Solarization for Weed Control

Solarization is a method of heating moist soil by covering it with plastic sheets to trap solar radiation. In field experiments in Israel during the summer, maximum soil temperature under plastic cover at the 5-cm depth averaged 46 to 49C. No weeds emerged under the plastic cover during solarization and weed emergence was reduced after its removal. The heating effect from solarization decreased with soil depth. Concentration of O 2 in soil under plastic was similar to that in uncovered controls, but the concentration of CO 2 was markedly higher than in control soil, rising up to 2.4%. Higher temperatures and better residual weed control were produced by transparent than by black plastic, with best results from thin (0.03 mm), transparent polyethylene. Under Israeli summer conditions, 2 to 4 weeks of solarization produced effective control of annual weeds that was still appreciable after 1 yr. Narrow sheets of 20 to 50 cm produced effective weed control in bands. on soil irrigated once before placing the plastic sheets, there was no need to irrigate during solarization. The response of weed species to solarization differed. Many annual weeds, both summer species such as pigweed ( Amaranthus spp.) and common purslane ( Portulaca oleracea L.) and winter species as henbit ( Lamium amplexicaule L.) were well controlled by solarization. Broomrape ( Orobanche crenata Forsk.) was controlled in one experiment. on the other hand, horseweed Conyza canadensis (L.) Cronq. and bull mallow ( Malva niceaensis All.) were relatively resistant, and established perennials escaped the treatment.