Stalk borer (Busseola fusca) is the most important insect pest to most cereal crops e.g., maize in Africa, especially in Kenya. It belongs to the Noctuidae family of moths, which includes the cutworms and armyworms. As the name indicates, the larva of the stalk borer bores into the stalk/stem of the host plant and feeds within the plant.
Host Range
This pest attacks cereal crops. These include the following;
- Maize
- Sorghum
- Sugarcane
- Rice
- Finger millet
- Thick stemmed grass, e.g. Napier grass
Life Cycle
Eggs are laid in a single column on the stem under the leaf sheaths and hatch after about 10 days into larvae. There are 6 larval instars. These instars migrate to the whorls and begin feeding. Usually, only one larva is found per stem because they are cannibalistic. Larvae mature in about 35 days after, then pupate in the stem. The pupae live for about 2-3weeks and turn to adults.
In a conducive environmental, the life cycle of this insect can take 7-8weeks.
Identification
- Eggs– are spherical and light yellow in colour. They are characterized by about 70 radial ridges on their upper surface.
- Larvae– the young larvae are usually dark brown or black in colour. Later, they turn creamish white with a gray or pink tint. A mature larva is about 40mm long and has black spots along the body.
- Pupae-these are about 25mm long and shiny yellow brown to dark brown in colour. Usually, the females are bigger than the males, are found within the stem and have a plain pair of plain spines on their terminal cremaster.
- Adults– they are dark brown, with patterned forewings and white to gray brown hind wings. They have a wing span of approximately 25-40mm. The females are bigger than the males and can lay up to 1000 eggs in a lifetime.
Feeding and Damage
The most destructive stage of the insect is the larval stage. Larvae have a biting and chewing mode of feeding. They feed on the terminal leaf whorls leading to production of a characteristic pattern of small holes. As infestation progresses, they invade the growing points causing dead hearts, whereby the central leaves dry and wither. The older larvae tunnel in the stem. As they feed, they weaken the stem causing it to break. They also tunnel into maize cobs, millet inflorescences and sorghum peduncles leading to significant damages.
Damage is very critical when the growing points of young plants are damaged completely, when stems have been bored extensively and when the larvae feed on the inflorescences, cobs, etc.
Infested parts facilitate infection by other pathogens like fungi.
Yield losses attributed to stalk borers areas high as about 40%.
Survival
A stalk borer has the capability to over winter and can thus live for relatively longer periods. In no till fields, they stay in grass stems. The adult larva can hibernate at the base of the stem during unfavourable conditions and emerge later. This insect can thus survive varied climatic conditions. The wide host range also gives a survival advantage to this insect pest.
Management
Infestations by stalk borers causes significant losses. It is therefore of great importance to control this pest in order to avoid these losses.
Various ways can be employed in the management and control of this insect pest. However, the most effective method is the use of chemicals (insecticides).
Therefore, to get rid of stalk borers, the following insecticides are highly recommended;
- Kingcode Elite 10ml/20l
- Lexus 8ml/20l
- Pentagon 10ml/20l
NB; Always mix the insecticide with Integra 3ml/20l whenever spraying. This improves the efficacy of the product. It is a sticker, spreader and penetrant.
Other methods include
- Practicing crop protection with non-host plants
- Intercropping
- Maintaining field hygiene
- Proper weed management in order to ensure the insect cannot hide in the weeds
