The effects of soil solarization and soil fumigation on Fusarium wilt of watermelon grown in plastic house in south‐eastern Spain

The effects of pre‐planting solarization or fumigation with metham‐sodium of sand‐mulched soil on fusarium wilt of watermelon in plastic house culture were investigated at Almeria, south‐eastern Spain. In two trials, 2 months' solarization increased the average maximum soil temperature by c. 5°C to 44‐48° C at 10 cm depth and by 4‐5° C to 40‐42° C at 20‐30 cm. The amount of Fusarium oxysporum in the upper 15 cm of a naturally infested soil was reduced by solarization and by fumigation. During the 9 months following treatment, the F. oxysporum population stabilized at a low level in soil solarized for 2 months, but fluctuated in soil solarized for 1 month and increased in fumigated soil. The amount of wilt in watermelon sown into this soil after treatment was generally low; plants growing in solarized or fumigated soil suffered less wilt than plants in untreated soil but the differences were not significant. In a soil artificially infested with the highly pathogenic race 2 of F. oxysporum f. sp. niveum, F. oxysporum populations were greatly reduced following solarization or fumigation, and fluctuated erratically thereafter. Solarization for 2 months completely controlled wilt in watermelon and gave a fruit yield almost five times that of plants in untreated soil. Solarization for 1 month only slowed disease development slightly but gave a yield more than twice that in untreated soil. Fumigation with metham‐sodium retarded disease development considerably and tripled fruit yield. Plant performance was significantly better in soil solarized for 2 months than in uninfested control soil, suggesting beneficial effects of this treatment additional to wilt control.