Research has shown that an interaction between the ear rot fungi, Fusarium verticillioides, and stalk borer, Busseola fusca, can lead to an increased incidence of fusarium ear rot in maize.

HOW TO REDUCE DAMAGE

Several practices could be followed to reduce B. fusca and F. verticillioides interactions.

These include:
The use of genetically modified hybrids
The planting of Bt maize hybrids has become an important tool for the integrated management of stem borers and diseases of maize. Farmers prefer Bt maize hybrids for their convenience and yield protection, reduced need for chemical insecticides and improved grain quality.

Some farmers, however, still rely on traditional pest management methods to control maize pests. These farmers often have to weigh up the advantages of buying stalk borer protection “in the bag” against other possible economic and environmental management issues.

Push-pull habitat manipulation
A habitat management strategy, based on a stimulo-deterrent or “push-pull” approach has been developed for cereal stem borer management in eastern Africa. In this system, trap plants such as Napier and Sudan grass emit chemical compounds that attract invading adult moths to lay eggs on them, thereby reducing infestation pressure on maize plants.

These grasses are planted along the border around maize fields. The trap plants provide the “pull” in the system that also serves as a refuge for the stem borer’s natural predators. The “push” is provided by plants such as Desmodium spp., which emit chemicals that repel stem borers from maize in an intercropping system.

Leguminous Desmodium intortum is planted between maize rows. These plants also provide soil nutrient stability through nitrogen fixing and are a highly nutritious fodder crop. It is drought-tolerant.

Also read: Companion “push-pull” crop system proves successful against fall armyworm in East Africa

Sound cultural practices
Crop residues provide a habitat for stalk borer larvae populations between seasons. Stalk borer densities can be reduced by managing crop residues – for instance, by removing stover and ploughing in stubble.

Adapting planting dates
To avoid distinct periods of moth flights by planting short growing-season maize varieties could mean that damage is avoided and yield losses reduced. Stalk borer larvae tend to migrate to neighbouring plants, so plant density has a significant effect on the extent of maize yield losses to this insect pest.

Fusarium verticillioides colonisation can also be reduced through production practices such as planting hybrids adapted to local climatic conditions, using hybrids having tight husks, avoiding excessive plant populations, maintaining adequate levels of nitrogen and other essential growth nutrients, sub-soiling in compacted soils to minimise plant stress and reduce disease inoculum levels.

THE USE OF PESTICIDES

Because of the economic and social constraints farmers in Africa face, pesticide use on the continent is among the lowest in the world. Stalk borer larvae primarily feed in the whorls of plants until the fourth stage of their development, so applying insecticides in the whorls is effective until shortly before tasselling.

Insecticide applications are often ineffective, however, because active substances cannot reach deep enough inside the stems where the stalk borers reside.

QUICK FACTS

• Larvae of the maize stalk borer, Busseola fusca, often interact with fusarium fungi, resulting in increased occurrence of rotten maize grain.
• Fusarium verticillioides is best known for causing maize ear rot, but symptoms can vary from non-symptomatic infections to severe rotting of roots, stems and ears.
• The most detrimental effect of F. verticillioides is that it produces fumonisin mycotoxins that have been associated with diseases in humans and livestock.

Also read: Mycotoxins in grains in subsistence farming systems: A threat to food safety and food security

• This article was written by Edson Ncube and Prof. Johnnie van den Berg and first appeared in Farming SA.