Appearance of Herbicide Resistance in a Weed Population

Through the repeated imposition of the same herbicide, susceptible (S)‐biotypes of a weed species are controlled and herbicide resistant (R)‐biotypes of the same weed species are left behind to reproduce and return seed with the resistance characteristic back into the soil. This lesson will highlight the population dynamics of a mixed weed population (S‐ and R‐biotypes) and compare and contrast the rate at which herbicide resistance appears in a weed population under a diversity of selection pressures. At the completion of this lesson, students will: Understand the differences between susceptible, tolerant, and resistant weed populations. Describe diagrammatically and mathematically, the dynamics of an annual weed species population composed of Sand R‐biotypes. Describe herbicide characteristics, aspects of weed species biology, and management practices that alter intensity of selection pressure and impact the rate at which herbicide resistance appears in a weed population. Devise a weed management plan with a diversity of selection pressures to reduce the rate at which herbicide resistance appears. A bank of quiz questions targeting these objectives is a part of the lesson. The lesson is designed to meet the education needs of graduate students and advanced extension audiences.