Experiences in managing Bacterial Dieback Disease of Papaya in Malaysia

Bacterial Dieback Disease (BDB) caused by Erwinia papaya was first recorded in Malaysia in 2003 and has since obliterated most of the papaya farms in the country. All commercial cultivars are susceptible and management practices by farmers have not been proven successful so far in managing this disease. Our observations are that the bacterium typically enters the host through wounds, and passes through the petiole into the green stem. The segment of the petiole attached to the lamina subsequently dries up and rots, resulting in a hanging leaf or ‘flag-leaf’ symptom. The area on the green stem around the diseased petiole often shows dark water-soaked streaks or lesions, and in severe infections the crown of the tree gradually withers and the tree collapses and dies within four to eight weeks. The Malaysian Agrifood Corporation Berhad (MAFC) had established a large papaya farm in Lanchang, Pahang in December 2006. The farm was initially disease-free and therefore a ‘BDB exclusion programme’ was imposed whereby traffic and visitors were restricted in entry to the farm. Those permitted entry were sanitized with shoe-dips and disinfectant tyre sprays. Despite these measures, BDB was detected in the farm in late 2009 requiring that a ‘BDB containment programme’ be initiated. An intensive surveillance programme to detect diseased plants was established, and all trees with mild symptoms had their diseased parts (leaves or fruits) promptly removed. Trees with severe infections are cut back to a meter from the ground and allowed to re-shoot. For the most serious infections, the whole tree including the root is removed and Calcium carbonate is sprinkled around the diseased area and copper fungicides are sprayed around the trees in the vicinity to help reduce spread. This paper discusses the disease dynamics, thresholds and some of the recent control measures being evaluated for prevention and mitigation of BDB, including thermal surgical treatment and the use of antibacterial compounds.