December 2024.
Recent molecular testing by the NSW DPIRD has confirmed etoxazole (Zeal®) resistance in two-spotted spider mites collected from northern NSW. This finding comes at a difficult time for crop managers in this region who are already facing challenges with mite management due to diafenthiuron and abamectin resistance.
The target site mutation responsible for this resistance has been found in approximately 10% of the mites tested from last season. As confronting as this sounds there is some good news in that the gene responsible for resistance is recessive. This means that offspring that only carry one copy of the resistance gene are fully susceptible to etoxazole. All mites that have tested positive for this resistance gene have been heterozygotes (only carrying one copy). However, these individuals are still ‘sleepers’ within the population, carrying resistance that isn’t yet being expressed.
The major risk going forward is that overuse of etoxazole may increase the proportion of these heterozygote mites, which in turn increases the chance that these individuals will mate together. On average, one quarter of the progeny from each of those matings will be homozygous mites (carrying 2 copies of the gene) that are likely to survive field applications of etoxazole.
With the usage of etoxazole likely to be high in the 2024/25 season due to resistance for other products and low availability of propargite (e.g. Comite®) there is a clear risk of this form of etoxazole resistance may take hold. This finding does not change the IRMS for the 2024/25. Commencing control of threshold level mites between squaring and early flowering with etoxazole remains a sound approach. However, when used, etoxazole must be applied to achieve maximum effectiveness.
Read the full article and key steps for maximum effectiveness here.