Effectiveness of soil solarization against soil-borne plant pathogens and weeds in Piedmont (northern Italy)

Soil solarization was tested during a period of eight years as a disinfestation method on soil naturally infested by Rhizoctonia fragariae (1990-1992), Verticillium dahliae (1993-1997) or artificially inoculated with Fusarium oxysporum f. sp. melonis r 0 (1998-1999), and weeds (1993-1997) under polyethylene tunnels, in the environmental conditions of the Piedmont Po Valley, a region so far considered as climatically marginal for its use. The effects of the closed tunnel, without soil mulching (semi-solarization) were also evaluated. Soil treatments were performed during July and August for a period of 45 days. At 15 and 25 cm of depth, the solarization caused a soil thermal increase of 15.4 +/- 2.7 degreesC and 14.7 +/- 1.84 degreesC and the semi-solarization of 9.4 +/- 1.02 degreesC and 9.0 +/- 1.26 degreesC respectively. The soil solarization delayed the appearance of all the tested diseases and reduced the incidence of strawberry Rhizoctonia root rot by 68 - 75%, eggplant Verticillium wilt by 89-96 %, melon Fusarium wilt by 94.6% in 1998 and 59% in 1999. The semi-solarization partially controlled V, dahliae. The improved plant health constantly gave rise to statistically significant yield increases in quality and quantity. The semi-solarization treatment significantly reduced the total weed population in 2 trials out of 4, showing a good effectiveness against Chenopodium polyspermum, Galinsoga parviflora, Stellaria media and Solanum nigrum, but not against the monocots. Soil solarization reduced the number of weeds by 66% in 1994 and by 97% in 1995, 1996 and 1997; it was effective against all species of weeds, but Portulaca oleracea appeared to be quite resistant.