Fall armyworm insecticide resistance surveillance

Since 2022 an insecticide resistance surveillance program for fall armyworm has been conducted annually by NSWDPIRD in collaboration with QDAF entomologists. The program is focused on resistance testing in fall armyworm populations collected from major cropping regions of northern, central and southern Queensland and is aimed at keeping growers and crop managers informed about potential fall armyworm resistance outbreaks in the northern region.

The program utilises F₂ screening for detecting resistance to key selective insecticides registered for fall armyworm control including indoxacarb, emamectin benzoate, spinetoram and chlorantraniliprole which now have broad registration in grains and horticultural crops.

The predictive capability of the F₂ screening means that industries can implement management tactics for reducing economic losses before spray failures occur, as well as minimising further spread of resistance genes throughout the wider fall armyworm population and potential resistance selection in other important lepidopteran pests in the northern regions such as Helicoverpa armigera (cotton bollworm / corn earworm) and Spodoptera litura (cluster caterpillar).

Overall summary of results from 2022-24:

• Chlorantraniliprole (e.g., Vantacor®) – No resistance
• Emamectin benzoate (e.g., Affirm®, Warlock®) – No resistance
• Spinetoram (e.g., Success Neo®) – No resistance
• Indoxacarb (e.g., Steward®) – No change in resistance from baseline levels

 Regional results of fall armyworm resistance testing 2022-24:

Each active is provided in a separate table (n = number of alleles tested).

Implications for fall armyworm management

Testing data from the past two seasons indicated that alleles for resistance to chlorantraniliprole, emamectin benzoate, spinetoram and indoxacarb are still extremely rare in Queensland fall armyworm populations and this is a positive sign that these insecticides will continue to provide effective control of fall armyworm in the coming season.

Patterns of variability in different seasons and in different regions are likely to reflect localised insecticide usage patterns. Increased spraying for fall armyworm may have also increased selection pressure in maize, sweetcorn and sorghum where H. armigera is also a pest.

However, it will be important for crop managers to mindful of the potential for fall armyworm to develop resistance due to the high rates of insecticide use for control fall armyworm across a range of cropping systems.

To reduce the risk of lost productivity due to resistance, growers are urged to comply with key recommendations to minimise selection pressure on chemical mode-of-action group across consecutive generations of fall armyworm.

Using a broad range of IPM options to specifically target fall armyworm and promote natural enemies in crops will reduce over-reliance on any one chemical group.  Following these recommendations and complying with label instructions will minimise the risk of spray failures and support sustainable management of fall armyworm.

 General principles to minimise resistance development:

• Comply with all directions on product labels – DO NOT cut rates or exceed the recommended applications per crop per season.
• Avoid repeated use of insecticides from the same chemical group; if a spray fails due to resistance or unknown cause, do not re-spray with that group again in the same season.
• Monitor regularly, using appropriate sampling techniques.
• Correctly identify the pest to ensure the most effective insecticide and rate is used.
• Monitor beneficial populations to determine if chemical control of the pest is warranted.
• Use economic thresholds, if available, when making spray decisions.
• Avoid prophylactic sprays.
• Use target-specific ‘soft’ chemicals where possible, rather than broad-spectrum pesticides.
• Consider the impact on all species present when applying insecticide sprays; be aware of potential implications for Helicoverpa resistance when managing for fall armyworm.
• Ensure spray rigs are calibrated properly and sprays achieve effective coverage.
• Monitor post-treatment for evidence of loss of field efficacy and report field failures.

Further information:

• Download a copy of the Helicoverpa RMS and the about the science behind it.
• Learn more about insecticide resistance
• Latest surveillance information for helicoverpa

This research has been supported by GRDC in project DPI2307-002RTX ‘Resistance surveillance for sustainable management of helicoverpa and fall armyworm in grains’.