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Potential impact of fall armyworm on maize crops

Corn or maize is a preferred host of fall armyworm with a high risk of significant crop losses.

Eggs are laid on the foliage of maize plants and larvae feed on the leaves when they hatch. As the larvae grow, they consume more leaf area and large larvae will establish themselves in the whorl.

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

What to look for

Look for egg masses and small larvae. Larvae may be more active at night. Watch for defoliation of lower leaves, shot holes in new leaves as they unfurl, and other leaf damage, loss of tassels or damage to cobs.

Where heavy infestations occur, frass (insect poo) will be visible on leaves and in the whorl. If damage is evident, but larvae are not visible, thoroughly check the whorl as larvae and moths will shelter in the whorl during the day.

Fall armyworm larvae can attack maize at all growth stages. The damage to leaves, the whorl and cobs, is similar to damage caused by Helicoverpa armigera and common armyworm.

Seedling and vegetative crops can recover from defoliation, particularly if the crop is growing rapidly. Larvae can sever seedling maize plants at the base, producing damage similar to that caused by cutworm.

Impact on yield will be greatest if the growing point is damaged or if there is significant defoliation at critical growth stages (around 10 days prior to and 20 days after tasselling/flowering). Feeding damage to cobs during grain filling will also impact on yield and grain quality.

How to manage an outbreak

Early detection is essential. Regularly check your crops for insects and damage.

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.

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.

There are currently no locally derived thresholds to guide management of fall armyworm due to lack of time to assess the impact on maize in Australia.

Guidance from the United States of America recommends to check 20 consecutive plants in a row and count the number of larvae per plant. Make sure to open the whorl/cobs in older plants. Repeat at 5 sites in the field. The threshold for control is reached when 3 or more larvae are found per plant, or 20% of whorl stage plants have 1 or more larvae. In making this assessment, it is essential that a positive identification of fall armyworm larvae is established.

It is essential with any pesticide use for fall armyworm control, that the implications for chemical resistance development in other pests that may be exposed are considered (e.g. Helicoverpa), as well as the potential impact on natural enemies.

The APVMA is currently assessing, as a priority, applications for permits for the use of a suite of chemicals against fall armyworm in crops. 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 maize fall armyworm fact sheet.