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 d etermine the effectiveness of soil solarization on reducing the population of D. necatrix colonizing avocado root segments buried at a depth of 15-60 cm. Increase of maximum hourly temperatures attributable to soil solarizati on reached, depending on depth, 6.7-4.6 degrees C in unshaded areas and 3.9 -1.5 degrees 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 de grees C, depending on depth) when solarization was conducted in unshaded ar eas. One, 4, 5 and 6 weeks of solarization were required to eliminate the v iability of D. necatrix at 15, 30, 45 and 60 cm depths in the first experim ent, 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 experime nt. In shaded areas, however, soil solarization attained significant effect iveness at 15 cm depth. Regression analyses of fungal viability (ln-transformed data) over accumula ted temperature-time showed best fits when the minimum threshold temperatur e was 30 degrees C. Although eradication of D. necatrix in soil can be achi eved down to 60 cm depth in solarized plots, and at 15 cm depth in unsolari zed unshaded plots, the accumulation of temperature-time appeared less effe ctive in reducing inoculum viability in the latter.