Pulse Australia

Photo: Hugh Brier, DAF

Diligence needed to manage Helicoverpa resistance in mungbean

The information in this post relates specifically to mungbean. However, helicoverpa are also a problem in soybean and peanut crops in coastal environments. Hugh Brier (DAF) and Andrew McDonald advise that growers should follow this resistance management strategy in soybean and peanut crops also.

To combat the threat of resistance development, the following recommendations are made for agronomist and growers to implement:

• No more than one application of Steward, Altacor, carbamates and synthetic pyrethroids per crop either alone, or in mixtures (label currently allows for two applications).
• No more than two applications of Affirm or Success Neo per crop, alone or in mixtures.
• Rotate use of Steward, Altacor, Affirm and Success Neo within the season.
• Avoid the use of Steward as the last spray in the crop, particularly if applied to a population of Helicoverpa that will go into winter diapause (i.e after mid-March).
• No restrictions applies to Bacillus thuringiensis (Bt), Helicoverpa viruses and Paraffinic oil.
• Have a strategy ready to deal with early infestations and with multiple pests.

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Source: Australian Mungbean Assoc

Not only is Helicoverpa of significant economic importance for mungbean yield and quality, the introduced species, Helicoverpa armigera, is particularly adept at developing resistance to insecticides.

Having already developed a significant level of resistance to broad spectrum insecticides such as organophosphates, carbamates and pyrethroids, entomologists are strongly recommending that growers make every effort to prolong the effective life of the newly-registered insecticides for use in mungbean.

Dr Lisa Bird (NSW DPI), lead researcher for the Helicoverpa Insecticide Resistance Program, is very concerned that resistance levels to indoxacarb (Steward) are increasing across the geographic range of H. armigera. She says there has been more than a 2-fold increase in resistance to Steward recorded in just one year, to an average 6 per cent of the population in 2016–17, and as high as 9 per cent in Central Queensland, where H. armigera are able to survive all year-round.

“Chlorantraniliprole (Altacor) is another newly-registered product in mungbeans where we are seeing early evidence of Helicoverpa evolving resistance,” she says. “Altacor has proven to be a very useful product, providing excellent knockdown on Helicoverpa, and other important caterpillar pests, as well as providing a significant residual effect and being relatively ‘soft’ on beneficial species. While resistance levels are still below 1 per cent, there is a detectable level of resistance at many monitoring sites and the resistance genes are at risk of spreading across the growing regions.”

Mungbeans and chickpeas are the most widely grown crops that have a heavy reliance on Group 28 insecticides, including Altacor. Dr Bird says that while resistance frequencies are currently low, an over-reliance on this very effective product will increase frequencies and consequently result in a loss of efficacy.

“H. armigera have a genetic disposition to resist Group 22 insecticides such as Steward,” she says. “With already elevated levels of resistance evident in NSW and Queensland, along with the fact that Steward is now off-patent in Australia, allowing lower priced products to enter the market, there is potential for increased selection pressure if the use of these products is not managed carefully.”

“Helicoverpa moths are highly mobile, with the capacity to move between regions. This mobility potentially increases the risk of further exposing populations of Helicoverpa previously selected for resistance,” says Dr Bird. “Adherence to the resistance management recommendations is particularly relevant in regions where both chickpea and mungbeans are grown. These recommendations do not apply to cotton crops where survivors of conventional sprays used in Bollgard crops would be killed by BT toxins expressed in the cotton plants.”

To avoid unnecessary, or prophylactic, sprays it is essential that growers and their agronomists are frequently monitoring crops and applying sprays in a timely manner to maximise the number of viable flowers and undamaged pods.

There are two new registrations now available to growers – emamectin benzoate (Affirm, Group 6) and spinetoram (Success Neo, Group 5), both of which are comparable to Steward in activity. Rotating between these four products, and using other insect control measures such as products containing Nuclear Polyhedrosis Virus (NVP), will spread resistance risk across all mode of action (MoA) groups and extend the effective life of all four pesticides.

All four are ingestion products, so good coverage is essential. For best results, follow the manufacturer’s ‘critical application parameters’, including water volumes over 100 L/ha, medium droplet size and vehicle speed below 20 km/hr. And consider using higher water volumes and a different nozzle setup if the crop is particularly large or dense.

These four insecticides are also registered for use in a number of other crops and for other insect pests. This potentially increases the number of applications throughout both summer and winter and increases the level of secondary exposure in Helicoverpa, both of which can heighted selection pressure for resistance.”

Hugh Brier, Department of Agriculture and Fisheries, Queensland entomologist at Kingaroy reminds growers and agronomists to use threshold calculations to ensure sprays are only applied when it is economic to do so and to maximise beneficials to control survivors, further reducing the risk of resistance developing.

Where Helicoverpa causes defoliation prior to budding, and control is deemed necessary, Mr Brier suggests growers consider trialling NPV for moderate Helicoverpa populations (< 6/m2). Given the short duration of mungbean crops, two sprays for Helicoverpa should be considered a maximum and, in most crops, one spray suffices. Application of NPV early in the season will assist the strategic use of other options to control Helicoverpa later in the season.

“One-well-timed treatment can effectively control both Helicoverpa and podborer. Otherwise, podborer infestations can be effectively controlled with either Altacor or Steward while Affirm is an effective alternative to Altacor and Steward for control of Helicoverpa in mungbeans,” he says. “In the event of sustained Helicoverpa pressure, growers need to consider how they can rotate Altacor, Steward, Affirm, carbamates and NPV.”

• Beatsheet Blog – New strategy released to manage helicoverpa resistance

• Podcast with Melina Miles
• Resistance management strategy
• Science behind the strategy

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