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Integrating 2,4-D and Sheep Grazing to Rehabilitate Spotted Knapweed Infestations

Roger L. Sheley, James S. Jacobs and John M. Martin
Journal of Range Management
Vol. 57, No. 4 (Jul., 2004), pp. 371-375
DOI: 10.2307/4003861
Stable URL: http://www.jstor.org/stable/4003861
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Integrating 2,4-D and Sheep Grazing to Rehabilitate Spotted Knapweed Infestations
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Abstract

Effective integrated weed management requires understanding the impacts of management strategies applied alone and in combination. The objectives of this study were to determine the effects of 2,4-D and repeated sheep (Ovis aries) grazing applied alone and in combination on spotted knapweed (Centaurea maculosa Lam.) and perennial grasses. We hypothesized that integrating a single spring 2,4-D application would remove the adult plants, repeated sheep grazing would control rosettes, and spotted knapweed density, cover and biomass would decrease, allowing residual grasses to reoccupy the sites. A single spring 2,4-D application at $2.1\ {\rm kg}\ {\rm a}.{\rm i}.\ {\rm ha}^{-1}$, repeated annual sheep grazing of 95% spotted knapweed or 60% grass utilization, and repeated sheep grazing and 2,4-D combined were applied to small pastures at 2 sites in western Montana beginning in 1997 and continued through 2001. Spotted knapweed rosette and flowering plant density, and spotted knapweed and perennial grass cover and biomass were sampled from 1998 through 2001. Spotted knapweed rosette density was 61.7, 34.3, 44.3, and $0.3\ {\rm m}^{-2}$ in the control, sheep grazing, 2,4-D, and combined sheep grazing and 2,4-D treatments, respectively, at 1 site in 2001. Spotted knapweed flowering plant density increased from 3.7 in 1998 to $10.7\ {\rm m}^{-2}$ in 2002 in the 2,4-D treatment whereas there was no increase in the 2,4-D combined with sheep grazing treatment from 1998 to 2002. Perennial grass biomass was 6.9, 8.4, 25.7, and 19.7 in the control, sheep grazing, 2,4-D, and combined sheep grazing and 2,4-D treatments, respectively, averaged for both sites and 4 years of sampling. Herbicides released perennial grasses from weed competition and changed the weed population from mature, less palatable plants to juvenile plants that were preferred by sheep. /// Un manejo integrado de maleza efectivo requiere del entendimiento de los impactos de las estrategias de manejo aplicadas solas o en combinación. Los objetivos de este estudio fueron determinar los efectos de 2,4-D y el apacentamiento repetido de ovinos (Ovis aries), aplicados solos y en combinación, sobre el "Spotted knapweed" (Centaurea maculosa Lam.) y los zacates perennes Hipotetizamos que integrando una sola aplicación de 2,4-D en primavera removería las plantas adultas y el apacentamiento repetido con ovinos controlaría las rosetas y por lo tanto la densidad, cobertura y biomasa de "Spotted knapweed" decrecerían permitiendo a los zacates perennes remanentes ocupar nuevamente los sitios. En potreros pequeños de dos sitios del oeste de Montana se aplicaron los siguientes tratamientos: una sola aplicación en primavera de 2,4-D a razón de $2.1\ {\rm kg}\ {\rm i}.{\rm a}.\ {\rm ha}^{-1}$, apacentamiento anual repetido por ovinos del 95% del "Spotted knapweed" o el 60% de utilización de los zacates y el apacentamiento repetido mas aplicación de 2,4-D, el estudio inicio en 1997 y continuo hasta el 2001. La densidad de rosetas y plantas floreando de "Spotted knapweed" y la biomasa y cobertura de "Spotted knapweed"y zacates perennes se muestrearon de 1998 al 2001. En el sitio 1, en el 2001 la densidad de rosetas de "Spotted knapweed" fue de 61.7, 34.3, 44.3 y $0.3\ {\rm m}^{-2}$ en los tratamientos control, apacentamiento de ovinos, 2,4-D y la combinación de ambos respectivamente En el tratamiento de 2,4-D la densidad de plantas floreando de "Spotted knapweed" se incrementó de 3.7 en 1998 a $10.7\ {\rm m}^{-2}$ en el 2002 mientras que en el tratamiento de la combinación de 2,4-D con apacentamiento con ovinos no se registro incremento alguno. La biomasa de zacates perennes, promedio de los dos sitios y los cuatro años de muestreo, fue de 6.9, 8.4, 25.7 y 19.7 en el tratamiento control, apacentamiento con ovinos, 2,4-D y la combinación de 2,4-D con apacentamiento con ovinos respectivamente. Los herbicidas liberaron a los zacates perennes de la competencia ejercida por la maleza y cambiaron la población de maleza de una madura y menos gustosa a plantas juveniles que fueron preferidas por los ovinos.

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