|Welker, William - RET. PLANT PHYSIOLOGIST|
Submitted to: Weed Technology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 26, 1999
Publication Date: N/A
Interpretive Summary: Herbicides such as diuron, simazine, and terbacil have been available for nearly thirty years and have been applied repeatedly for weed control in fruit orchards. There is concern that with frequent use, weed populations that are resistant to such herbicides may become dominant. In this study, these herbicides were applied alone or in combination continuously for fifteen years under typical grower field conditions. Over 15 years, terbacil was much more effective in controlling weeds than simazine or diuron. Results indicate that herbicide resistant weed populations did not occur, probably because the herbicides were applied only to restricted space in strips below trees. In addition, weed diversity did not change much over the fifteen years of the study, suggesting that repeated use of diuron, simazine, and terbacil will contribute to a stable, manageable weed community.
Technical Abstract: Diuron, simazine, and terbacil were applied together or separately in the field each May from 1981 through 1996. Weed control was excellent in 1981 and 1982 but by 1984 weed abundance increased in plots treated with diuron and simazine. Weed abundance was relatively low from 1981 through 1996 in plots treated with terbacil. Broadleaf and grass species abundance was similar in most herbicide-treated plots. Perennial species, particularly fescue and ailanthus, dominated sites treated with diuron and simazine. The weed community changed within three years of the implementation of the weed management program that relied solely on herbicides. A relatively stable weed community persisted from 1992 through 1996. Repeated use of diuron, simazine, and trebacil did not result in proliferation of herbicide-resistant weeds, indicating that these herbicides are appropriate for long-term weed management programs in orchards.