The cutworm scourge, and how to control it

The dominant cutworm, Agrotis segetum, is causing renewed, costly damage to South African maize, soya bean, and sunflower.

- Zunel van Eeden reports.

Agrotis segetum is the dominant cutworm species and the most important pest of maize seedlings in South Africa. Historical literature from Drinkwater et al (1992) recognises A. segetum as the only Agrotis species of economic importance in the country.

Recent surveys conducted by Van Eeden et al (2025) confirm that over the past four planting seasons, producers have reported a renewed increase in the pest status of this species, accompanied by severe seedling losses in maize and, for the first time, verified stand losses in soya bean and sunflower. Across the 150 363ha surveyed, the economic impact of cutworm damage amounted to R44,87 million, emphasising the current relevance of this pest in grain production systems.

Understanding the biology of A. segetum, its association with winter weeds, and the influence of cultivation practices, such as tillage, on the pest, is essential for interpreting why infestations occur.

BIOLOGY AND SEASONAL ECOLOGY

Cutworms are polyphagous pests of numerous crops including maize, soya bean, sunflower and a range of other host plants. In South Africa, A. segetum survives the autumn and winter months as larvae of varying instars, surviving on winter weeds and hiding beneath plant residues or within the soil. Eggs are laid on the soil surface, weeds or crop residues after harvest. This period is critical for population build-up leading into the spring planting season.

The availability of winter weeds exerts a strong influence on larval survival, abundance and subsequent damage potential.

EARLIER STUDIES HAVE SHOWN THAT CUTWORM LARVAE REMAIN CLOSELY ASSOCIATED WITH WINTER WEEDS AND VOLUNTEER MAIZE THROUGHOUT WINTER