The basics of cutworm management

While the presence of weeds strongly influences the pest status of cutworm, the influence of soil moisture on factors such as their biology and behaviour are often overlooked. Entomologist and Bt-maize expert Prof Johnnie van den Berg and Zunel van Eeden, a master's student at North-West University's Integrated Pest Management group, have undertaken research on cutworm behaviour, control and insecticide resistance.

- Johnnie van den Berg and Zunel van Eeden

The common cutworm, Agrotis segetum (Lepidoptera: Noctuidae) is a destructive pest of maize, especially in the Highveld region of South Africa. Over the three previous cropping seasons, many reports of control failure have been made throughout the region. Although there is speculation regarding insect resistance to insecticides, the observed control failures are most likely due to other factors, such as larval behaviour and environmental conditions, and, notably the presence of weeds.

WHY IS IT DIFFICULT TO IDENTIFY CUTWORM?

Identification of cutworm as the pest responsible for injury to seedlings in a particular land is difficult due to their habit of tunnelling into the soil during the day and feeding at night. It is therefore difficult to detect larvae to associate with the observed damage symptoms, which could possibly also be due to other soil insect pests. When damaged or dead seedlings are observed, the soil around the base of the plants should be examined for the presence of cutworms. Larvae can be observed beneath clods, inside their tunnels, or in soil cracks.

SIGNS OF CUTWORM INFESTATION

Cutworm damage is influenced by the quantity and size of larvae present in lands. Only if seedlings are seriously damaged and when stand loss occurs, can damage be considered economically important. Damage symptoms to maize seedlings can be grouped into five categories, depending on the size of the larvae and the age of the plant.

Stand loss