EPIDEMIOLOGY AND MANAGEMENT OF ALTERNARIA LEAF SPOT OF CABBAGE
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Date
2015
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ABSTRACT
Alternaria leaf spot caused by Alternaria brassicicola (Schw.) Wiltsh. is one of the major disease of cabbage in wet temperate areas of Himachal Pradesh. Survey studies conducted in the present investigation revealed that the disease occurred in moderate to severe form in different cabbage growing localities of Shimla, Solan, and Sirmour districts of Himachal Pradesh. Temperature of 20±1°C was found optimum for symptom development and the relative humidity 95±5 percent with 16 h of leaf wetness period favoured the disease development most under controlled conditions. The sporulation of Alternaria brassicicola was observed to be favoured most at temperature 20-30ºC and relative humidity ≥90%. The epidemiological studies conducted under field conditions revealed that wet and humid conditions coupled with moderately low temperature favoured the rapid Alternaria blight disease progression. Survival studies suggested that the survivability was greater in stem debris than in leaf debris and the pathogen recovered in considerable proportion in stem plant debris even after seven months storage period. The in vitro evaluation of fungicides indicated Cabriotop (metiram 55% + pyraclostrubin 5% WG), Indofil Z-78 (zineb 75% WP) and Captaf (captan 50% WP) as potent growth inhibitor of Alternaria brassicicola while amongst the botanicals, garlic and neem extracts were most promising. Amongst the different fungal antagonists evaluated in vitro conditions, Trichoderma harzianum proved most inhibitory to Alternaria brassicicola while testing their antagonistic efficacy through dual culture or through volatile substances. The integrated management studies conducted under field conditions revealed that treatment combination consisting of soil application of Trichoderma harzianum @ 2.5 kg/50kg FYM/ha and mulching with black polythene sheet in combination with four periodic spray of zineb @ 0.2% at 10 day interval proved most efficacious in limiting the Alternaria leaf spot disease and enhancing the yield.