Potential impact of fall armyworm on sorghum
Sorghum is a host of fall armyworm. It is at risk of damage at the vegetative stage and at risk of significant yield loss with infestations at grain-filling stages.
In the United States of America, fall armyworm is considered to be as damaging as helicoverpa in sorghum at grain-filling stages.
Crops at greatest risk of fall armyworm infestation, from local population build up or migration, are likely to be:
- autumn-sown crops in Central Queensland
- late sown crops through the southern parts of Queensland.
Overseas, fall armyworm has rapidly developed pesticide resistance where subjected to repeated and prolonged use of insecticides.
What to look for
Monitor for fall armyworm in sorghum just as you would for Helicoverpa armigera, paying particular attention to defoliation in the establishment and vegetative stages. Fall armyworm can damage younger sorghum plants, but this does not usually impact plant growth and yield, unless pest pressure is high and defoliation severe. Look for damage on the lower leaves and the whorl.
Fall armyworm larvae typically infest the whorl of sorghum plants, causing large, irregular-shaped holes in emerging leaves. Helicoverpa armigera and other armyworm species will cause similar damage in sorghum, so it is important to open up the whorl to identify the larvae.
How to manage an outbreak
Early detection is essential. Regularly check your crops for insects and damage.
An integrated pest management approach is the key to the control of any pest. We are working with industry to identify strategies and tactics for the medium to long-term response.
Like Helicoverpa armigera, small fall armyworm larvae feed on the pollen and larger larvae feed on the developing grain. Managing infestations before heads emerge will reduce the risk of this type of damage.
In the event of infestations during the vegetative stage of growth, the United States of America control guidelines recommend intervention if damage results in more than 30% defoliation, or there are 1–2 (or more) larvae per whorl. If the infestation occurs during the grain fill stage, use the Helicoverpa economic threshold calculator at The Beatsheet.
Some insecticides used for the control of Helicoverpa armigera, other armyworms and caterpillar pests may provide some level of control of fall armyworm. Be aware that insecticides applied for fall armyworm control will incidentally expose Helicoverpa armigera in the crop, and increase selection pressure for resistance.
For any pesticide use for fall armyworm control, you must consider the implications for chemical resistance development in other pests that may be exposed (e.g. Helicoperva) and the potential impact on natural enemies.
The APVMA is currently assessing, as a priority, permit applications for the use of additional insecticides for 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' option.
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.
Read the sorghum fall armyworm fact sheet.