Economic injury level of date spider mite, Oligonychus afrasiaticus (Acari: Tetranychidae) on six commercial date cultivars

The date spider mite, Oligonychus afrasiaticus (McGregor) (Acari: Tetranychidae) is a destructive pest on date palm trees, causing high economic losses. Here, we investigated the relationship between population density of O. afrasiaticus and the extent of its injury level as well as the relation between rate of damage and date yield losses indices on six commercial date cultivars in five date palm growing provinces including Khuzestan (Sayer and Berhee), Hormozgan (Pyarum), Kerman (Mazafati), Bushehr (Kabkab), and Sistan and Baluchestan (Rabi) of Iran. The experiment was conducted in a complete randomized block design with five treatments and three replications. To this end, in each replication, four date clusters were selected from four different geographical directions, in each of them, 25 fruits were checked randomly to unveil the number of healthy and infested fruits. The sampling was repeated at seven-day intervals from late May to early September. Finally, the Norton model was used to estimate the economic injury level (EIL) under both biological and chemical control conditions. The highest value of EIL in 2019 was estimated for Sayer in the chemical control method (1827 Mite-day) and the lowest one was estimated for Pyarum in the biological control method (25.5 mite-day). Our results also revealed that the cost of biological control was significantly lower than chemical control. The highest and lowest rate of date injury (symptoms of the pest feeding) were observed on Berhee and Mazafati cultivars, respectively. Also, the highest and lowest rate of date loss were observed on Kabkab and Sayer cultivars, respectively. On the other hand, the cost of chemical control in both years was higher than that of biological control.