Previous studies showed that sub-micromolar concentrations of the microtubule-targeting herbicide propyzamide cause a right-handed helical arrangement of cortical microtubule arrays and left-handed twisting in elongating Arabidopsis epidermal cells. When seedlings were grown in the presence of 1-2 microM propyzamide or 50-100 nM oryzalin, we show that microtubules spent more time in a paused state in which they exhibited little net change in length. The drug treatment also resulted in slower growth and shortening velocities, increased catastrophe, and an overall decrease in microtubule turnover. A reduction in microtubule dynamic turnover may underlie the drug-induced rearrangement of cortical arrays.