Resistance Update on the Road

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The Resistance Roadshow visited regional areas during late August and presented the latest resistance monitoring results for a suite of important pests. Presentations covered resistance to conventional insecticides in cotton aphids, mites, silverleaf whitefly and helicoverpa, and helicoverpa resistance to the Bt toxins in Bollgard II.

Photo: Downs agronomist Bernie Caffery (right) discusses resistance with Sharon Downes and Grant Herron at the Dalby Resistance Roadshow.

Aphids and mites
Dr Grant Herron, Industry and Investment NSW based at Menangle, presented his latest results for cotton aphids and mites. Cotton aphid resistance to neonicotinoids was detected at many locations during the 2008-09 season and was associated with product failures. Grant suggests that neonicotinoid seed dressings are influencing the development of this resistance. His recommendation is to try to avoid foliar neonicotinoids for aphid control if a neonicotinoid seed dressing has previously been used that season. However, if they are sprayed for aphid control Grant highlighted the need to alternate chemical groups for seed dressing and first foliar spray.

Fortunately there appears to be no cross resistance to pirimicarb, organophosphates and endosulfan and these products should perform satisfactorily against neonicotinoid resistant strains. Cotton aphid resistance to Pegasus® was reported for the first time.

Resistance was detected to Comite® in two spotted mite populations. This is one of the most widely used products for mite control in cotton, so the detection of resistance is a serious concern.

Results of resistance testing for silverleaf whitefly (B biotype) by Zara Ludgate, QPIF Toowoomba, indicate no immediate concerns for the two key products, Admiral® and Pegasus®, used to manage this pest in cotton. Surveys of cropping regions during autumn and winter 2009 have so far failed to reveal any Q biotype Bemisia tabaci that was first reported from north Queensland in late 2008 and north-western NSW in 2009.

According to Dr Louise Rossiter, Industry and Investment NSW, Narrabri, resistance in Helicoverpa armigera to most conventional insecticides has declined or stabilised. Areas of concern are the continuing high level of resistance to older pyrethroids and moderate resistance to the carbamates. Field performance of these products against H. armigera may be highly variable. There are no conventional insecticide resistance issues associated with H. punctigera.

Bt resistance
Dr Sharon Downes, CSIRO Narrabri, and Kristen Knight, Monsanto Australia, outlined the results for resistance testing to the two Bt toxins. While the frequency of Cry 1Ac resistance alleles remains at very low levels, the frequency of Cry 2Ab resistance alleles in populations of H. armigera and H. punctigera are higher than expected. Changes in the frequency of resistance alleles are being closely monitored as further upward movement in resistance frequencies could be a trigger for changes to the Resistance Management Plan which aims to preserve the usefulness of this GM technology.

Photo: Kristen Knight (left) of Monsanto discusses Bt resistance with Kate Charleston of QPIF at the Dalby Resistance Roadshow.