Maize stem borer (Sorghum)

Authors: J. van den Berg, A. Erasmus, M. van Rooyen. Text extracted with permission from the editors from: Prinsloo, G.L. & Uys, V.M (Eds) 2015.  Insects of Cultivated Plants and Natural Pastures in Southern Africa.  Entomological Society of Southern Africa. Buy the book.
Maize stem borer, Busseola fusca. Larval damage to a maize ear. - A. Erasmus, ARC
Maize stem borer, Busseola fusca. Larval damage to a maize ear. - A. Erasmus, ARC

Busseola fusca

Other common names: maize stalk borer, African stalk borer; mieliestamrusper (A); broca-do-colmo (P)

Damage

Whorl damage is characteristic of stem borer larvae that spend the first 10-14 days in the whorls of plants. When infestation takes place at early plant growth stages, plants may develop dead heart symptoms. Dead heart occurs when the growth point is killed by larval feeding and results in the wilting and drying of whorl leaves. When infestation occurs at later growth stages, especially during the flag leaf and boot stages, larvae damage the peduncle of the panicle, which leads to peduncle breakage and possible loss of panicles during heavy rains or during harvesting process.

The maize stem borer is a chronic pest of sorghum that may cause serious damage if it is not controlled. At high elevations it is of greater importance than the chilo borer, which is the predominant borer species in low lying and subtropical areas. These two species often occur in mixed populations on sorghum on the Highveld region in South Africa.

Management

Chemical control by means of insecticidal sprays is effective against stem borer larvae when they are still in the whorls of plants. An action threshold value of the 10% damaged plants per fields is used as guideline in determining when insecticides should be applied. Only when this infestation level is reached, are insecticide applications warranted. Since borer larvae spend at least 10-14 days inside the whorls of plants, they are relatively easily reached by insecticides. Whorl application is therefore the most effective method of control when insecticides are used.

If the action threshold principle is not applied due to fields being too large or scouting constraints, applications can be done on the basis of the plant growth stages. The broad principles that apply when mixed stem borer populations are present are as follows: in the case of the early plantings, insecticide application should be planned to coincide with late plant growth stages of the crop; in late planting, an early insecticide application will be needed, with the possibility of a follow-up application during the flag leaf stage.