2019 ASHS Annual Conference

Soil solarization places thin (1-2mil), clear plastic over soil to generate lethal temperatures for weed seeds and soilborne organisms. Finding thermal death thresholds for important weed seeds in California agriculture can help growers more effectively use soil solarization in their fields. Lab experiments simulating soil solarization conditions tested weed seeds at five soil temperatures that occur during solarization in California (40°C, 45°C, 50°C, 55°C, and 60°C). Seeds tested included little mallow, redstem filaree, bristly oxtongue, annual sow thistle, common purslane, common lambsquarters, and redroot pigweed. Efficacy of solarization temperatures differed between different species. Cool season annuals annual sow thistle and bristly oxtongue were more susceptible to heat treatments than warm-season annuals redroot pigweed and common lambquarters. Common purslane and hard seeded weed species little mallow and redstem filaree were the least susceptible to heat treatments. Complete (100%) mortality was achieved at all temperatures tested for lambsquarters, sow thistle, and bristly oxtongue. Redroot pigweed was not affected by 40°C treatments. Common purslane, redstem filaree, and little mallow were not affected by 45°C and 40°C treatments. All seeds were tested at 3 or more different times at temperatures where heat treatments increased weed seed mortality. Time and percent mortality of weed seeds were used to create thermal death models for weed seeds.