Greenhouse soil solarization: effect on weeds, nematodes and yield of tomato and melon

Phase-out of methyl bromide and health concerns related to the use of pesticides are increasing the interest in alternative control strategies. Soil solarization is an effective, safe and cheap technique for the control of soil-borne pathogens and weeds. However, knowledge of the long-term effects of solarization, as well as of repeated solarization cycles, is scarce. Such knowledge should in particular help to minimize the number of solarization treatments. Therefore, we tested the residual effect of a single solarization treatment and the effects of two or three solarization cycles on root-knot nematodes, weeds and crop yield for three years on greenhouse-grown tomato and melon. Soil solarization was applied for either one, two or three consecutive years on a soil infested by the root-knot nematode Meloidogyne javanica and many annual and perennial weed species. An untreated soil was used as a control. At the end of each crop cycle yield parameters were recorded, weeds were identified and counted, and nematode infestation was evaluated. Our results show that a single solarization treatment significantly increased yields by +116%, and strongly reduced nematode infestation of -99% of infested plants and of -98% of the root gall index in the following melon crop. It also suppressed annual weed emergence three years later. Plant yields from two- and three-year solarized soil were always higher than nonsolarized control: +284% and +263%, respectively, for tomato, and +162% and +368%, respectively, for melon. Further, two- and three-year solarization treatments almost completely suppressed the infestation of the M. javanica nematode in tomato, and reduced the nematode effect in melon by -86% and -79%, respectively. Repeated solarization treatments also resulted in a high reduction of emergence of most weed species in all crop cycles. A single soil solarization treatment was shown to be effective for a long-term sustainable management of weeds, whereas the time-limited effectiveness against root-knot nematodes can be enhanced through two- or three-year repeated treatments.