Management of taro leaf blight disease caused by Phytophthora colocasiae in the Eastern Region of Ghana

Abstract

Studies on the management of leaf blight disease on taro by Phytophthora colocasiae were conducted in the Eastern District of Ghana. The studies comprised a survey to assess the prevalence of the disease, production practices of fanners and perception of the disease in ten selected districts of the region. It also included characterisation of isolates of Phytophthora colocasiae from the ten districts and the evaluation of twenty-one taro accessions both in vitro and on the field for resistance to the taro leaf blight disease (TLBD). Five different fungicides (Carbendazim, Agro Comet, Chemoliette, Mancozeb and TOPS-M) were evaluated in vitro to determine their effectiveness against P. colocasiae as well as evaluation of different plant distances (1.0 m x 1.0 m, 0. 75 m x 0. 75 m and 0.6 m x0.9 m) for the management of TLBD. It was observed that majority of the farmers were male (75%), relatively young (< 50%) with age range of 20 to 49 years and low level of education (JHS/MSL). Most farmers produced taro on small pieces of land (0.5 acres to 1.44 acres) and in river plains as sole crop. Majority of the farmers had observed the TLBD on their farms and revealed that it mostly occurred in the rainy season and high in marshy areas with stagnant water. The results revealed that majority of the farmers used insecticides instead of fungicides to manage the disease. Few fa1mers practiced pruning as and when the disease appeared and admitted that it was very effective in managing the disease. The disease was observed to be very high in the districts with incidence of 62.2% to 92.2% in wet season and 69.9% to 78.9% in dry season with New Juabeng and Fanteakwa district recording the highest. The studies revealed that all the isolates were P. colocasiae, but showed differences in their length and width of sporangia, varying from 36 µm to 61.67 µm and 20 µm to 28 µm respectively and also a pedicel length of 3.667 µm to 12.333 µm. Amongst the 21 taro accessions evaluated, 4 exotic ones were resistant to the TLBD and only one local accession was tolerant. Carbendazim and Agro Comet (Metalaxyl + Copper (I) oxide) were identified to be most effective in reducing the growth of P. colocasiae at a rate of 300 ppm to 500 ppm. The combination of wider spacing (I.Om x I.Om and 0.75m x 0.75) and pruning reduced the severity of the disease significantly.