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Imazapic Activity in a Semiarid Climate in Downy Brome (Bromus tectorum)–Infested Rangeland and CRP Sites

  • Krista A. Ehlert (a1), Richard E. Engel (a1) and Jane M. Mangold (a1)


Chemical control of downy brome has focused on imazapic; however, imazapic efficacy in semiarid climates is unpredictable, possibly because of variable residual soil activity. Our objective was to characterize imazapic activity over 9 mo in rangeland and a Conservation Reserve Program (CRP) site following its application in the fall as affected by rate (0, 80, 160, 240 g ai ha−1) and quantity of plant residue (reduced, ambient). Greenhouse bioassays were conducted over two seasons (2010 to 2011 and 2011 to 2012) using soil collected at multiple dates after imazapic application. Quantity of plant residue did not affect downy brome biomass or response to imazapic. Imazapic reduced downy brome biomass (P < 0.05) across all sampling dates in both seasons, and the response to rates was consistent up to 200 d post application. Imazapic activity over time conformed to a biphasic model with activity being consistent, or slightly improving, up to about 160 and 150 d post application, and then dropping rapidly to the final sampling event 287 and 272 d post application in rangeland and at CRP sites, respectively. These results indicate that fall imazapic applications in semiarid climates persist into the spring, thus providing control of both fall-emerging downy brome seedlings and seeds that overwinter and emerge the following spring.

El control químico de Bromus tectorum se ha enfocado en imazapic. Sin embargo, la eficacia de imazapic en climas semiáridos es impredecible, posiblemente por su variable actividad residual en el suelo. Nuestro objetivo fue caracterizar la actividad de imazapic a lo largo de 9 meses después de su aplicación en el otoño, la influencia de sitios bajo el Programa de Reservas para Conservación (CRP), el efecto de la dosis (0, 80, 160, 240 g ai ha−1) y la cantidad de residuos vegetales (ambiental, reducida). Se realizaron bioensayos de invernadero durante dos temporadas (2010 a 2011 y 2011 a 2012) usando suelo colectado en múltiples fechas después de la aplicación de imazapic. La cantidad de residuo vegetal no afectó la biomasa de B. tectorum o la respuesta a imazapic. Imazapic redujo la biomasa de B. tectorum (P < 0.05) en todas las fechas de muestreo en ambas temporadas, y la respuesta a las dosis fue consistente hasta 200 d después de la aplicación. La actividad de imazapic a lo largo del tiempo se ajustó a un modelo bifásico teniendo una actividad consistente o ligeramente mejorando, hasta cerca de 160 y 150 d después de la aplicación, y luego cayendo rápidamente en el evento final de muestreo a 287 y 272 d después de la aplicación en pastizales y en sitios CRP, respectivamente. Estos resultados indican que las aplicaciones de imazapic en el otoño en climas semiáridos persisten hasta la primavera, bridando así control de plántulas que emergen en el otoño de B. tectorum y semillas que sobreviven el invierno y emergen durante la siguiente primavera.


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Imazapic Activity in a Semiarid Climate in Downy Brome (Bromus tectorum)–Infested Rangeland and CRP Sites

  • Krista A. Ehlert (a1), Richard E. Engel (a1) and Jane M. Mangold (a1)


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