Farmers urged to scout for maize stem borers

The African maize stem borer ( Busseola fusca) is one of the most severe maize pests in Africa. In an effort to mitigate the impact of the pest, Grain SA (GSA) has called on local maize producers to collect representative larval populations for research purposes.

GSA said in a statement that this was important to screen future maize varieties for resistance to the African maize stem borer in order to protect maize crops against it.

This stem borer was indigenous to sub-Saharan Africa, with maize and sorghum being its main crop hosts. In the larval stage, the caterpillars fed on young leaves from where they entered the stems, severely damaging the plants. In older plants, stem borer feeding could result in markedly reduced grain yields, the statement said.

According to Elrine Strydom, junior researcher at the Agricultural Research Council’s (ARC) Grain Crops Institute in Potchefstroom, in Africa maize fell prey to many Lepidopteran pests.

In South Africa, producers also had to contend with the spotted stem borer ( Chilo partellus) and the pink stem borer ( Sesamia calamistis), in addition to B. fusca.

The African maize stem borer presented three distinctive “moth flights” per season. Strydom said plants were infested by either the first or second stem borer generation, depending on planting dates. Female moths laid their egg parcels behind the leaf sheaths of the plants. After hatching, the larvae migrated to the whorl leaves to feed, before burrowing into the stem. Larger larvae fed through the rolled whorl leaves, leaving visible rows of holes as leaves matured.

As much as 10% of the South African maize yield was lost to stem borers annually, according to Strydom. In extremely severe cases, 100% yield losses were reported in individual farming operations despite chemical control measures.

“All three of these maize stem borer species are successfully controlled by Bt maize. Bt transgenic maize can therefore alleviate the stem borer infestation problem to a large extent. However, the African maize stem borer has developed a resistance to first-generation Bt maize. This is of major concern, and that is why continuous monitoring is so important,” she said.

GSA requested maize producers who spotted stem borer damage and had collected larvae to contact the Grain Research Programme team at the University of Pretoria by emailing PfanoMbedzi@ fabi.up.ac.za. Alternatively, they could download the Biosecurity Africa app for free at cropwatch. africa/ biosecurityafricaapps/.