Loss of Viability of Dematophora necatrix in Solarized Soils

To study the relationship between temperature regimes and loss of viability of Dematophora necatrix in soil, two field experiments were conducted to determine the effectiveness of soil solarization on reducing the population of D. necatrix colonizing avocado root segments buried at a depth of 15–60cm. Increase of maximum hourly temperatures attributable to soil solarization reached, depending on depth, 6.7–4.6°C in unshaded areas and 3.9–1.5°C for shaded areas in the first experiment (starting in early June, 1995). The better environmental conditions in the second experiment (starting by mid-July, 1995) led to higher temperature increases (8.6–5.6°C, depending on depth) when solarization was conducted in unshaded areas. One, 4, 5 and 6 weeks of solarization were required to eliminate the viability of D. necatrix at 15, 30, 45 and 60cm depths in the first experiment, whereas only 8, 10, 15 and 22 days of solarization were needed for the loss of viability of D. necatrix at the same depths in the second experiment. In shaded areas, however, soil solarization attained significant effectiveness at 15cm depth.Regression analyses of fungal viability (ln-transformed data) over accumulated temperature–time showed best fits when the minimum threshold temperature was 30°C. Although eradication of D. necatrix in soil can be achieved down to 60cm depth in solarized plots, and at 15cm depth in unsolarized unshaded plots, the accumulation of temperature–time appeared less effective in reducing inoculum viability in the latter.