Weed management practices determine plant and arthropod diversity and seed predation in vineyards

In the Central Coast of California, USA, wine grape growers are making efforts to identify weed control practices that preserve biodiversity in their vineyards while maintaining yields. A field study was conducted in Paso Robles, California in 2006 and 2007 evaluating the effect on plant and ground dwelling arthropod communities of five weed control practices conducted under the vines within the row (berm): (i) flumioxazin, (ii) simazine, (iii) cultivation, (iv) cover crop and (v) untreated control. The cover crop, cultivation and untreated control had 4-50 times higher plant density and more than 15 times higher plant diversity compared with the herbicide treatments. The arthropod activity-density differed among treatments only in 2007, being higher in the cover crop and untreated control. There was a positive relationship between plant and arthropod diversity (r(2) = 0.42, P = 0.02 in 2006; r(2) = 0.64, P < 0.001 in 2007). Laboratory seed predation tests of the two most frequently captured carabid beetles, Calathus ruficollis and Tanystoma maculicolle, indicated they predated more of the common weed species Brassica nigra and Capsella bursapastoris, than other weed species tested. Under field conditions, treatments with higher plant diversity and density favoured arthropod seed predation of these weeds. Predation rates were 20-40% in the cover crop and untreated control, double that observed in the herbicide treatments. The cultivation treatment balanced the benefits of promoting diversity while minimising yield reductions caused by weed competition. The results indicate that weed management practices that promote higher plant diversity and density have the potential to yield ecological benefits within vineyards, for example, enhancing the activity of beneficial organisms.