Stenocarpella maydis

Abstract

DISTRIBUTION: One of the most prevalent moulds on harvested maize throughout the world. Diplodia ear rot is caused by the fungus Diplodia maydis. Maize is produced mainly in the North-West, the north-western, northern and eastern Free State, the Mpumalanga Highveld and the Kwazulu-Natal midlands.

BOTANICAL DESCRIPTION: General: It is a phytopathogenic fungus that causes i.a. stalk rot and cob rot. Conspicuous coarse, white to grey mycelium, resembling toothpaste.

The fungus overwinters as mycelium, spores, and picnidia on corn residue or seed. Primarily splashing rain spreads the spores. Infections first appear at the base of the ear. Corn borer damage in the shank can provide an entry wound for the pathogen. Diplodia is favoured by cool, wet weather during grain fill.

This fungus initially appears as a white mould beginning at the base of the ear. The mould and the kernels eventually turn a greyish brown colour and rot the entire ear. The mould may be apparent on the outside of the husk or on the shank. A distinguishing characteristic of Diplodia ear rot is the appearance of raised black bumps on the moldy husk or kernels. These are the picnidia of the fungus, where new spores are produced.

TOXIC PRINCIPLE: Unknown neurotoxin.

SYNDROMES: Diplodiosis.

SYSTEMS AFFECTED : Central nervous system.

CLINICAL SIGNS: A neurotoxicosis of cattle and occasionally sheep on harvested maize fields in winter. In cattle • salivation, • wide-base stance, • tremors, • ataxia, • incoordination, • stiffness, • high-stepping gait and • paresis/paralysis are observed.

NECROPSY: • Nothing specific.