MSc.

The present investigation on “Management of leaf spot diseases of arecanut (Areca catechu L.)” was conducted at the Department of Plant Pathology, College of Agriculture, Vellayani, during 2011-2013. The objectives were to study the leaf spot diseases affecting young areca palms and to develop an integrated management practice to contain the diseases.
Three pathogens were obtained from the leaf spots. Pestalotiopsis palmarum Cooke. was isolated from dark brown or grey spots with brown bands and it produced white cottony mycelium with black coloured fruiting bodies on PDA. Colletotrichum gloeosporioides (Penz.) Penz and Sacc. was isolated from brown spots with yellow halo and also from grey spots without any margin and it produced dense, cottony, dirty white to greyish mycelium with pinkish conidial mass on PDA. Phomopsis palmicola was obtained from round to oval brownish spots, mycelium on the PDA was dull white, flat mycelial growth with even margin. All the cultures were molecularly characterized and identified as P. palmarum, C. gloeosporioides and P. palmicola based on the sequences obtained amplification of the ITS regions and diversity was observed in the sequences of the isolates from different geographical locations. Among the different pH levels, maximum radial growth of P. palmarum and C. gloeosporioides was observed at pH 5.0.
Disease occurred in all the locations surveyed and PDI of 34.5 was present in I.F. Vellayani. Incidence ranged from 75-85 per cent and the disease was restricted to 3-4 basal leaves only. Correlation coefficient between PDI and weather parameters showed that minimum temperature had significant negative correlation (-0.6725) with PDI. Five fungal and two bacterial organisms were isolated from phyllosphere and rhizosphere of healthy areca palms and one fungi and two bacteria were showing antagonistic activity against the pathogens.
In vitro evaluation - T. harzianum was effective in inhibiting the growth of P. palmarum (62.77%), C. gloeosporioides (51.04%). Out of the seven fungicides evaluated Propiconazole at (0.075, 0.037, 0.018%) and Carbendazim (0.2, 0.1, 0.05%) completely inhibited the growth of P. palmarum and C. gloeosporioides. Among five botanicals tested garlic at (2, 4 and 6%) was effective on P. palmarum and C. gloeosporioides. Garlic at 6% and azoxystrobin at 0.1% were compatible with T.harzianum upto 82.21% and 72.09% respectively. All other systemic fungicides tested were completely incompatible with the biocontrol agent.
An experiment was conducted with eight treatments and one control on seedlings in the green house. All the treatments tested were significantly effective against leaf spot diseases of arecanut. After 30 days of second spray the most effective treatment was Carbendazim with 50.15 % reduction in PDI, which was on par with Propiconazole which recorded 48.61 % and Difenoconazole with 48.29%.
For field level the experiment was conducted with eight treatments and one control on 4-7 yr. old young areca palms in the Instructional Farm, Vellayani. All the treatments tested were significantly effective against leaf spot diseases of arecanut. After 30 days of third spray the most effective treatment was Carbendazim with 39.33 % reduction in PDI which was on par with Propiconazole which recorded 38.90 % reduction. These two treatments were significantly superior over all other treatments, followed by combination treatment Azoxystrobin + T.harzianum which had 29.36 % reduction in PDI over control and pre- treatment.