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Disease Management

Cultural Practices

Early disease management is aimed at reducing the inoculum level and relative humidity in the field. Taro leaf blight is an explosive disease, however, and cultural and physical control methods are usually ineffective during an epidemic. Roguing (removing all or parts of infected leaves) reduces inoculum levels. As disease severity and roguing intensify, however, physical leaf removal mimics the blight by further reducing total leaf surface area.

Field sanitation may decrease inoculum levels early in the season, but sporulating leaf lesions supply enough propagules (sporangia, zoospores) to increase disease. Spacing plants farther apart does little to decrease taro leaf blight disease. It has been demonstrated experimentally, both in the presence and absence of leaf blight, that planting taro closer together improves yield. Close spacing (e.g. 0.5 m or 2 ft) may increase leaf blight severity, but it also increases the total weight and number of corms, though individual corms are smaller.

Chemical Management

Protectant chemical sprays containing copper, manganese, or zinc, have been effective against taro leaf blight, but heavy rains make repeated applications necessary. Good results have also been reported with metalaxyl, a systemic agent used against the oomycetes. In many countries and island nations, however, taro is a subsistence crop and routine chemical use is neither economically practical nor environmentally suitable.

Genetic Resistance

Resistant cultivars offer the best long-term control of taro leaf blight. However, desirable cultural characteristics and eating qualities are often lost during breeding. Current breeding efforts therefore are focused on improving yield, suckering (desirable for vegetative propagation), time to maturity, taste, and texture.

Isozyme analysis and DNA markers (RAPD) have identified significant genetic differences in isolates of P. colocasiae within and between countries, which may affect the pathogenicity of the isolates. With this in mind, taro from breeding programs should be tested against P. colocasiae isolates already present in countries before new breeding lines are introduced.