A new resistance management strategy (RMS) for Helicoverpa armigera has been released for the northern grain production region. It is anticipated that it will be adopted first in the current chickpea crop.
H. armigera is a major pest of grain crops and presents a significant management challenge due to the current reliance on chemical control, and resistance to several insecticide groups. Whilst H. armigera has been recorded in all states and territories of Australia, it is most frequently a pest in the northern and coastal regions of eastern Australia so the strategy is focussed on these regions. Within these regions, it is the grains industry, particularly summer and winter pulse production (principally chickpea and mungbeans), where the greatest selection pressure is exerted on H. armigera. The cotton industry, now dominated by Bt varieties, makes a relatively small contribution to the overall selection for resistance to conventional insecticides.
The focus of the strategy is to slow the rate at which resistance develops to those insecticides that are currently very effective, and on which the grains industry is highly reliant.
While the majority of the more than 200 registered products for H. armigera control fall within three broad-spectrum categories (carbamates (1A), organophosphates (1B), and synthetic pyrethroids (1C)), some of the more selective insecticide groups have become popular in pulses due to their high efficacy and low impact on benefical insects. Two of these in particular are considered at ‘high risk’ of developing resistance—chlorantraniliprole (28) because of high levels of reliance on it in pulse crops, and indoxacarb (22A) due to pre-existing resistance levels in some areas and a the expectation usage will increase. Therefore, the RMS has been primarily built around product windows for these two insecticide groups, but includes consideration of the relative selectivity or ‘softness’ of the pesticide group used.
Things to consider when referring to this RMS:
- The Southern and Western Grains regions (Victoria, South Australia and Western Australia) are not included as there is limited knowledge of the occurrence risk of H. armigera in winter crops in these regions, but it is considered low.
- Northern and Central RMS regions (represented by Tables 1 and 2) have different windows because of differences in cropping seasons due to climate.
- The RMS Table 2 groups the areas of southern Queensland to the Namoi together because H. armigera moths are highly mobile and have the capacity to move between these areas, potentially increasing the risk of further exposing cohorts of insects previously selected for resistance.
- IPM tactics such as minimising pest build up on weeds, pupae busting, use of economic thresholds, selection of soft options, and effective monitoring are integral to achieving a reduction in overall pesticide use, and thus helping to minimise the resistance risk.
General principles to avoid or minimise resistance development:
- Avoid repeated use of insecticides from the same chemical group
- Comply with all directions on product labels – DO NOT cut rates or exceed the recommended applications per crop per season
- If a spray fails due to resistance or unknown cause, do not re-spray in the same season using a product from the same chemical group
- Where possible, use target-specific ‘soft’ chemicals rather than broad-spectrum pesticides
- Correctly identify the pest to ensure the most effective insecticide and rate is use.
- Monitor beneficial populations to determine if chemical control of helicoverpa is warranted
- Consider the impact on all species present when applying insecticide sprays
- Ensure spray rigs are calibrated properly and sprays achieve good coverage
- Monitor post-treatment for evidence of loss of field efficacy and report field failures.
Read the full RMS and explanatory documentation at IPM Guidelines for grains.
The Helicoverpa RMS will be one of the topics for discussion at the upcoming GRDC Updates in Narromine (23 July), Gunnedah (24 July), North Star (25 July) and Pittsworth (26 July).