Biology and pathology of a species of Phaeoramularia causing a leaf spot of crofton weed

The identity, biology and pathology of a Phaeoramularia sp. isolated from crofton weed, Ageratina adenophora, were investigated to assess its potential as a mycoherbicide for control of crofton weed. Leaf infection by A. adenophora by a conidial suspension of Phaeoramularia sp. was studied using light and electron microscopy. Under optimum conditions, Phaeoramularia sp. could penetrate leaves via stomata 5 days after inoculation and express leaf-spot symptoms and produce conidiophores on the leaf surface within 7 days. An investigation of various host and environmental factors showed that the optimum conditions for infection of seedlings of crofton weed with Phaeoramularia sp. were an inoculum concentration of 106 conidia/mL, a dew period of at least 18 h and a temperature of 19 to 24°C during and after the dew period. The use of Phaeoramularia sp. as a mycoherbicide on A. adenophora has some potential if high inoculum concentrations are used and young plants are sprayed in moist warm conditions.