Effect of water management on mycoherbicidal activity of Exserohilum monoceras against Echinochloa oryzicola [Echinochloa crus galli]

Factors affecting the herbicidal activity of Exserohilum monoceras JTB-808 against Echinochloa oryzicola young seedlings were examined using a drop inoculation method under greenhouse conditions. The herbicidal activity of the fungus correlated with water management practices. High herbicidal activity was produced by increasing the depth and duration of water flooding. When 10(5) conidia/100 cm2 were introduced to a pot filled with water to a depth of 7 cm or 9 cm, more than 95 % of plants were killed, and the dry weight of the plants was reduced by over 95 % at 21 days after inoculation. A water depth of 7 cm with 7 or more days of flooding gave almost the same results at 21 days after inoculation. When the flooding was prolonged to 14 days, the plants were completely destroyed. Shallow depths or short flooding duration were not effective. Lesion development under submergence was examined on the first leaf of E. oryzicola after inoculation with conidia embedded in low melting-temperature agarose gel. When inoculated leaves were kept under submergence for 1, 2 or 3 days, collapsed lesions enlarged to 14.3, 78.7 and 95.3 % of the leaf area of each sample, respectively, by 10 days after inoculation. The results show that submergence of the host plants promoted lesion development, which led to high mycoherbicidal activity