Using pencycuron : Screening of new fungicides against rice sheath blight disease

Sheath blight of rice caused by Rhizoctonia Solani Kuhn. is regarded as one of the most widely distributed disease of rice. Its occurrence in India was reported by Paracer and Chahal (1963) from Gurdaspur in the Punjab. Sheath blight is one of the major fungal diseases of rice in Karnataka. It appears throughout the rice growing areas of the state in varying degree. The disease appears both on sheath and laminar portion of leaf. Depending upon the age of the plant, time of infection and severity, it causes yield loss to the extent of 5.9 to 69 per cent (Venkat Rao et al., 1990; Naidu, 1992). The incidence of disease has become rampant with the introduction of semi dwarf, heavy tillering, early maturing and high yielding varieties. In the absence of suitable resistance donor, chemical control is the only alternative to check this disease. Since the seriousness of disease warrants chemical protection, it is important to explore alternative chemical molecule to avoid build up of resistance in the pathogen. Several new fungicides have been recently developed which are known to possess good control against Rhizoctonia Solani. The present study was undertaken to evaluate some new fungicides against this disease. The field experiment was conducted during Kharif 2006 season at Zonal Agricultural Research Station, Mandya. The soil of the experimental site was red sandy loam, slightly acidic in nature (pH 5.9). The experiment was laid out on a randomized block design with eight treatments replicated three times. The treatment consisted of two new formulations viz., Filia 52.5 SE (tricyclazole 400 g + propiconazole 125 g) and Nativo75 WG (trifloxystrobin 25% + tebuconazole 50%) and three commercially recommended fungicides such as Hexaconzole (Contaf 5 EC), Validamycin (Rhizocin 3L) and propiconazole (Tilt 25 EC) were used as standard check. "IR 64 was used as test variety. Uniform plant population was maintained for each plot, which had 20x10 cm spacing with a plot size of 3.2x1.2 m. Sheath blight disease was artificially built up by inserting the infected bits on the rice seedlings after 38 DAP during tillering stage. Three sprays of chemical with desired concentration were given on 50th, 65th and 80th days after planting. Except for the treatments, recommended package of practices (Anon., 2006) were followed for growing the crop. Observations on disease severity and yield were collected. The data obtained were subjected to statistical analysis and were tested at five per cent level of significance to interpret the treatment differences. The data on sheath blight and yield levels are presented in table 1. Symptoms started appearing after 22 days of artificial infection. Then it approached a faster spread due to congenial atmosphere. Sheath blight severity was to the tune of 33 per cent in untreated plots. The literature review on chemical evaluation of sheath blight revealed that from time to time and place to place different chemicals have been identified . Dithane M-45 (Das and Mishra,1990), Carbendazim and Mancozeb (Thangaswamy and Ranagswamy, 1989; Roy and Saikia,1976) Iprodione (Izadyar and Baradaram, 1989) Triazole (Suryadi et al., 1989) and Carbandazim + Mancozeb (Prasad et al., 2006) were found effective. Periodical observation on sheath blight severity was recorded and presented in Fig.1. In the present study, all the chemicals tested reduced the disease considerably compared to control. The reduction in the sheath blight varied from 22 to 31 per cent in different treatments. Among the new formulatins, application of Filia 52.5 SE and Nativo 75 WG 0.4g was found equally effective in controlling the sheath blight as it controlled around 25 per cent compared to control. Among the ruling fungicides Contaf 5 EC was found very effective. It controlled the disease to the tune of 31 per cent. Application of right chemical at a right time was very important in control of sheath blight., However, the Pencycuron (Moncern 250 EC) was very effective under Punjab and West Bengal conditions (Lore et al., 2005; Biswas, 2002).
Grain yield varied correspondingly to the disease incidence. Untreated plots showed incidence of sheath blight disease thereby the crop suffered and the yield levels were 4173 kg/ha. Among different chemicals, application of Contaf 5 EC was found effective in controlling the disease with higher yield (5322 kg/ha) as compared to control, followed by Filkia 52.5 SE at different rats of spray (4936 to 5087 kg/ha). Various workers supported the higher yield due to disease control efficiency of the respective chemicals 

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