On the effect of ozonated water on mortality of Tetranychus urticae (Trombidiformes: Tetranychidae) on Capsicum annuum (Solanaceae) in greenhouse conditions

Pesticide-resistant populations of the two-spotted spider mite, Tetranychus urticae Koch, have been reported in many countries. This problem has led to the search for alternative control methods. One of these alternative strategies is aqueous ozone. During a series of preliminary test, the effect of different concentrations of aqueous ozone on mortality of T. urticae on pepper (Capsicum annuum L.) was evaluated in greenhouse conditions at 25 ± 2 °C; 50 ± 5% RH and 16:8 (L:D) photoperiod. Then efficacy of ozone to control the pest was evaluated in different experimental conditions including three exposure times (5, 10 and 15 seconds), different time of spraying (8 am, 2 pm and 8 pm), and different ages of the host plant (4, 8 and 12 weeks old). Each experiment was carried out in a randomized complete design with six replications. Based on the screening tests, ozone concentration of 43 g/m3 was found to give efficient results in terms of mortality rates of the mites and morphological traits of the host plant. The mortality rate of the mites increased with increasing exposure time. Although the interaction effect between ozone concentration and exposure time was significant, in other experiments, no significant difference in the mortality percentage of the mite among either times of application, or ages of the host plant was found. In none of these experiments, no symptom of injury to the host plant foliage such as chlorosis, necrosis, yellowing or malformation was observed after aqueous ozone spraying. Based on these results, aqueous ozone at a specific concentration and conditions can reduce the population density of T. urticae without any visible damage on the pepper foliage. However, more research needs to be done before ozonated water can be deployed commercially as a pesticide.