Two-spotted spider mite in Cyprus: ineffective acaricides, causes and considerations

Growers of greenhouse roses in Cyprus have recently reported failures of several acaricides against two-spotted spider mite (Tetranychus urticae Koch). To verify the cause of these failures we evaluated the effectiveness of seven acaricides against two rose and two cucumber spider mite populations in the laboratory. The acaricides included in our study represented the most important mode of action groups registered for use in greenhouses on the island. Label rates of all seven acaricides (abamectin, clofentezine, dicofol, fenbutatin oxide, fenazaquin, propargite and milbemectin-a product under registration) caused close to 100% mortality in the cucumber populations, but significantly lower mortality in the two rose populations. Mortality never exceeded 65% in the first rose population and 20% in the second population for any acaricide, suggesting development of resistance. The higher frequency of acaricide applications in roses and the perennial nature of the crop, that sustains genetically similar populations for long periods of time, may have facilitated the development of resistance. Judicious use of newer acaricides with distinct modes of action as they become registered may help control resistant spider mite populations in roses and other ornamental crops. Additionally, adoption of a mode of action labeling scheme of pesticides and training of growers on alternation of products will facilitate long term sustainable spider mite management in Cypriot agriculture.