Chemical control and disease reservoir studies of the wheat curl mite (Aceria tosichella Keifer), vector to wheat streak mosaic virus

Abstract

Wheat streak mosaic virus (WSMV) causes yield loss to wheat (Triticum aestivum) in all areas of the world where the crop is grown. No chemical controls for the WSMV vector, the wheat curl mite (WCM, Aceria tosichella Keifer), are approved. Control relies primarily on avoiding a 'green-bridge' of living plant material that can host the disease between seasons. This study aimed to 1) identify chemical treatments for WCM control under conventional and organic systems and clarify misconceptions that treatments, such as sulfur, control WCM and 2) analyze the capacity of 20 grassy species to serve as reservoirs of WSMV and WCM. The effects of insecticides with varying modes of action (carbamate, organophosphate, pyrethroid, neonicotinoid, biological control, oil, ovicide, mite growth inhibitor, and soap) on WCM population growth were tested in the greenhouse. Treatment with the active ingredients aldicarb and chlorpyrifos decreased WCM populations compared to untreated controls (p<0.001 and p<0.001). Field trials were conducted in spring wheat in 2013 and winter wheat in 2013-2014. Similar effects on WSMV spread were not observed in field trials. These trials included ten products consisting of five modes of action: organophosphates, pyrethroid, oil, soap and mite growth inhibitor. Chlorpyrifos was included in the field trials, but no efficacy was seen in 2013 compared to controls under good infection and incidence and infection was low in 2014, therefore we were unable to distinguish any treatment effect. To assess the capacity of 20 grassy species to serve as reservoirs of WSMV and WCM, plants with varying lifespan and origin were grown in the greenhouse and infested with viruliferous WCM. Lifespan had the greatest impact on ability of plants to host WCM (p=0.011) and WSMV (p<0.001). Annual plant species are more likely to host WCM than perennial grasses, with all species hosting WCM. Native and introduced species tested did not differ in ability to host WCM (p=0.735) and WSMV (p=0.096). This study provides evidence of potential for use of active ingredient chlorpyrifos in WCM control, and showed that lifespan is an important determinant of WSMV disease reservoir potential of grassy species.