growers@sgcotton.com.au Roger Tomkins - Greenmount Press

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The changing face of aphids and mites in Australian cotton ■■By■Grant■Herron,■Senior■Research■Scientist,■NSW■DPI,■Camden There has now been a long history of resistance monitoring for both aphids and mites from Australian cotton with much of this being done by our team at NSW DPI. Mites Up until 1980, both bean spider mite and two-spotted mite were collected and tested for resistance, but for 30 years bean spider mite disappeared from Australian cotton. This is unusual because normally bean spider mite will displace two-spotted mite. The reason probably relates to two-spotted mite’s ability to develop resistance. For instance, bean spider mite resistance to the OP monocrotophos never exceeded about 10 fold, yet twospotted mite resistance to the same chemical was often hundreds of fold (Figure 1). This gave two-spotted mite a huge advantage over bean spider mite in heavily sprayed cotton and bean spider mite disappeared. Jump forward a few decades and the cotton ecosystem is dominated by Bt cotton and the sprays are all but gone. Now bean spider mite again has the advantage over two-spotted mite and in theory it should start to displace it. Anecdotally this is exactly what seems to be happening with mite samples collected by myself in Queensland invariably containing bean spider mite while two-spotted mite is more abundant in NSW. The reason for this NSW preference is not clear, as two-spotted mite is still quite resistant to some chemicals, but fortuitously not to its mainstay control Comite (Figure 2). The bean spider mite resurgence is complicating the laboratory based resistance testing because bean spider mite will displace two-spotted mite in the lab prior to testing being done. Additionally, if it happens that again bean spider mite needs to be tested for resistance, the chemicals used in cotton are now different to what they used to be. reference baseline data for newer chemicals is not available and this baseline information would have to be generated. Finally, the damage done to cotton by bean spider mite looks different, less severe. Bean spider mite is likely a whole new management ball game. PhD student Kate Marshall with PhD supervisor grant Herron testing neonicotinoid resistant cotton aphid. Aphids Aphid problems in cotton up until the mid 1990s were little more than deciding what to spray. At the end of 1998 a resistance issue developed in cotton aphid with resistance detected to all registered chemicals used for its control. The biggest loss to resistance was the IPM friendly chemical Pirimor. In laboratory tests with high level resistant aphids, the product could surround and cover aphids like snow but do nothing. Figure 1: Monocrotophos resistance detected in two-spotted mite (Tetranychus urticae) and bean spider mite (Tetranychus ludeni) between 1976 and 1994 Figure 2: Percent strains of cotton aphid containing propargite (e.g. Comite) resistant individuals between 2004–05 and 2011–12. NB: No strains tested in 2009–10. 20 — The Australian Cottongrower August–September 2012
2013 FARM STUDY TOURS For More Information Contact: David Dowling 0417 703 169 or Lloyd O’Connell 0428 724 615 travel@greenmountpress.com.au – www.greenmounttravel.com.au
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growers@sgcotton.com.au Roger Tomkins - Greenmount Press

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