STUDIES ON PROGRESS AND MANAGEMENT OF CORYNESPORA LEAF SPOT OF COTTON UNDER HIGH DENSITY PLANTING SYSTEM
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Date
2023-12-18
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Acharya N G Ranga Agricultural University
Abstract
The present investigation was undertaken to study the progress and
management of C orynespora leaf spot of cotton under High Density Planting System. On infected cotton leaves initially, minute pinhead size light orange to brick red minute spots appeared that gradually enlarged and became circular to oval or irregular concentric spots with tan to light brown centre with yellow halo around the margin. These spots enlarged and concentric zonations were formed resulting in target board symptom.
When a roving survey was conducted in cotton growing areas of Guntur district at square initiation stage, boll initiation stage and boll maturity stage for occurrence of C orynespora leaf spot mean PDI was recorded as 13.33 at square initiation stage, 20.23 at boll initiation stage and 25.25 at boll maturity stage. At RARS, Lam, Guntur highest PDI was noticed in cotton cultivar L 1060 at boll formation and boll development stage i.e., 41.25.
Multiple regression analysis of Corynespora leaf spot PDI data with weather parameters during kharif 2020-21 revealed that in all the four different spacings of HDPS tested, significant negative correlation was observed between disease severity and RH II, WS and Evap. Area under disease progress curve (AUDPC) was assessed for different spacings. Among the four spacings highest AUDPC was found in 60 cm X 30 cm (645) while the least AUDPC was observed in 75 cm X 45 cm spacing at boll maturity and bursting stage (585).
When 150 cotton germplasm lines were screened for resistance against Corynespora leaf spot, 69 entries scoring less than 10% at boll formation and boll development stage were considered resistant.
Among the eleven fungicides tested in vitro, the fungicides hexaconazole @ 0.2%, carbendazim @ 0.1%, fluxapyroxad + pyraclostrobin @ 0.06% and metiram + pyraclostrobin @ 0.3% completely inhibited the growth of the pathogen with maximum inhibition of mycelial growth (100%) and significantly superior over all other treatments. Propiconazole @ 0.1% also significantly reduced the radial growth (0.9 cm).
Under field conditions all the test fungicides significantly reduced the disease in all spacings when compared to control. After final spray maximum reduction of disease was recorded with fluxapyroxad + pyraclostrobin @ 0.06% (14.3 mean PDI) when compared to control (34.1 PDI) while highest mean PDI was recorded in carbendazim @ 0.1% (22.3). Highest benefit:cost ratio was obtained with propiconazole @ 0.1% i.e., 3.00.