November 26, 2022 09:22 pm |Updated 09:22 pm IST - MANGALURU
The leaf spot disease which has hit arecanut plantations, mainly in five districts of the coastal and the Malnad regions. | Photo Credit: SPECIAL ARRANGEMENT Methomyl Insecticide
The leaf spot disease which has hit arecanut plantations, mainly in five districts of the coastal and the Malnad regions, in the State can be effectively controlled by adopting community based spraying approach, according to P. Chowdappa, former Director, Central Plantation Crops Research Institute (CPCRI), Kasaragod, Kerala.
“The severe epidemics of leaf spot caused by fungus Colletotrichum was recorded in arecanut since 2021 even though the disease was reported in 1977 as inflorescence dieback and leaf spot in 1993,” he told The Hindu.
Mr. Chowdappa said that the longer duration of the rainfall this year could be one of the reasons for the disease spreading fast to a vast tracts of arecanut. If not, new variants of the fungus might have also attacked arecanut. Usually the severity of the disease comes down in the summer and it can reappear in the prolonged wet condition if control measures are not taken in the disease hit plantations before the onset of monsoon.
“C. gloeosporloides, has been reported as the causal agent of the leaf blight and inflorescence dieback of arecanut in India. However, seven Colletotrichum species such as C. cordylinicola, C.fructicola, C.gloeosporioides, C.siamense, C.tropicale, C.arecicola and C.karstii have been found to be associated with arecanut leaf spot in Hainan region of China,” he said.
The former Director said that epidemics caused by Colletotrichum species generally occur in rainy, humid, and warm weather, with temperatures ranging between 20°C and 30°C and spread through water splash and wind.
The disease appears as a small round/ellipitical light to dark brown spots surrounded by dark brown margins and yellow halo on leaves, sunken spots with concentric rings on fruits and dieback symptoms on inflorescence.
Through the spray of Bordeaux mixture before the onset of monsoon followed by spray of new generation mixture of fungicides can effectively control the disease. “Community based spraying approach by government agencies using unmanned aerial vehicle should be adopted for effective management,” the scientist said, adding that if the disease is noticed in a particular plantation in an area owners of other plantations in the same area should take up spraying to control its spread.
Mr. Chowdappa said that Colletotrichum disease outbreaks have also been recorded on many horticultural crops in the country during last two years. It included onion, chillies, capsicum and grape. The disease has also been reported on golden cane palm (Chrysalidocarpus lutescens) in Gujarat.
“These outbreaks occurred despite use of chemical control measures, probably due to increasing prevalence of fungicide resistance or changes in population structure or prevalence of favourable weather conditions over a relatively long period of time,” he added.
H.R. Nayak, Deputy Director, Department of Horticulture, Dakshina Kannada, who was a member of a Central (scientific) study team which visited leaf spot disease hit arecanut plantations across the State for three days recently (from November 20, 2022) told The Hindu that the disease has not been noticed in Bayaluseeme area in the State.
He said the disease hit leaves should be cut from the arecanut palm and burnt down as a safety measure.
The extent of area hit by the disease is being collated. The team will submit its report both to the State and Central government shortly, he said.
Mr. Chowdappa said that spraying fungicide is one of the main strategies to control areca leaf spot disease. However, different Colletotrichum species display different sensitivities to individual fungicides. Multisite protectant fungicides like manozeb, thiram, ziram, captan and chlorothalonil have historically provided good efficacy against Colletotrichum diseases.
However, longer wetter season and changes in pathogen population has necessitated the incorporation of systemic fungicides. The systemic fungicides like carbendazim, thiophanate- methyl, fenbuconazole, metconazole, propiconazole, benzovindiflupyr, penthiopyrad, azoxystrobin, fluoxastrobin, pyraclostrobin, trifloxystrobin and polyoxin D, which have been reported to be medium to high levels of risk of resistance, may have limited use in disease management.
New generation of mixtures of single site and multi=site fungicides such as carbendazim+ mancozeb (2g/l), zineb+hexaconazole (2g/l), flusilozole+ carbendazim (2ml/l), fluopyram+tebuconazole(1ml/l),azoxystrobin+tebuconazole(1ml/l),fluxapyroxad+difenconaz ole (1.2ml/l), tebuconazole (1ml/l)+ propineb (2g/l), fluxapyroxad+pyriclostrobin (0.5ml/l),pyriclostrobin +metiram( 1.5g/L) are to be used.
Comments have to be in English, and in full sentences. They cannot be abusive or personal. Please abide by our community guidelines for posting your comments.
Tafgor Dimethoate We have migrated to a new commenting platform. If you are already a registered user of The Hindu and logged in, you may continue to engage with our articles. If you do not have an account please register and login to post comments. Users can access their older comments by logging into their accounts on Vuukle.