Most weed control failures are not due to resistance. Before assuming weeds surviving an herbicide application are resistant, eliminate other possible causes of poor control:

1. Herbicide application

a. Inadequate rate

b. Poor spray coverage and/or incorporation

c. Improper timing of application of postemergence herbicides (after weeds are too large to control)

d. Failure to use an adjuvant (if needed)

e. Excessive dust with post-emergence applications

f. Spray intercepted at application by wheel traffic

g. Antagonism between two or more herbicides

2. Soil and/or climatic conditions

a. Excessively wet or dry soil

b. Seedbed condition (clods, etc.)

c. Herbicide adsorption to soil particles or organic matter
d. Stress conditions, such as hot and dry

e. Lack of timely rainfall for activation

f. Wash-off of postemergence herbicides

Herbicide Resistance Terms to Know Understand the difference between population shift and resistance, as well as other concepts.

Is Herbicide Resistance to Blame?
Resistance is not the only cause of weed control failure

Incidence and History of Herbicide Resistance
Resistance to one or more of 25 herbicide families has been observed in the U.S.

Mechanisms of Herbicide Resistance
How does resistance develop in a population?

Proactive Herbicide Resistance Management
Methods to help slow or prevent the development of herbicide resistance.

How to Manage Herbicide Resistance.
What you can do if resistance is already a problem

Herbicide Spraying by the Numbers
Use information on pesticide labels to rotate herbicide "families"

Resources and Suggested Reading Additional information about herbicide resistance.

Resistance Lessons
Resistance lessons provided courtesy of the Weed Science Society of America

Introduction to Pesticide Resistance

PES Home

Additional Resources
Weedscience.org