1) SUMMARY
Spider mites, especially two-spotted spider mite (Tetranychus spp.) have on occasion (the latest being Crop Years 1995 and 1996) been a severe problem in sugar beets, especially in the Fall Plant/Summer Harvest Areas of the San Joaquin Valley. Mites feed on leaf surfaces and reduce the photosynthetic capacities of the plant. Mite colonies can reduce sugar and tonnage or lead to defoliation at high population levels.
It is not fully understood why the problem occasionally occurs; however, shifts in planting dates relative to cotton, milder weather, the use of broad spectrum pesticides, and mite resistance to miticide are probable causes for the outbreaks.
2) CURRENT PEST MANAGEMENT PRACTICES
Control Measures: Various populations of two-spotted spider mite have been shown to be resistant to propargite (Comite®), fenbutatin-oxide (Vendex®), and dicofol (Kelthane®). These are the primary acaricides that have been used for 20 to 40 years to control spider mites in crops throughout the San Joaquin Valley. Newer acaricides such as Zephyr® have been registered in cotton, ornamentals, and strawberries but are not registered in sugarbeets. Currently, sugarbeet growers have available sulfur and the organophosphate naled (Dibrom®) for spider mite control, and both products are relatively ineffective in controlling two-spotted spider mite. Efforts are underway to obtain registration of additional acaricides for sugarbeets. Information is needed to determine if sugarbeet spider mites are resistant to older acaricides such as Comite®. For newer acaricides such as Zephyr®, even if a registration is obtained for sugarbeets, there is the potential for resistance to develop because Zephyr® is already being used heavily in neighboring crops such as cotton. Thus, sugarbeet growers need a long-term solution to the management of spider mites that reduces their dependence on acaricides.
Biological Control: Biological control of spider mites using predatory mites such as Galendromus occidentalis, Neoseiulus californicus, and Phytoseiulus persimilis has been very successful in various tree crops, greenhouse vegetables, strawberries, and vines. Research is needed to see what species of predatory mites are currently found in San Joaquin Valley sugarbeets and to determine if springtime augmentative releases could be used to manage spider mites problems.
Host Plant Resistance: None available.
3) REDUCED-RISK OPTIONS
Resistance management for spider mites is a key element in sugarbeet IPM. Successful programs have been demonstrated worldwide with spider mites, and resistance management has been developed in California cotton. The key is applying materials only when needed as determined by scouting, using sound treatment triggers, rotations of materials and rotating between materials with varying modes of action. For example, in cotton, even though resistance exists in spider mites for Comite® and difocol, susceptibility is being maintained by limiting applications to once per year per compound and using Zephyr®. Key to spider mites resistance management in sugarbeets will be the availability of products with different modes of action. The lack of these compunds only hastens the resistance problem.
Spider mites outbreaks are related to seasonal factors, regional cropping patterns, and insecticide use in the sourrounding area. Knowledge of these factors is very limited but could provide the keys in developing areawide, multiple crop management programs. Current understanding is very limited, and more thorough studies will be required.
4) CHALLENGES
To assess interaction between armyworm control and secondary pests such as mites and leafhoppers.
5) INNOVATIVE FEATURES IN REDUCED-RISK PROGRAM
No information available.
6) BARRIERS TO ADOPTION OF REDUCED-RISK METHODS
No information available.