Evaluation of the efficacy of non-pesticide substances to control two spotted spider mite (Tetranychus urticae) on strawberry

Strawberry is an important crop of high economic value in Taiwan, and it is one of reasons farmers invest a lot of money to develop facility cultivation such as nethouses, greenhouses and plant factories. However, the crop is threatened by several tiny pests both in the field and greenhouses. Among them, the two-spotted spider mite (Tetranychus urticae) is one of the most common and serious pests of strawberry. Chemical control is a conventional method for controlling the mite, but there are some problems with using pesticides to control T. urticae. Pesticides can cause serious problems such as resistance in T. urticae populations and residues on the fruit. Therefore, it would be beneficial to find some safer and more efficient non-pesticide substances for pest control on strawberry. In this study, narrow-range oils, and wood-vinegar, soap, and sugar-vinegar solutions were tested for their efficiency in controlling T. urticae on facility-cultivated strawberries. The results of the dish test indicated that narrow-range oils and the soap solution at a 200-fold dilution produced the highest mortality rates among these non-pesticide substances with respective mortality rates of 58.3% and 61.7%, but these were lower than that of abamectin (98.3%). Moreover, in the potted strawberry test, mortality rates of narrow-range oils (88.3%) and the soap solution (86.7%) at a 200-fold dilution were very high after 72 h of treatment. In the control experiment, respective control rates for narrow-range oils and soap solution at a 200-fold dilution were 91.1% and 84.2%. This indicates that T. urticae was efficiently controlled using these substances. Moreover, results showed that the wood-vinegar solution at a 200-fold dilution produced a low mortality rate, but it still had the some control effect on the T. urticae population. The control rate with the wood-vinegar solution was 62%. It is suspected that some other factors suppress the population density of T. urticae. In the future, narrow-range oil and soap solutions will be applied to control mites on strawberries in greenhouses and plant factories.