Control of phytoplasma diseases of papaya in Australia using netting

Three types of netting material (coarse, medium and fine mesh) were evaluated for exclusion of insects and thus control of phytoplasma diseases (especially dieback disease) of papaya. Disease incidence and yield parameters were recorded for a population of papaya plants grown inside netted enclosures, each 20 m long by 12 m wide by 5 m high, containing 78 planting positions. A further population of non-netted plants was treated with a systemic insecticide (imidacloprid). Six percent of control plants and insecticide-treated plants died with dieback symptoms. No plants under fine or medium mesh net were affected by dieback, but one plant under the coarse mesh net developed symptoms. The incidence of other disease and damage (e.g. yellow crinkle disease, fruit spotting bug damage) was also decreased in netted plants. However, pollination was poor under netting, with individual fruit weight and total harvested fruit weight reduced to ~50% of that of the control. Fruit sweetness (total soluble solids) was not affected. Management issues and cost-effectiveness of using netting as a control strategy are discussed. It is concluded that netting is not a commercially viable strategy with current production and marketing methods, although it could be used as part of a higher value, more intensive production system