Reductions in Inoculum Density ofRhizoctonia solaniand Control of Belly Rot on Pickling Cucumber with Solarization

Abstract

The effectiveness of soil solarization to reduce the level of Rhizoctonia solani in soil and control belly rot on cucumber fruit was evaluated in naturally infested soil. Solarization under clear polyethylene mulch for 5 to 6 weeks during July and August 1992 to 1994 was compared with application of chlorothalonil and no treatment in a randomized complete block design. During solarization in 1993 and 1994, the percentage of organic matter colonized by R. solani declined at 0 to 10 cm depth in solarized soil but did not change significantly in nonsolarized soil. After solarization, colonies of R. solani grew from 0.9, 7, and 2.8% of the organic matter fragments recovered from solarized soil in 1992, 1993, and 1994, respectively, compared with 23, 44, and 26% of the organic matter from nonsolarized soil. Population densities of fluorescent Pseudomonas spp. at 0 to 20 cm declined during solarization each year. In 1992 and 1994, thermotolerant fungi, which grew at 40°C, were more abundant in solarized than nonsolarized soil. Penicillium spp. accounted for a significantly greater percentage of thermotolerant fungi in heated than in nonheated soil each year. Solarization reduced belly rot severity on pickling cucumber in 1992 and 1994 compared with no treatment (4.8% versus 10.1% and 4.4% versus 12.9%, respectively), whereas chlorothalonil reduced severity in 1993 (4.0%) and 1994 (4.1%). Incidence of belly rot was reduced by solarization and chlorothalonil applications in 1993 and 1994 but not in 1992. Neither treatment significantly increased total weight of healthy fruit compared with the control. In 1994, healthy fruit in solarized plots had a higher market value than fruit in plots of the other two treatments, but after cost of the treatments was subtracted, returns did not differ. Soil solarization is an effective nonchemical method for reducing preplant levels of R. solani.