ARS | Publication request: Alternatives to Preemergence Herbicides in North Coast Vineyards

Submitted to: Weed Science Society Of California Meeting Proceedings
Publication Acceptance Date: February 13, 2004
Publication Date: July 30, 2004
Citation: Baumgartner, K. 2004. Alternatives To Pre-Emergence Herbicides In North Coast Vineyards. 56th Annual Conference Of The California Weed Science Society. Major Presentation.

Interpretive Summary: California winegrape growers are under increasing pressure to decrease use of preemergence herbicides in order to achieve water quality standards established by public regulatory agencies. Alternative weed control practices are available, but their efficacy is not known. Our objective is to examine the efficacy of alternative weed control practices. Our berm study addresses the use of alternatives to preemergence herbicides (Roundup®, in-row soil cultivation, Matran'; used alone and in combination) used on berms, where weeds are directly controlled. Our middles study addresses the effects of cover crops (annual till, annual no-till, perennial no-till) planted in vineyard middles on weed population dynamics on adjacent berms. We initiated both experiments in 11/2002 in a commercial, drip-irrigated winegrape vineyard in Napa Co., CA. The most effective berm treatment was Winter Roundup®/Spring Roundup®. The least effective were Winter Matran'/Spring Matran' and Spring cultivation. Intermediate were treatments with a Fall cultivation. Matran' was very effective against broadleaves, but least effective against grasses. However, given that Matran' controlled the more problematic broadleaves, it was successful. Winter Roundup®/Spring Roundup® had the lowest weed biomass, but also the lowest weed diversity, suggesting that the two weeds present in this treatment may be increasingly difficult to control with Roundup®. The most vigorous cover crops, the annuals, were better at competing with weeds in the middles. Therefor, there were fewer weeds in berms adjacent to annual cover crops. Over time, the perennial no-till cover crop will likely develop a denser canopy, enabling it to compete better.

Technical Abstract: The objectives of our research are to test the efficacy of alternative weed control strategies on not only weed establishment, but also on grapevine yield, growth, and nutrition. Our berm study addresses the use of alternatives to preemergence herbicides (Roundup®, in-row soil cultivation, Matran'; used alone and in combination) used on the berms, where weeds are directly controlled. Our middles study addresses the effects of cover crops (annual till, annual no-till, perennial no-till) planted in vineyard middles on weed population dynamics on adjacent berms. We initiated both experiments in 11/2002 in a commercial, drip-irrigated winegrape vineyard in Napa Co., CA. The most effective berm treatment, based on total weed biomass, was Winter Roundup®/Spring Roundup®. The least effective were Winter Matran'/Spring Matran' and Spring cultivation. Intermediate were treatments with a Fall cultivation. Matran' was very effective against broadleaves, but least effective against grasses. However, given that Matran' controlled the more problematic broadleaves, it was successful. Winter Roundup®/Spring Roundup® had the lowest weed biomass, but also the lowest weed diversity, suggesting that the two weeds present in this treatment, Vulpia myuros var. hirsuta and Epilobium brachycarpum, may be increasingly difficult to control with Roundup®. Weed biomass in the middles and adjacent berms was significantly lower in both annual cover crop treatments than in the perennial cover crop treatment. Among the three cover crops, the vigorous annuals had the highest cover crop biomass and the lowest weed biomass. Their ability to compete with weeds in the middles was associated with lower weed biomass in adjacent berms. Over time, the perennial, no-till cover crop will likely develop a denser canopy enabling it to compete better with weeds in the middles.