Economically important diseases of maize

Maize is considered the most important grain crop in South Africa, thus there are various maize diseases that farmers need to be on the lookout for. Janine Ryan reports on some of the most dominant of these diseases.

- Janine Ryan

NORTHERN CORN LEAF BLIGHT

Northern corn leaf blight is one of the most common diseases of maize in South Africa, and while yield losses are typically minimal, they can become significant if the planted cultivar is susceptible.

The disease is caused by the fungus Exserohilum turcicum, and generally occurs before silking. It prefers moderate temperatures (around 18°C to 27°C) with prolonged periods of moisture. The fungus overwinters on maize leaf debris.

The University of Minnesota Extension (UME) says that the disease is usually more severe when infection occurs earlier.

FAST FACTS

Maize streak disease can cause stunting of maize plants and misshapen cobs.

Northern corn leaf blight can result in significant yield losses.

Grey leaf spot thrives in areas with warm temperatures and prolonged periods of high humidity (greater than 95%).

SIGNS AND SYMPTOMS

The UME says that typical symptoms of northern corn leaf blight are canoe-shaped lesions that range from 2,5cm to 15cm in length.

Initially, these lesions may be bordered by grey-green margins, which eventually turn tan colour and may contain dark areas of fungal sporulation.

The length or size of lesions may vary with different [maize] hybrids, the UME explains. Lesions generally begin on the lower leaves, before spreading to the upper leaves. Symptoms can progress rapidly, resulting in blighted leaves.

ESSENTIAL FACTS

• Pathogen: Exserohilum turcicum

• Typical signs and symptoms: canoe-shaped lesions, which are initially bordered by grey-green margins.

• Preferred conditions: moderate temperatures and high levels of humidity.

• Effects: yield losses.