A weed species that has developed resistance to herbicides in Kansas includes:

• A. Kochia
• B. Cheat
• C. Palmar Amaranth
• D. All of the above

Answer: (D)

Herbicide resistance happens when a weed population is exposed repeatedly to the same herbicide and the individuals with heritable tolerance survive and reproduce, gradually making the population harder to kill with that mode of action. In Kansas, evidence shows that kochia, Palmer amaranth, and cheat have all developed resistance to herbicides. Kochia has shown resistance to glyphosate in this region, Palmer amaranth is one of the most notorious resistant species, and cheat has also been documented to survive certain herbicide applications. Because each of these weeds has resistant populations in Kansas, the best answer is that all of the above are resistant. This underlines the need for diverse, integrated weed management—rotating modes of action, using tank mixes or residuals, and employing cultural practices to reduce reliance on a single herbicide.