Jointly funded GRDC and Cotton Research and Development Corporation (CRDC) survellience has found that resistance of Helicoverpa to synthetic pyrethroid insecticides suddenly spiked last year, posing a challenge to chickpea producers this spring.
Dr Lisa Bird, a research officer from New South Wales Department of Primary Industries, observed that resistance to bifenthrid (Talstar®) was approximately 10 per cent between 2009 and 2011, while general synthetic pyrethroid resistance (measured by the insecticide fenvalerate) was about 60 per cent.
“In 2011-12 there was a 30 per cent increase in resistance in H. armigera. Average resistance to bifenthrin is now 40 per cent, while general resistance has increased from 60 per cent to 90 per cent.”
With such high levels of resistance, Tracey Leven from the Cotton Research and Development Corporation (CRDC) says; “We are alerting people through cotton’s resistance management strategy to the fact that the resistance levels are so high now, people should expect field failures with these products.”
“It doesn’t matter which pyrethroid you use, the population is resistant to all of them,” Dr Bird says.
Helicoverpa armigera (formerly known as Heliothis grubs) are a significant pest of a wide range of crops, including cotton, chickpeas and faba beans. “This species has repeatedly demonstrated a great capacity for developing resistance to synthetic insecticidal chemistries,” Dr Bird says.
The increase in resistance is consistent across the cotton-growing regions. Monitoring takes place from southern NSW to central Queensland. “In order to minimise resistance risk and ensure the sustainability of insecticidal products, it is important for growers to consider the longer-term cross-industry implications of spray decisions for Helicoverpa control,” she says.
The sudden jump comes after a period of low-resistance as the cotton industry adopted transgenic cotton and insecticide management strategies.
Ms Leven explains that although Helicoverpa is the main insect pest in cotton, it no longer causes economic damage, thanks to GM cotton. Adoption of GM cotton is very high, at about 98 per cent. Since 2005-06 less than 15 per cent of the crop has needed spraying to control Helicoverpa.
To reduce the chance of resistance increasing, the recommended window for using synthetic pyrethroids has narrowed from mid-December to the beginning of February. “The bigger the gap we can have between when the chickpea use ends at the end of spring and when cotton use begins in the middle of summer, the more effective the gap in the selection pressure is to prevent further development of resistance,” Ms Leven explains.
She says chickpea growers usually only need one application of insecticide a season, but the recent spate of wetter, milder springs has prolonged the growing season, “which does mean it is more likely to need a second application. More frequent use over a longer period of time increases the selection pressure, building up the risk of resistance.”
Ms Leven says there are not many products registered for use against Helicoverpa in chickpeas. “This is in part where we think the problem may have emerged from; there are very few product choices available in chickpeas.”
Tom Wilson and his father Bob grow chickpeas, faba beans, wheat, cotton and occasionally sorghum at Wee Waa in northern NSW. So far, he has not experienced a Helicoverpa-resistance problem in their chickpeas and beans.
“Last year we only sprayed two-thirds of our faba bean crop for Helicoverpa and the other third we didn’t touch at all, we didn’t have insect pressure there.” However, their chickpeas got two sprays, due to a second egg-lay.
Before spraying, Mr Wilson looks very closely at the insect pressure on his crop. “Every crop is different with the threshold of how many grubs per metre. That is what we go off, on grub counts.”
With his chickpea crop now emerging, Mr Wilson is considering what effect the growth in resistance will have on his management program. He usually sprays the faba bean crop, which has a short window for Helicoverpa, first. “We will use a synthetic pyrethroid in our beans and if we have resistance problems there, we will then use more. We do have a bit of a test case to see how it goes.”
Mr Wilson is well aware that it does not take long for Helicoverpa resistance to build. “I don’t know how much it will impact on us directly this year, but as the years go on, if the industry as a whole doesn’t make a stand and start changing the chemistry around, it is going to become a big problem,” he says.
Dr Lisa Bird,
02 6799 2428, firstname.lastname@example.org;
02 6792 4088, email@example.com
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