L. K. Tanigoshi, B. S. Gerdeman and G. Hollis Spitler
Washington State University
Mount Vernon Northwestern Research and Extension Center
Mount Vernon, WA 98273-4768
Yellow spider mite field trial.
Population levels of spider mites in northwestern Washington exceeded expectations given the unseasonably cool, wet spring and early mild summer temperatures. This in contrast to 2007 when spider mite populations were generally non-economic ones, especially in northwestern Washington. Problematic flare-ups of the yellow spider mite (YSM),Eotetranychus carpini borealis, were particularly severe in the Northwood area of Lynden where late May population on both ‘Meeker’ and ‘Willamette’exceed our provisional treatment level of 25 motile life stages per leaf by 10 to 100-fold. Female YSM emerge from diapause earlier and disperses earlier than the twospotted spider mite (TSSM) from mid-April to May. This species migrates to distal primocane foliage along the top trellis wire of red raspberry in April to May. Our research data has shown the YSM prefers cooler spring and fall temperature. The onset of warm weather combined with stressed foliage provided the right conditions for a mid-season (May to August), region wide flare up of mostly YSM and lesser levels of the TSSM and European red mite on the distal half of the canopy bearing most of the developing flower buds.
On 8 July 2008, we field-tested two rates of the recently registered Acramite 50WS (bifenazate) and Acramite 4SC and experimental Envidor 2SC (spirodiclofen) with Vendex™ (fenbutatin-oxide) on a mature ‘Meeker’ site in Lynden, WA. Envidor is a Group 23 acaricide. Applications were applied with our plot spray equipped to deliver 133 gpa at 1.8 mph with 2 D4-45 Tee Jet nozzles on top of boom, with 2 D2-25 nozzles pointing up into the row while both vertical arms were equipped with 14 D3-25 Tee Jet nozzles. Treatments were replicated five times and plots measure 30 feet long by 10 feet wide. Twenty-five leaflets were taken at random from primocanes at chest height from both sides of the row. These samples were processed with a mite brushing machine. Compared with the untreated check, empirically all miticides performed comparably to each other and all were significantly different from the untreated check out to 37 DAT (Table 1).