Update on diamondback moth (Plutella xylostella) insecticide resistance and the vegetable brassica insecticide management strategy

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The susceptibility of field populations of diamondback moth (DBM), Plutella xylostella, to lambda-cyhalothrin, methamidophos, spinosad and indoxacarb collected from the four major brassica-growing regions has been assessed approximately every 2 years from 1997 to 2008. Recent results indicate that populations from all regions have increased their resistance to lambda-cyhalothrin, but there is little or no resistance to spinosad and indoxacarb and reduced resistance to methamidophos. This mitigation of resistance in DBM is attributed to, in particular, a decade-long regional adherence by the vegetable industry of rotating spinosad with indoxacarb in a two-windows-per-year rotation strategy. The original insecticide resistance management rotation strategy had to be updated to incorporate chlorantraniliprole registered as a foliar spray, and recently a mixture of chlorantraniliprole and thiamethoxam as a seedling drench. Seedling drenches have been removed from the twowindow strategy used for foliar sprays, with drenches now aligned with periods targeting the highest pest pressure, allowing mode of action (MoA)-free periods and rotation of different MoA insecticides to mitigate any resistance build-up in DBM.

G.P. Walker
S.I. Davis
F.H. MacDonald
T.J.B. Herman
New Zealand Plant Protection