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Long-Term Effects on Vegetation of Herbicide Treatments in Chaparral

  • Jodie S. Holt (a1), Steven R. Radosevich (a2) and Walter L. Graves (a3)


Field studies were established in 1974 and 1975 at various locations in San Diego County, CA, to evaluate several herbicides for the control of chamise (Adenostoma fasciculatum H.&A.) and redshank chamise (Adenostoma sparsifolium Torr.). Herbicide effects on vegetation were reevaluated in 1982. Plots originally treated with 2.2 or 4.5 kg ae/ha of glyphosate [N-(phosphonomethyl)glycine] had virtually no chamise regrowth 8 yr after treatment. The herbicides 2,4-D [(2,4-dichlorophenoxy)acetic acid], combinations of 2,4-D with 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] or dichlorprop [2-(2,4-dichlorophenoxy) propionic acid], fosamine [ethyl hydrogen (aminocarbonyl)phosphonate], triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, and picloram (4-amino-3,5,6-trichloropicolinic acid) had no long-term effects on chamise. Soil collected in 1982 from glyphosate-treated plots contained similar numbers of chamise seeds but fewer seeds of other species compared to untreated plots. Canopy cover of redshank chamise was similar in treated and untreated plots after 8 yr. These results document the effectiveness of glyphosate in killing the underground root-crown of chamise, which prevented sprouting, but not redshank chamise.



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