Three leaf speckle diseases of the banana in Queensland

Abstract

Leaf speckling diseases of the banana caused by Chloridium musae Stahel, Ramichloridium musae Stahel and Mycosphaerella musae (Speg.) Syd. are described. The first two diseases appear to be confined to the tropical north of Queensland where they are present as relatively superficial leaf blemishes in rain-forest plantations or on native bananas. Mycosphaerella speckle, however, causes serious damage in plantations in Queensland and New South Wales. A conidial stage of M. musae has not yet been found. The disease is disseminated by ascospores ejected from perithecia in the dead leaf tissue. Germination takes place on the lower surface of the leaves. After a lengthy period of epiphyllic existence, at least 5-6 weeks, appressoria are formed and the fungus penetrates the leaf through the stomata on the under-sides. In experiments with protectant fungicides, Mycosphaerella leaf speckle was controlled by a single application of either copper oxychloride or zineb to the lower surfaces of leaves not showing visible symptoms. Other sprays which controlled Mycosphaerella speckle when applied to the under-sides of the leaves were white oil emulsion, white oil emulsion/malachite green, phenyl mercuric chloride and a straight paraffin oil. Treatments applied to the upper surfaces of the leaves were ineffective. Tests with eradicant sprays showed that sodium pentachlorphenate almost completely inhibited ascospore discharge when sprayed onto the lower surfaces of dead leaves containing
mature peritbecia.