M Sc.

The study entitled “Management of Cercospora leaf spot of vegetable cowpea Vigna unguiculata subsp. ungiculata (L.) Verdcourt) was undertaken at the Department of Plant Pathology, College of Agriculture Vellayani and Coconut Research Station, Balaramapuram during 2015-2017 with the objective to study the symptomatology and etiology of Cercospora leaf spot of cowpea and to develop a management strategy.
Symptomatology and etiology of Cercospora leaf spot disease was studied during the flowering or pod bearing stage of the crop from different locations near to College of Agriculture, Vellayani. Symptoms were observed on the leaves, pods and stem .Conidial dimension of the pathogen ranges from 24.64 to 57.6 µm x 1.06 to 2.7 µm and the conidial septation was around 10 to 18. Based on the conidial and mycelial characters, the pathogen was tentatively identified as Cercospora sp. The identity of the pathogen was further confirmed based on the morphological characteristics and the herbarium specimen send to National Fungal Culture Collection of India, (N.F.C.C.I), Pune as Pseudocercospora sp. aff. Pseudocercospora vignigena (F: Mycosphaerellaceae)
In vitro pathogen suppression by spore germination assay revealed that the fungicide difenoconazole (0.1%) recorded 42.96 per cent reduction over control and was followed by propiconazole (0.1%) and hexaconazole (0.1%) which recorded 36.85 and 31.10 per cent reduction over control, respectively. The organic formulations, mineral oil (0.1%) and neem oil (0.5%) recorded only 21.88 per cent reduction over control and were statistically on par .KAU talc based formulation of Pseudomonas fluorescens at 2.0 % recorded 11.88 per cent reduction of spore germination over control.

The pot culture studies conducted using eight best treatments (difenoconazole (0.1%), propiconazole (0.1%), hexaconazole (0.1%), carbendazim (0.05%), azoxystrobin (0.05%), mineral oil (0.1%) neem oil (0.5%) and P. fluorescens 2.0 %) selected from in vitro studies revealed that the foliar spray of 0.1 per cent difenoconazole recorded the minimum disease incidence (23.80%) and disease severity (8.23 %) that accounts to 54.80 and 76.06 per cent disease reduction over control respectively. In the case of organic formulations, mineral oil (0.1%) recorded the minimum disease incidence (30.04%) and disease severity (16.54%). The plant sprayed with KAU talc based formulation of P. fluorescens (2.0%) recorded 33.69 % disease severity reduction over control. With regard to pod yield, the plants treated with difenoconazole (0.1%) registered the maximum (0.523 kg/pot) yield with 88.80% yield increase over control while ,the untreated control plants registered the lowest yield (0.277kg/pot).
Based on the results of pot experiment, a field study was conducted at Coconut Research Station, Balaramapuram to evaluate the efficacy of five best treatments (difenoconazole (0.1%), propiconazole (0.1%), mineral oil (0.1%) neem oil (0.5%) and P. fluorescens 2.0 %) selected from the pot culture studies. Among the fungicides, difenoconazole (0.1%) recorded the minimum (31.88%) disease incidence and disease severity (13.97%) compared to all other treatments. In the case of organic formulations, mineral oil (0.1%) gave the maximum (14.32%) disease suppression and the lowest disease incidence of 40. 57 %. With regard to yield, maximum pod yield was from the plot sprayed with difenoconazole (1620 kg /ha) followed by propiconazole (1386.5 kg /ha) treated plants. Even though, the application of P. fluorescens gave only 29.23 per cent of the disease suppression, it enhanced the yield by 52.27 per cent yield over the control.
It was concluded that foliar application of difenoconazole ( 0.1% ) at an interval of 35, 50 and 65 DAS was found to be the most effective treatment in managing Cercospora leaf spot in vegetable cowpea besides supporting proportionately attractive pod yield (1620 kg/ha) at an acceptable B:C ratio (2.44:1).Among the organic formulations, mineral oil (0.1%) was found to be the effective treatment in controlling leaf spot with a pod yield of 1293 kg/ha . While, P. fluorescens recorded a pod yield of 1318 kg/ha with B: C ratio of 2.02:1