Abstract: Diagnosing herbicide-resistant weeds as a first step in resistance management and monitoring their nature, distribution, and abundance demands efficient and effective screening tests. This review summarizes and recommends appropriate seed sampling techniques, protocols for screening weeds for resistance to herbicides of different sites of action, interpretation of results, and information given to the grower. Elements common to all screening procedures are reviewed. Choosing appropriate discriminating doses to distinguish between resistant and susceptible weed biotypes is the most important factor in achieving accurate and consistent results. Interpretation of results is also critical because resistant weeds may comprise a small portion of the population in suspected accessions or biotypes.

Additional index words: Bioassay, discriminating dose, seed sampling, site of action, surveys.

Abbreviations: ACCase, acetyl-CoA carboxylase (EC 6.4.1.2); ALS, acetolactate synthase (EC 4.1.3.18); AOPP, aryloxyphenoxy propionate; CHD, cyclohexanedione; DAT, days after treatment; EPSP synthase, 5-enolpyruvylshikimate-3-phosphate synthase (EC 2.5.1.19); KARI, ketol-acid reductoisomerase (EC 1.1.1.86); POST, postemergence; PRE, preemergence; R, resistant; S, susceptible.