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Reduction % (0-30 cm): 15 days after: 77% 30 days after 56% S, Solarized; NS, Nonsolarized CFU, colony-forming units. Source: Panayanthatta (1997).

Reduction % (0-30 cm): 15 days after: 77% 30 days after 56% S, Solarized; NS, Nonsolarized CFU, colony-forming units. Source: Panayanthatta (1997).

Cook et al., 1987; Vilasini, 1996; Panayanthatta, 1997). Panayanthatta (1997) has determined the inoculum density of P. aphanidermatum for 3 years in solarized and non-solarized soils at three depths (Table 8.3). The inoculum density on the 15th day after tarping was 41.66 colony-forming units (CFU)/g of soil in solarized plots compared to 166.66 CFU/g of soil in nonsolarized plots at 0 to 10 cm depth; 33.33 CFU/g and 191.66 CFU/g at 10 to 20 cm depth and 8.3 and 8.2 CFU/g of soil and 20 to 30 cm, respectively.

If solarization is done properly, it enhances the soil temperature from 37 to 52°C, which is sufficient to kill most pathogenic fungi (Katan et al., 1976; Katan, 1981). The thermal inactivation point of Pythium species is between 37 and 50°C. In P. ultimum, for example, the LD90 is achieved in 17.9 days at 37°C and 33 minutes at 50°C (Pullman et al., 1981). Soil solarization also set the soil for increased activity of antagonistic organisms (Katan et al., 1983). Rapid colonization of solarized soil by antagonistic Trichoderma has been demonstrated (Elad et al., 1980). Solarization is an important component of integrated disease management. Panayanthatta (1997) obtained a reduction in the rhizome rot incidence as a result of soil solarization (Table 8.4).

Chemical Control: Various types of seed treatments with different chemicals have been tried by various workers to kill the rhizome-borne inoculum. Treatment of rhizomes with 0.1 percent mercuric chloride for 24 hours (Park, 1935) or 90 minutes (Thomas, 1941; Kothari, 1966), Ceresan (0.25 percent) (Thomas, 1940; Anonymous, 1953), and Agrosan-GN (0.25 percent) treatment for 30 minutes are effective against rhizome rot (Thomas, 1941). Simmonds (1958, 1959) controlled the rhizome rot caused by Fusarium oxysporum by 10-minute immersion of rhizomes in standard mercurials at 2 lb/40 gal.c Mathur et al. (1985) controlled rotting caused by P. aphanidermatum and F. solani with the help of Bayleton (triadimefon). Other fungicides tested, such as Fenaminosulf, Difolatan (captafol), Syllit (dodine), and Ridomil (metalaxyl), were also effective. Chemicals such as Antracol (propineb, 0.25 percent), Fycop and Blitox-50 (copper oxychloride, 0.3 percent) are also effective in the control of rhizome rot (Dohroo and Sharma, 1986).

Table 8.4 Effect of soil solarization on disease incidence and yield (3 years average)

Treatment

Germination (%)

Disease incidence (%)

Yield per 3 m2 bed (kg)

Solarized

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