Weed control in container nursery plants is a major production problem, especially for perennial plants grown in field nurseries over time (Altland, 2003). Weeds compete with the nursery plants for available resources, harbor pests and diseases, and downgrade crop quality. Although preventive weed control measures, including exclusion, groundcovers, and cultivation, are used in adjacent land, chemical weed control, especially with granular preemergent herbicides, is widely used in production areas (Norcini and Stamps, 1994).
Preemergent herbicides such as isoxaben (Gallery DF; Dow Agrosciences, Indianapolis, IN), napropamide (Devrinol; United Phosphorus, Trenton, NJ), prodiamine (Barricade; Syngenta, Wilmington, DE), s-metolachlor (Pennant; Syngenta), and oxyfluorfen (Goal; Dow Agrosciences) are commonly used for weed control in containerized nurseries. However, nonchemical control methods have also been actively researched and used. Chong (2003) used discs made of semirigid plastic, fabrics, polyfoam, pressed peatmoss, and insulated blankets that provided both winter freeze protection and weed control. Organic mulches like chipped and shredded tree bark, pelletized shredded newspaper, and rice hulls have reduced weed growth in container nurseries (Mathers and Ozkan, 2001), but can also reduce nitrogen availability because of high carbon:nitrogen ratios (Billeaud and Zajicek, 1989). Herbicide-treated Douglas Fir (Pseudotsuga menziesii) bark nuggets provided a 150% increase in weed control efficacy over preemergent herbicides and reduced nursery plant phytotoxicity (Mathers, 2003).
Research on the use of natural products for weed management has focused primarily on agronomic and horticultural field crops with little application to containerized plant production (Weston, 2005). However, wood chips and leaf mulches from several woody perennials, including southern redcedar and southern magnolia, may contain water-soluble natural products with phytotoxic activities and they could therefore be used for suppressing weeds in horticultural production systems (Rathinasabapathi et al., 2005). The objective of this study was to evaluate the suitability of weed-suppressive wood chip mulches for weed control in nursery container plants.
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