Potential impact of fall armyworm on sweet corn

Fall armyworm has a preference for maize, sweet corn, sorghum, rice and grass crops. Under high pest pressure, broadleaf vegetable crops can also be infested, and may be damaged.

Sweet corn is a preferred host of fall armyworm with a high risk of economic crop losses. Eggs are laid on the foliage of sweet corn plants and larvae feed on the leaves when they hatch. As the larvae grow, they consume more leaf area and feed deep in the whorl as well as in tassels and cobs.

Overseas, fall armyworm has rapidly developed pesticide resistance where subjected to repeated and prolonged use of insecticides.

What to look for

Fall armyworm can attack vegetative sweet corn at all growth stages, as well as feeding on the tassels and cobs. Later planted crops may be more severely affected.

Small larvae make 'windows' in leaves as they feed. Larvae feeding in whorls cause 'shot holes' in the unfurling leaves. The leaves of plants attacked by larger larvae will have a ragged appearance. Large larvae feeding in the whorl are often covered with a 'plug' of yellow-brown frass (caterpillar poo). If damage is evident, but larva is not visible, check the whorl to confirm identification as Helicoverpa armigera can cause similar damage in sweet corn crops.

How to manage an outbreak

Early detection is essential for effective control in sweet corn. Regularly check your crops for larvae and damage.

Seedling and vegetative crops can recover from some defoliation in early stages (V1–6), but plant growth may be affected by damage during the mid whorl stage (V6–V9). Damage during the late whorl stage (V9–R1) can subsequently result in significant losses in yield and cob damage.

Fall armyworm feeding at the whorl or tassel stage can then move into cobs during silking. A few days before tasselling, check whorls for larvae. These larvae can damage young cobs as they are pushed out of the whorl. Continue to check cobs for larvae until silks dry. Direct feeding damage to cobs, and frass contamination, will significantly impact yield and marketability of fresh cobs.

Large larvae in whorls under frass, and burrowed into cobs, will be largely protected from insecticide applications. For effective control, target small, leaf-feeding larvae.

Key to the control of any pest is an integrated pest management approach. With industry, we are working to identify strategies and tactics for the medium to long-term response. Of particular interest is the potential for the Trichogramma egg parasitoid to also parasitise fall armyworm eggs.

Some insecticides used for the control of Helicoverpa armigera, other armyworms and caterpillar pests may provide some level of control of fall armyworm. Biocontrol agents released for Helicoverpa are also expected to have an impact on fall armyworm.

Some products used for the control of Helicoverpa armigera, other armyworms and caterpillar pests may result in incidental control of fall armyworm.

Overseas, fall armyworm has rapidly developed pesticide resistance in frequently sprayed crops, including sweet corn. A resistance management strategy that considers both fall armyworm and Helicoverpa armigera is essential for the successful long-term management of these pests in sweet corn.

The Australian Pesticides and Veterinary Medicines Authority (APVMA) is currently assessing, as a priority, applications for permits for the use of chemicals against fall armyworm. Check for the latest chemical permits applying to fall armyworm by using the APVMAs permit portal—search for 'fall armyworm' and tick the 'pest/purpose' button.

You should already have strong on-farm biosecurity measures to protect your crops from pest and diseases and should implement good farm hygiene for weed control to remove hosts that could build populations.

Be on the lookout and if you suspect fall armyworm, report it immediately by phoning 13 25 23.

Further information

Read the sweet corn fall armyworm fact sheet.