Weed control and yield response of soil solarization with different plastic films in lettuce.

Phase out of most chemicals available for weed management renewed the interest in soil solarization as a technically effective and environmentally safe practice for lettuce weed control in hot summer areas. Properties of solarizing films and lettuce crop system may considerably affect weed control and yield response of soil solarization. Different solarizing films, including low-density polyethylene, ethylene-vinyl acetate copolymer, low-density polyethylene–ethylene-vinyl acetate coextruded and a biodegradable corn starch-based film, were evaluated in 2003 and 2004 for weed control and lettuce yield response under field and greenhouse conditions in Southern Italy. Soil solarization strongly reduced weed density and biomass in both greenhouse and in the field, with no significant differences among the tested plastic films. Most annual weeds were completely controlled by soil solarization, except amaranth, Amaranthus spp., in soil solarized with biodegradable film in the field. Emergence of mediterranean sweetclover, Melilotus sulcatus, was stimulated by soil solarization in greenhouse. In the field, Cyprus vetch, Lathyrus ochrus, was found in solarized plots though absent in untreated soil. Perennial weeds were not affected by soil solarization, except a strong control of canadian thistle, Cirsium arvense, in the field. Lettuce yield resulted significantly higher in solarized soil than in control plots, with no significant differences among the solarizing materials. All tested materials proved to be technically effective for soil solarization in lettuce, though low resistance and short durability of biodegradable film may suggest its application mainly to soil solarization in greenhouse or in organic systems.