The Menace of Stalk Borers: A Threat to Cereal Crops in Africa

Stalk borer, scientifically known as Busseola fusca, poses a significant threat to cereal crops, particularly maize, in Africa, with Kenya being heavily affected. This destructive insect belongs to the Noctuidae family, which includes other pests like cutworms and armyworms. The stalk borer larvae, as suggested by its name, tunnel into the stems of host plants and consume them from within. In this article, we will explore various aspects of stalk borers, including their host range, life cycle, identification, feeding habits, damage caused, survival strategies, and management techniques.

Host Range

Stalk borers primarily attack cereal crops, such as maize, sorghum, sugarcane, rice, finger millet, and thick-stemmed grass like Napier grass.

Life Cycle

The life cycle of stalk borers begins with the eggs, which are laid in a single column on the stems beneath the leaf sheaths. After approximately 10 days, the eggs hatch into larvae. These larvae go through six different instars. They migrate to the whorls of the plants and begin feeding. Usually, only one larva is found per stem due to their cannibalistic nature. The larvae mature in about 35 days and then pupate within the stem. The pupal stage lasts for about 2-3 weeks before the adults emerge.

Under favorable environmental conditions, the entire life cycle of stalk borers can be completed in 7-8 weeks.

Identification

Eggs: The eggs of stalk borers are spherical and light yellow. They possess around 70 radial ridges on their upper surface.

Larvae: Young larvae are generally dark brown or black and later turn creamish white with a gray or pink tint. Mature larvae measure about 40mm in length and have black spots along their bodies.

Pupae: Stalk borer pupae are approximately 25mm long, shiny, and range in color from yellow-brown to dark brown. Females are larger than males and can be found within the stem. They possess a plain pair of spines on their terminal cremaster.

Adults: The adult stalk borers are dark brown moths with patterned forewings and white to gray-brown hind wings. They have a wingspan of around 25-40mm. Females are larger than males and can lay up to 1000 eggs during their lifetime.

The larval stage of the stalk borer is the most destructive. Larvae have a biting and chewing feeding mode. They initially feed on the terminal leaf whorls, leaving behind a characteristic pattern of small holes. As the infestation progresses, they invade the growing points, resulting in dead hearts where the central leaves dry up and wither. Older larvae tunnel into the stems, weakening them and making them susceptible to breaking. Additionally, they tunnel into maize cobs, millet inflorescences, and sorghum peduncles, causing significant damage.

Severe damage occurs when the growing points of young plants are completely destroyed, stems are extensively bored, or the larvae feed on inflorescences and cobs. Infested plant parts also become more vulnerable to infections by other pathogens, such as fungi.

Yield losses attributed to stalk borers can reach up to 40%.

Survival Strategies

Stalk borers have the ability to overwinter, allowing them to survive for extended periods. In no-till fields, they reside in grass stems. During unfavorable conditions, the larval adults can hibernate at the base of the stems and emerge later. This adaptability enables the insect to withstand various climatic conditions. Furthermore, their wide host range provides a survival advantage to this pest.

Management Techniques

Considering the significant losses caused by stalk borer infestations, effective pest control measures are crucial to minimize damages. The most successful method of management involves using chemical insecticides. The following insecticides are highly recommended for eliminating stalk borers:

  • Kingcode Elite: Mix 10ml in 20l of water.
  • Lexus: Mix 8ml in 20l of water.
  • Pentagon: Mix 10ml in 20l of water.

Note

Always add 3ml of Integra to the insecticide mixture per 20l of water. This improves the efficacy of the product, acting as a sticker, spreader, and penetrant.

Other management techniques include:

1. Practicing crop protection by cultivating non-host plants.
2. Intercropping different crops to reduce the vulnerability of the main crop.
3. Maintaining field hygiene by removing crop residues and debris.
4. Implementing proper weed management practices to eliminate potential hiding places for the insects.

Conclusion

Stalk borers pose a significant threat to cereal crops in Africa, especially maize in Kenya. By understanding their life cycle, identifying their presence, and employing appropriate management techniques, farmers can effectively mitigate the damages caused by these destructive pests. Chemical insecticides, along with alternative practices like crop rotation and field cleanliness, play a crucial role in controlling and reducing stalk borer infestations, safeguarding crop yields and minimizing economic losses.

Add your comment