Stem Borers

Adults are usually small, drab moths that fly at night and are rarely noticed; identification in the field relies mainly on larval damage and, where needed, on rearing or expert confirmation of the caterpillar. Larvae are cylindrical, cream to pinkish, sometimes with faint longitudinal stripes, and are found inside hollowed stem tissue.

Early symptoms include small pinholes in leaves from young larvae feeding before boring in, followed by a wilted, dead central shoot known as "deadheart" in vegetative-stage cereals, or a dried, empty "whitehead" panicle if boring occurs after heading.

Moths lay egg masses on leaves or stems, and newly hatched larvae feed briefly on leaf tissue before boring into the stem, where they tunnel and feed for several weeks. Depending on species and climate, there may be several overlapping generations per season.

Many species survive between cropping seasons as larvae or pupae inside crop residue or stubble, which is why residue management is a recurring theme in cultural control.

Tunnelling disrupts the movement of water and nutrients within the stem, killing the growing point in young plants and weakening stems in older ones, which can lead to lodging and reduced grain fill. Damage severity depends on plant growth stage at attack, borer density, and variety.

Host crops include maize, rice, sorghum, and sugarcane, with the mix of species involved varying substantially by region.

Field scouting for egg masses, pinhole leaf feeding, and early deadheart symptoms helps identify infestations while larvae are still exposed and before they bore into stems. Pheromone traps are available for some species to track adult moth activity and time scouting.

Because larvae become protected once inside the stem, stem borer management emphasises prevention and early-stage tactics within an integrated approach.

• Destroy or incorporate crop residue and stubble that can harbour overwintering larvae
• Use resistant or tolerant varieties where available
• Conserve parasitoid wasps and flies and other natural enemies
• Scout regularly and time any intervention to the vulnerable young-larval stage