EFFICACY OF REHABILITATION METHODS ON CITRUS CANKER DISEASE IN NORTHERN UGANDA

Citrus (Citrus sinensis) is an important crop in Uganda, where it is produced for both domestic consumption and regional markets. Unfortunately it is increasingly devastated by canker disease. Several measures are often recommended for citrus canker management worldwide; the major ones being orchard inspection, quarantines, protective copper sprays and the on-site burning of infected trees. The adoption rate for these options in Northern Uganda has not been possible and as a result, the disease has reached epiphytotic level. Cultural practices and phytosanitary measures, consisting of removal of inoculum sources, timely application of protective chemical sprays and field sanitation could restore citrus orchards in areas affected by citrus canker. This study was carried out to determine the most effective method of eliminating inoculum sources and appropriate chemical sprays after inoculum suppression, to prevent re-infection. On-station trials were carried out in three fields (orchards), with 90-100% of trees infected at the beginning of the experiment. Treatments evaluated were: (i) bark horning during the dry season, (ii) bark horning during the wet season, and (iii) protective copper sprays. Each orchard was divided into three portions and each portion consisted of a minimum of 10 trees. For each orchard, one portion received bark horning treatment during the wet season (November) and the other portion during the dry season (December). The third portion was treated with 0.2% copper oxychloride. Inspection and removal of twigs emerging with symptoms two months after bark horning treatment, application of protective copper and insecticide sprays two, three and four months after bark horning were administered as a follow up treatments to bark horning. The effect of treatments on citrus canker incidence was significant (P 0.05). The incidence of re-infection was highest in plots that were bark horned during the wet season (23.4%), and lowest inplots bark horned during the dry season (3.3%). Complete bark horning of infected orchards at the beginning of dry season, followed by at least 6 months of regular orchard inspection; removal of re-infected branches and judicious application of chemical sprays (copper oxychloride fungicide and pyrinex insecticide) was the best option for managing citrus canker disease. Use of cultural practice and phytosanitary measures is, hence, recommended.