Yellow Nutsedge Management in Strawberry.

Yellow nutsedge (Cyperus esculentus) is one of the most problematic weeds in organic strawberries. Hand weeding nutsedge is only partially effective and can exceed $ 9, 000/ha in labor costs.  In 2008-2009 at Camarillo, California we evaluated physical barriers for control of yellow nutsedge in raised beds covered with black polyethylene (PE) mulch alone (untreated control) or with: 1) paper (recycled newspapers, gypsum) laid under PE mulch or 2) paper in-between two PE mulch layers; 3) water-resistant Tyvek Home Wrap (DuPont) or 4) Weed Barrier mat under PE mulch and 5) Duraskrim (0.167 mm thick line PE plastic) applied alone. Additionally, we tested bed-applied steam (via four surface hoses with 15 cm spike injectors) to raise soil temperatures to about 70°C for 20 minutes. We obtained near 100% control throughout the nine months of the strawberry season with paper placed between 2 PE layers, Tyvek, Weed Barrier mat or Duraskrim and 80-90% control after steam application. Due to warm soil temperatures in 2008-2009 nutsedge shoots continued to emerge throughout the season in untreated controls at 0.5 to 2.8 plants/m² per week in fall and 4 to 5 plants/m² in spring.  Approximate expenses for hand-weeding at these weed densities ranged $12, 350 to $14,820 /ha and weeding required labor diversion from fruit harvest.  Approximate costs of barriers were: $ 2,900/ha (paper between 2 plastic layers), $10,620/ha (Weed Barrier), $11,850 (Tyvek) and 16, 000/ha (Duraskrim). Duraskrim and Weed Barrier restricted plant placement and expansion, resulting in smaller, less productive plants compared to other treatments, while plants in steam treatment were largest and most productive. These studies showed that investment in physical control tools may be justified in areas with high nutsedge density. Steam may provide complete soil disinfection but efficient and economical application methods need to be further developed.