Road; for more information contact host educator Gary Lesoing, 402-274-4755, gary.lesoing@unl.edu
Feb 5 — Hastings, Adams County Fairgrounds, 947 S Baltimore Ave; for more information contact host educator Ron Seymour, 402-461-7209, ron.seymour@unl.edu
Feb 6 — Grant, Perkins County Fairgrounds building, 100 Garfield Ave; for more information call  Kathy Mailend, 308-352-7580, perkins-county@unl.edu, or Strahinja Stepanovic, 402-318-1124, sstepanovic2@unl.edu.

Stevan Knezevic
Extension Weeds Specialist

There is well documented literature about weed resistance. Worldwide about 368 herbicide-resistant weed biotypes reported to be resistant to 19 herbicide modes of action. For example, 40 dicot and 15 monocot species are known to have biotypes resistant to triazine herbicides. Also, at least 50 weed species have been reported to have biotypes resistant to one or more herbicide families (www.weedscience.com). Repeated use of the same herbicide was always the main reason for weed resistance to herbicides worldwide.

Insects have shown a similar pattern in developing resistance to many types of insecticides used to control crop pests. Insecticide resistance is a global issue for a wide variety of agriculturally important pests and has been reported in over 540 insect and mite species (www.pesticideresistance.com).

Nebraska has had a long history with insecticide-resistant pests. The western corn rootworm has been particularly difficult and has developed resistance to numerous insecticides for both larval and adult controls. In addition, corn rootworm in parts of Nebraska and the Midwest have developed resistance to some of the Bt proteins found in genetically modified corn, leaving growers with fewer control options and greater management costs. In the United States alone, crop losses due to pesticide resistance are estimated at $1.4 billion annually.

Stevan Knezevic
Extension Weeds Specialist

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