Herbicide Resistance in Jointed Goatgrass (Aegilops cylindrica): Simulated Responses to Agronomic Practices1

Abstract

A population model was constructed to simulate the development of imazamox-resistant jointed goatgrass (AEGCY) in imazamox-resistant (Clearfield™) wheat. The model computed changes in the surface and in the buried AEGCY seed banks for both resistant and susceptible biotypes. Simulations started with an initial density of 1,000 susceptible and zero resistant seeds/m2 in each seed bank. Simulation of continuous, no-till Clearfield wheat production resulted in rapid development of resistant AEGCY without hybridization with wheat and in extremely rapid resistance development with hybridization. In less than 10 yr, the resistant population was growing exponentially in both simulations. Adding a fallow year with tillage into the simulated rotation did not substantially slow down the appearance of resistance but did delay the rate of resistant population increase by several orders of magnitude over 10 yr. Alternating Clearfield and a nonresistant winter wheat in combination with fallowing prevented the establishment of a significant resistant AEGCY population and prevented the susceptible seed population from increasing exponentially. These projections suggest that imazamox-resistant wheat can be a tool for managing AEGCY populations especially if combined with rotations that include fallow and crops other than Clearfield winter wheat.Nomenclature: Imazamox; jointed goatgrass, Aegilops cylindrica Host #3 AEGCY; winter wheat, Triticum aestivum L. Clearfield™.Additional index words: Crop rotation, pollen flow, population model, resistance management.Abbreviations: ALS, acetolactate synthase; BSB, buried seed bank; DSP, local seed dispersal; EST, established plant; MAT, mature plant; PRD, seed production; SDL, seedling; SSB, surface seed bank.