African maize stalk borer

The African maize stalk borer (Busseola fusca) is a moth species in the family Noctuidae. It is considered one of the most significant pests affecting cereal crops in sub-Saharan Africa.

Adult moths have a wingspan of approximately 30–40 mm. Their forewings display mottled brown and tan patterns, providing excellent camouflage against dead foliage and crop residue.

The larvae progress through several instars. Mature caterpillars are typically light brown to creamy-white, often with distinct pinkish stripes and a dark brown head capsule that aids in identification.

The life cycle is highly influenced by seasonal rainfall patterns. In favourable conditions, the species can complete two to three generations per year, leading to rapid population growth.

During the off-season or drought periods, the pest survives as mature larvae in diapause inside dry stalks of maize or sorghum, demonstrating high resilience to harsh environments.

The primary hosts of this pest include maize, sorghum, millet, and sugarcane. The larvae are specialized to feed on the interior tissues of these grass species.

Young larvae feed initially on the young leaves, causing characteristic window-pane perforations. As they grow, they bore into the central whorl and eventually the stalk.

Damage to the apical meristem or "growing point" leads to a condition known as "dead heart," where the central leaf withers and dies, effectively stunting the plant's growth.

Late-stage larval feeding involves extensive tunneling through the stalks. This disrupts nutrient uptake, weakens the stem, and makes the plant prone to lodging in windy conditions.

Furthermore, internal tunneling introduces pathogens and moisture, leading to internal rotting and secondary infections that significantly diminish grain quality and overall yield.

The emergence of the first generation of moths typically coincides with the arrival of the first rains of the season, which trigger the end of the larval diapause.

Females deposit eggs in small clusters underneath the leaf sheaths of young maize plants. These eggs hatch within a week, and larvae immediately begin looking for food sources.

Activity peaks during the mid-season when the crop is in its vegetative stage. During this time, the pest spreads rapidly if not monitored or managed correctly.

At the end of the harvest season, the population declines as larvae seek out remaining stalks to overwinter. This period is critical for destroying crop residues to break the cycle.

Continuous monitoring during the planting and vegetative growth phases is vital to prevent significant infestations from becoming uncontrollable later in the season.

The most recognizable early sign of an infestation is the presence of "shot-holes" or small transparent patches on the leaves, caused by early-instar larvae feeding.

The "dead heart" symptom is a classic indicator, characterized by the central leaf turning yellowish-brown and drying out while outer leaves remain relatively healthy for a time.

Frass (larval excrement) resembling fine sawdust is often found accumulating near the base of the leaves or around the entry points where the larvae have bored into the stalk.

Stunted plant growth and irregular stem development are common in fields where the stalk borer has been active throughout the early developmental stages of the crop.

• Window-pane lesions on young leaves.
• Dead central shoot (dead heart).
• Frass deposits on leaf axils.
• Exit holes on the surface of the stalk.

Agronomic practices, such as the destruction of crop residue immediately after harvest, are the first line of defense to prevent larvae from surviving until the next season.

Selecting and planting resistant or tolerant maize varieties remains the most cost-effective and environmentally friendly approach to long-term control.

Biological control, utilizing natural enemies like parasitic wasps and predatory insects, plays a crucial role in maintaining the pest population below economic damage thresholds.

Chemical control involving systemic insecticides is most effective when applied during the early whorl stage, before the larvae migrate deep into the stalks.

Integrated pest management (IPM) strategies, including crop rotation and the use of pheromone traps for monitoring, are essential for maintaining sustainable crop yields.