Helicoverpa armigera resistance management in grains

Author: | Date: 04 Dec 2018

Take home message

The H. armigera resistance management strategy in grains is designed to prolong the useful life of the newer chemistry currently available to pulse growers. Familiarise yourself with the strategy and the full range of options available for Helicoverpa control in chickpeas, mungbeans and soybeans. Consider what products you will use if a second spray is required in these crops.

The Helicoverpa armigera resistance management strategy (RMS)

This material has been extracted from the “Science behind the strategy” document. The RMS has been developed by the National Insecticide Resistance Management (NIRM) group, a part of the Grains Pest Advisory Committee (GPAC).

General rationale for the design of the strategy

Chickpeas and mungbeans are currently, and for the foreseeable future, the most valuable grains crops influenced by the RMS. Therefore, the RMS is primarily focused on insecticide Modes of Action (MoA) rotation in these systems and is built around product windows for Altacor® and Steward® because:

  1. Altacor® (chlorantraniliprole) is at risk from over-reliance in pulses, but resistance frequencies are currently low
  2. Steward® (indoxacarb) is at risk due to genetic predisposition (high level genetic dominance and metabolic mechanism) and pre-existing levels of resistance in NSW and QLD (with elevated levels in CQ during 2016-17). In addition, the use of indoxacarb in pulses is expected to increase as generic products come on to the market

In future, the RMS may include windows for other products e.g. Affirm® (emamectin benzoate), Success Neo® (spinetoram), and other new products that come to market, if their use patterns necessitate management.

There are two RMS regions, each with their own RMS designed to make the most effective products available when they are of greatest benefit, whilst minimising the risk of overuse:

  1. Northern Grains Region: Belyando, Callide Central Highlands & Dawson (Table 1)
  2. Central Grains Region: Balonne, Bourke, Burnett, Darling Downs, Gwydir, Lachlan, Macintyre, Macquarie & Namoi (Table 2)
  • The RMS provides windows-based recommendations common to Southern QLD, Central & Northern NSW because H. armigera moths are highly mobile and have the capacity to move between these regions, potentially increasing the risk of further exposing populations of H. armigera previously selected for resistance in other areas.
  • No RMS is currently proposed for the Southern and Western grain regions (Victoria, South Australia and Western Australia). Biological indicators are that the risk of H. armigera occurring in winter crops, at densities where control failures may occur, is presently considered low. Helicoverpa control in summer crops in these regions should use the Central Grains region RMS.

Use of broad-spectrum insecticides

The early use of synthetic pyrethroids (SPs) in winter pulses is a strategy adopted in southern Qld and northern NSW where the assumption is made that early infestations of Helicoverpa will be predominantly H. punctigera which are susceptible to SPs. Similarly, the use of carbamates to delay the application of Group 28 or Group 6 products, carries risks. If adopting this strategy, be aware of the following risks:

  1. Recent monitoring with pheromone traps has shown H. armigera to be present in all parts of the northern grains region from July-August (Beatsheet blog)
  2. Reduced efficacy of SPs and carbamates against H. armigera can be masked when treating very low population densities (< 3/sqm)
  3. If H. armigera are present, even at low levels in a population treated with SPs and carbamates, the treatment will select for further resistance. Whilst initial applications may be effective, later treatments may be significantly less effective

Table 1. Grains resistance management strategy for Helicoverpa armigera across Australia.
Best practice product windows and use restrictions to manage insecticide resistance in H.armigera.
Northern Region: Belyando, Central Highlands, Dawson and Callide.

Table shows Grains resistance management strategy for Helicoverpa armigera across Australia. Best practice product windows and use restrictions to manage insecticide resistance in H.armigera.  Northern Region: Belyando, Central Highlands, Dawson and Callide.

Table 1 - Notes:

  1. Some nC27 paraffinic spray oils can be used to suppress Helicoverpa populations and are best used as part of an IPM program.
  2. Observe withholding periods (WHP). Products in this group have WHP 14 days or longer.
  3. Maximum one spray of chlorantraniliprole alone or in mixtures per crop per season.
  4. Refer to label for warning of insecticide risk to bee populations.
  5. Maximum two consecutive sprays alone or in mixtures per crop per season.
  6. MODERATE RESISTANCE IS PRESENT IN H.ARMIGERA POPULATIONS – FIELD FAILURES LIKELY.
  7. HIGH RESISTANCE IS PRESENT IN H.ARMIGERA POPULATIONS – FIELD FAILURES EXPECTED!

Table 2. Grains resistance management strategy for Helicoverpa armigera across Australia. Best practice product windows and use restrictions to manage insecticide resistance in H.armigera. 
Southern QLD, Central & Northern NSW Regions: Balonne, Bourke, Burnett, Darling Downs, Gwydir, Lachlan, Macintyre, Macquarie & Namoi.

This table shows Grains resistance management strategy for Helicoverpa armigera across Australia. Best practice product windows and use restrictions to manage insecticide resistance in H.armigera.  Southern QLD, Central & Northern NSW Regions:  Balonne, Bourke, Burnett, Darling Downs, Gwydir, Lachlan, Macintyre, Macquarie & Namoi.

Table 2 - Notes:

  1. Some nC27 paraffinic spray oils can be used to suppress Helicoverpa populations and are best used as part of an IPM program.
  2. Observe withholding periods (WHP). Products in this group have WHP 14 days or longer.
  3. Maximum one spray of chlorantraniliprole alone or in mixtures per crop per season.
  4. Refer to label for warning of insecticide risk to bee populations.
  5. Maximum two consecutive sprays alone or in mixtures per crop per season.
  6. MODERATE RESISTANCE IS PRESENT IN H.ARMIGERA POPULATIONS – FIELD FAILURES LIKELY.
  7. HIGH RESISTANCE IS PRESENT IN H.ARMIGERA POPULATIONS – FIELD FAILURES EXPECTED!

Table 3. Explanatory notes for product windows in all regions.

InsecticideNumber of insecticide windowsDuration of insecticide windowsMaximum number of applications/crop/season
Chlorantraniliprole (Alcator®)210 weeks1
  • 10-week windows restrict selection to a maximum of 2 consecutive generations of H. armigera (includes 2–3 weeks residual beyond the end of each window i.e. 12–13 weeks total exposure).
  • Start date of first window correlates well with historical data relating to average daily temperatures that result in early pod-set.
  • Exposure of 2 consecutive generations is offset by long non-use periods (8 weeks in the central region and 18 weeks in the northern region).
  • Use is no recommended in spring mungbeans as there is less likelihood of both H. armigera and bean pod borer being present.
Indoxacarb (e.g. Steward®)Northern - 3
Central - 2
6 weeks1
  • 6-week windows restrict selection to a single generation of H. armigera.
  • Each window is followed by a non-use period of a minimum of 6 weeks.
  • Indoxacarb is an important early season rotation option for chickpeas and faba beans, and provides a robust selective alternative to Altacor® when Helicoverpa pressure is high.
Bacillus thuringiensis1Season longNo restrictions
No restrictions
2
Helicoverpa viruses
Spinetoram (e.g. Success Neo®)*
  • Low resistance risk and not widely used.
Emamectin benzoate (e.g. Affirm®)*1Season long2
  • Very low resistance frequency and not used widely.
  • However, emamectin benzoate is a good option for rotation to spread resistance risk away from Altacor®.
  • BUT industry needs to become more confident with using this product for it to be of value in resistance management.
Carbamates1Season long1
Synthetic pyrethroids
  • H. armigera resistance is present at moderate to high levels, but one strategic application per season in regions where H. punctigera predominates in early spring may be effective.
  • Carbamates are a rotation tool for indoxacarb and Altacor® either early season in chickpeas or late season in mungbeans.

*Resistance monitoring for selective products is a key component of the RMS and changes in resistance frequencies may result in the introduction of product windows for those insecticides not currently windowed.

Addressing questions on the RMS

The number of uses in the RMS is more restrictive than stated on the Steward® and Altacor® labels, why?

To avoid repeated use of either Steward® or Altacor® within the use window, the number of allowable applications is 1 per crop.  In some instances, the label registration may allow for more than one application; the recommendations were developed in consultation and supported by the chemical companies. It is anticipated that changes to product labels will follow to ensure consistency between labels and the RMS.

Does the RMS impact on recommendations for insecticide use in cotton and other grain crops?

The RMS is not intended to compromise the ability of the cotton industry to use any products registered for Helicoverpa in Bollgard®. This is because selection for insecticide resistance is considered low due to the high likelihood that survivors of conventional sprays used in Bollgard would be killed by Bt toxins expressed in plants. For further information go to: Cotton Info Pest Management Guide

Similarly, the RMS does not attempt to align the use of the Group 28s in mungbeans and chickpeas with use in other grain crops or horticulture. To do so would add a level of complexity that would make the RMS impractical.

Shouldn’t other MoAs be windowed to prevent the potential development of resistance to these products?

There is little evidence to suggest that other products should be windowed now to slow the development of future resistance. Both Affirm® (emamectin benzoate) and Success Neo® (spinetoram) show no sign of reduced susceptibility in testing (L. Bird, CRDC data). This result is consistent with the relatively limited use of these products in the grains industry to date. If a shift in susceptibility is detected in future testing, or the frequency with which they are used increases, it is the intention that the product/s will be windowed to limit selection pressure.

The SPs and carbamates are not windowed because there are already well established, relatively stable moderate-high levels of resistance to these MoAs and limiting their use will not change this situation.

By restricting the use of just the ‘at risk’ products, keeping the RMS as simple as possible, and allowing maximum choice of registered products, we anticipate that the grains industry will be more inclined (and able) to use the RMS.

The relative efficacy of the ‘softer’ options for Helicoverpa control in mungbeans and chickpeas – you aren’t totally reliant on Group 28s.

In 2017, QDAF Entomology undertook a number of trials to compare the knockdown/contact efficacy, and residual efficacy (persistence in the crop) of Altacor®, Steward®, Affirm® and Success Neo®. The purpose of these trials was to provide agronomists and growers with information on how well each of the products worked, and to provide confidence to use another option, rather than relying solely on the Group 28 products.

The results show that these products are equally effective on 3rd, 4th or 5th instar larvae that receive a lethal dose of the product – as would be achieved with good spray coverage (Figure 1a). But of course, there is considerable benefit in products persisting in the crop to control larvae that may hatch after the spray, or emerge from flowers, buds or pods where they may have been protected. The long residual efficacy of Steward® and now Altacor ® has been a major factor in their popularity. The data in Figure 1b shows the relative efficacy of these products from 0 – 20 days after treatment in the field (at 5-day intervals).

  1. For more information on the relative performance of these products in terms of feeding potential and recognising larvae affected by the different insecticides, see recent articles on the Beatsheet blog.

This column graph shows the relative efficacy (a) direct contact of softer options for Helicoverpa control in chickpea and mungbean crops.

This line graph shows the relative efficacy (b) residual, of softer options for Helicoverpa control in chickpea and mungbean crops.

Figure 1. Relative efficacy (a) direct contact and (b) residual, of softer options for Helicoverpa control
in chickpea and mungbean crops.

Another representation of the relative efficacy of the products is provided below (Figure 2) and shows how significantly the feeding (damage potential) of 3rd and 5th instar larvae was affected in the 24 hours post treatment with each insecticide. The graph clearly shows that feeding was significantly reduced in all treatments, compared with the controls. It also shows how much more feeding a 5th instar larva is capable of than a 3rd – emphasising the importance of controlling larvae before they are medium-large.

This column graph shows soybean leaf area consumed in 24 hours post treatment by 3rd and 5th instar Helicoverpa larvae. The leaf area consumed is representative of the relative damage potential of the larvae.

Figure 2. Soybean leaf area consumed in 24 hours post treatment by 3rd and 5th instar Helicoverpa larvae. The leaf area consumed is representative of the relative damage potential of the larvae.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, the author would like to thank them for their continued support.

Information on the H. armigera RMS is extracted from material prepared by NIRM to support the implementation of the RMS. The authors acknowledge the contribution of NIRM members to the development of this material.

We are grateful to the growers who allow us access to their farms and crops, and to the agronomists who assist us in locating potential field sites. We also thank the many growers and agronomists who share with us their experiences and insights into the issues they face and the practicalities of the management options we propose.

Adam Quade and Trevor Volp provided the technical expertise required to undertake the feeding trials.

NIRM (2018) Science behind the Resistance Management Strategy for Helicoverpa armigera in Australian grains.

Contact details

Melina Miles
Queensland Department of Agriculture and Fisheries
203 Tor St, Toowoomba. QLD 4350
Mb: 0407 113 306
Email: melina.miles@daf.qld.gov.au

® Registered trademark

GRDC code: DAQ00196, UQ00048 (NIRM)

GRDC Project code: DAQ00196, UM00048