Solarization and fungicides for the control of drop, bottom rot and weeds in lettuce

Soil solarization was applied for 60 days during the summer in lettuce fields in Mogi das Cruzes (latitude 22°31′S, longitude 48°11′W), southeastern Brazil, from December to January, 1998/99 and 1999/2000, after which two consecutive lettuce crops were grown in each cropping season. Soil solarization was tested in association with the fungicides pencycuron and procymidone, with the purpose of controlling bottom rot and lettuce drop, caused by Rhizoctonia solani AG1-I and Sclerotinia minor, respectively. In the first crop of both years the solarized treatments presented very low incidences of the diseases and shortened the crop cycle by 10 days as compared to the non-solarized plots. In both years the incidence of lettuce drop in the second (winter) crops was very low in the solarized plots, but a 25–40% loss of lettuce heads to the disease was observed in the control plots (no solarization and no fungicides). Although the incidence of diseases in the non-solarized plots was reduced by the fungicides, they did not offer additional benefits in the solarized areas in both crops. Reductions in biomass C and in the number of fungi and bacteria were observed in the solarized treatments, but the amount of fluorescent pseudomonas was not affected by the soil treatments. The concentrations of soil nutrients NH4–N and DTPA-extractable-Mn increased sharply due to solarization. Changes in soil nutrient availability and probably in the microbial community, among other non-detected benefits, may be related to the reduction of the crop cycle in the present work.