Abstract
During winter, the causal fungus of brown leaf spot of Humulus scandens, Pseudocercospora humuli (Hori apud Takimoto) Guo et Liu, was observed in the form of conidia and stroma on fallen diseased leaves. These conidia maintained high germinability at every time examined. Although most of the conidia had disappeared by April, numerous new conidia were soon produced on new stroma in early May. Therefore, some overwintered conidia and newly produced conidia on fallen diseased leaves may act as the primary infection source on newly germinated host plant. Mycelia grew at 10°C-30°C with an optimum of 25°C. They grew well on various natural agars, such as PSA, MA and CMA and poorly on Czapek's, Waksman's and Richard's agar composed of inorganic chemicals without sugar. Among the media tested, PSA was the most suitable for mycelial growth. Mycelia grew well at a pH range from 4 to 9, but quite poorly below pH 3. Effect of fungicides and herbicide on germination of conidia and mycelial growth was tested. Although both maneb and CuSO4⋅5H2O suppressed conidial germination and mycelial growth, maneb was more effective. Meanwhile, conidia germinated and mycelial growth was not sensitive to glyphosinate at practical concentrations. Sporulation experiments on agar media were not successful.
