Bulb Mite Control in Easter Lilies

Bulb mites, (Rhizohlyphus robini, Claparede) have been an Easter lily (Lilium longiflorum, Thunb.) pest since at least the 1890s.  They appear to thrive in the southern Oregon/northern California coast’s damp and warm weather pattern.  Bulb mites feed on both bulb and root tissue, and while damage may occur in field grown plants, damage is more easily and commonly seen at the greenhouse forcing stage where the bulb mites tunnel into the bulb stem causing stunted plants, flower blasting, leaf deformation, or complete stem breakage. Bulb mites also feed on stem roots causing an overall weakness in plants.  Kelthane WSP (active ingredient dicofol) has been the most effective treatment for bulb mites in Easter lilies over the last few decades; this product has the added benefit of having no known dermal sensitivity to handlers, making it safe to use.  However, Kelthane WSP will soon no longer be available for ornamental use in the United States.  The objective of this study was to determine the effectiveness of possible new pesticide options for controlling bud mites.  Treatments included: 1) Kelthane WSP [dicofol]; 2) Cinnacure [cinnamaldehyde]; 3) Cinnacure + Safer Soap 1%[potassium salts of fatty acids]; 4) Sporan [rosemary oil]; 5) EF 500 [plant essential oils]; 6) Sanmite [pyridaben]; 7) Terraclor [PCNB]; 8) Promite [fenbutatin]; 9) Akari [fenpyroximate]; 10) Floramite [bifenazate]; 11) Kontos [spirotetramat]; 12) Safer Soap 2%; 13) a wash in water followed by Safer Soap 2%; 14) a wash in water; and 15) an unwashed bulb control.  Test bulbs were dipped in the treatments for 30 minutes and then either sent for immediate mite extraction and counting or potted up and grown to full maturity following all routine commercial greenhouse protocols. Only Safer Soap at 2%, Terraclor, and Akari were as good or better at controlling bulb mites as the industry standard of dicofol.   In the greenhouse setting, percent plant emergence was similar for all treatments, except for EF 500, which was slower than other treatments for emergence, and Akari and Kontos which showed better than average emergence.  In the greenhouse, early growth had increased symptoms of plant chlorosis with Promite, Akari and Terraclor compared to other treatments.  Sporan and the washed bulbs had the highest bud counts.  While results are promising for some of these products, continued experiments are needed to extend labeling or pinpoint usage rate of these pesticides for greenhouse-grown Easter lily production.