P.W. Alahakoon, N.H. Jayawardene, K.C. Madushani and R.K. Nilmini
Fruit Crop Research and Development Center, Department of Agriculture, Horana, Sri Lanka
Powdery mildew of Rambutan (Nephelium lappaceum) incited by the fungus Oidium nephelii attack young leaves, flowers and immature fruits which become discolored and dry off causing fruit quality deterioration and heavy fruit losses. Oidium nephelii is controlled by application of fungicides. According to the Department of Agriculture recommendations, spraying of wettable sulphur, Chlorothalonil or Thiophanate methyl were recommended to control the disease.
Although the chemical application is the most common conventional means to control fungal diseases in crops, it is also a well known fact, that chemical control creates a lot of problems in humans and other organisms as well as it degrades the environment. Therefore new environment safe technologies should be introduced to replace the existing harmful ones. Use of biofungicides like plant extracts to control plant diseases are one of them.
An experiment was conducted at Fruit Crop Research and Development Center, Horana, to study the efficacy of herbal extracts compared with the Department of Agriculture recommended fungicides to control powdery mildew disease of Rambutan. The treatments consisted of six herbal extracts (Neem oil, Citronella oil, Cinnamon leaf extract, Clove leaf extract, Neem seed extract, Vinegar) and two recommended fungicides: Thiovit (wettable sulphur) and Daconil (chlorothalonil). Rambutan needs a critical dry period for flowering and to fruit set. Severity and spread of powdery mildew basically depends on the environment. The change in the weather pattern was to blame for the inability in the control of powdery mildew. In the past years, flowering and fruit set occurred during heavy rain conditions. Therefore selection of herbal extracts was done during heavy rain and in dry weather condition.
The results obtained from the experiment revealed that under the dry weather condition, the maximum number of healthy fruit set at harvest was given by the Citronella oil and Neem oil. The Clove leaf extract and Cinnamon leaf extract significantly controlled the powdery mildew disease and increased the healthy fruit production than that of the recommended fungicides. Neem seed extract and Vinegar controlled the disease similar to the Department recommended fungicides. In contrast to the data obtained under dry weather condition, in the heavy rain conditions, only the Citronella oil and Neem oil moderately increased the healthy fruit set at harvest while other plant extracts and all Department recommended fungicides failed to control the powdery mildew disease. Since in the dry weather condition, (normally flowering and fruit set season) plant extracts Neem oil, Citronella oil, Clove leaf extract, Cinnamon leaf extract controlled the disease than that of recommended fungicides, they can be used as the bio-fungicides. Bio- fungicides are eco friendly and are not known to cause pollution to climate or soil. Therefore it needs to be applied to reduce the degradation of environment, increased crop yield and better food safety.