Abstract
A recent survey of cocoa growing areas in India revealed that cocoa stem canker caused by Phytophthora is a serious problem. With the expansion of cocoa growing and the increase in canker incidence it became imperative to develop ecofriendly and economically viable disease management strategies. Field trials were laid out for two years to develop disease management strategies for stem canker of cocoa. There were six treatments with three fungicides viz., mancozeb, copper oxychloride and phosphorous acid, a biocontrol agent, Trichoderma harzianum and cultural practices alone. The treatments were applied only once during December. Though the different treatments except control did not vary significantly, phosphorus acid treatment was found to be better than all other treatments in controlling the disease. The number of active lesions 5 months after the treatment with phosphorous acid and T.harzianum did not vary much. Phosphorous acid (Akomin 40 @ 5ml/L. water) was applied to the wound caused after removing the bark from the canker lesion as well as spraying the whole plant. Coir pith cake seeded with T.harzianum (activated by soaking in water) was applied to the area where only 25cm2 bark surface layer was removed. In addition, five T.harzianum cakes soaked in water were kept at equidistance in the soil around cocoa plants at a distance of 15 cm from the base of the stem and covered with dried leaves of arecanut and cocoa as mulch. Luxurious growth of T.harzianam covered the entire cake after 48 h and had spread to the infected internal tissue. Removal of infected tissues from the canker (cultural practices alone) without any other treatment was also found to be effective in reducing lesion size to some extent. But the number of active lesions after 5 months of this treatment was much higher than all other treatments. Though all the treatments were on par and significantly different from the control, treatment with T.harzianum is expected to be more effective in the long run as the number of active lesions after treatment was less and because this biocontrol agent can survive and multiply under the congenial microclimatic conditions in the garden, thereby suppressing the Phytophthora population in the cropping system.
