Solar Heating in Closed Plastic House for Control of Soilborne Diseases

V. Application for Control of Fusarium Wilt of Strawberry

Abstract

Soil disinfestation by solar heating in closed plastic house was examined for applicability in control of Fusarium wilt of strawberry. During midsummer, experimental plastic house was entirely sealed and the soil surface was mulched with plastic film. To keep the soil in high moisture level, the soil was temporarily irrigated with sufficient volume of water before mulching. When soluble starch (25, 50g/kg dry soil) was ploughed into naturally infested soil before being submerged, solar heating treatment was more effective. The lethal exposure limit to the causal fungus was assumed to be 8-14 days at 40C. Soil temperature at 20cm deep in closed plastic house reached to 40C, effective lethal temperature, within 3 days in more insolated summer, but within 5 days in less insolated summer. To keep the temperature at 40C throughout day and night, 12-17 days were necessary in more insolated summer, but 20 or more days were necessary in less insolated summer. It was considered that rapid increase of soil temperature at 20cm deep in closed plastic house varied coincidentally with air temperature in the open field, especially with averaged maximum atmospheric temperature for 3 consecutive days. The following equation was obtained: Y=2, 37X-33.27, r=0.889^**, where Y=soil temperature (C) at the depth of 20cm in the plastic house; X=averaged maximum atmospheric temperature of 3 consecutive days in the open field. However, it might be necessary to adjust this epuation according to size of the house or some other factors affecting the temperature in the tested plastic house. In naturally infested strawberry field, the temporarily submerged soil was mulched with plastic film in closed plastic house during July and August in several years. Population density of Fusarium oxysporum in the soil at 10-20cm deep decreased rapidly, and even 9 months after the treatment only a few of the fungus was recovered. Field experiments which were carried out in naturally infested strawberry field for 2 years demonstrated that solar heating treatment should be applicable to control Fusarium wilt of strawberry, and it brought an increase in yield and growth of the plant.