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

F. Wang, B.A. Summerell, D. Marshall and B.A. Auld

Abstract

The identity, biology and pathology of a Phaeoramulariasp. 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 244°C during and after the dew period. The use of Phaeoramulariasp. as a mycoherbicide on A. adenophora has some potential if high inoculum concentrations are used and young plants are sprayed in moist warm conditions.

Australasian Plant Pathology 26(3) 165 - 172 (1997) doi:10.1071/AP97027