Herbicide Failure, Weed Resistance, and Pesticide “Stewardship”

Success or failure? There are a number of important factors that affect the outcome of weed control.

If you are a pesticide applicator, you may have encountered some herbicide treatments that did not produce the results you expected.  Why is that?  There are a number of factors that can contribute to less than perfect pesticide treatment results.  With proper pesticide knowledge and stewardship, however, most of these factors can be avoided.

Pesticide failure can occur for a variety of reasons:

  • Improper pest/weed identification
  • Selection of an incorrect pesticide
  • Unfavorable environmental conditions (drought, storms, wind)
  • Poor condition/degradation of the pesticide product due to improper storage, heat, humidity, or cross contamination
  • Development of pesticide resistance
  • Incorrect application due to:
    • application at the wrong time of year,
    • application at the wrong growth stage of target pest
    • failure to follow label application instructions – pesticide never reaches the target pest
    • poorly calibrated equipment resulting in incorrect application rate or dose
    • incorrect, or no adjuvants

Herbicide Resistant Weeds

There is a lot of news, lately, regarding herbicide resistant agricultural weeds.  Resistance of agricultural weeds is not a new phenomenon, in fact, the first recorded herbicide-resistant weed, 2,4-D resistant spreading dayflower (Commelina diffusa), was identified in 1957 in a sugarcane field in Hawaii. (B. A. Sellers, et. al., 2005).  While it may not be a new phenomenon, the number of resistant weeds has increased dramatically in the last 30 years (http://weedscience.org/in.asp).  Worldwide, there are over 390 resistant plant biotypes. Why the increase?  It’s a numbers game.  Herbicides don’t actually cause the resistance, but that one-in-a-million plant which is capable of resisting the herbicide survives to spread its seeds.  Every seed is another opportunity for that 1-in-a-million mutation, and repeated use of the same herbicide, or mode-of-action can ultimately select for a herbicide resistant plant.

Herbicide Stewardship and IPM

Pesticides are but one of the valuable tools available to pest managers and they should be used as part of an overall integrated pest management (IPM) plan.  The take home message for weed managers everywhere now, is herbicide Stewardship.  Responsible stewardship of pesticides is critical for maintaining their effectiveness, and keeping them in your toolbox!  The key to successful weed management is responsible stewardship using integrated pest management techniques such as:

  • Chemical control (incorporating different herbicides with different modes of action)
  • Mechanical control
  • Hand removal
  • Management of escaped weeds
  • Clean, decontaminated, well calibrated equipment
  • Crop rotation
  • Tillage (of all types)
  • Cover crops
  • Continued education and field knowledge
  • Well-kept pesticide treatment records and observations.

If you do experience a less than ideal pesticide treatment, keep in mind the above factors that can affect your application.  Review your records.  Don’t explain away a herbicide failure; do your best to figure out why it happened so it is not repeated.  If resistance is suspected, contact your local agriculture extension agent, and manage it early!  For more information on these topics please see the following UF/IFAS publications online:

When a Pesticide Doesn’t Work

Herbicide Resistant Weeds

UF/IFAS Pesticide Information Office

Amaranthus palmeri “Palmer amaranth”

Leave a Reply

Your email address will not be published. Required fields are marked *