American Arborvitae, Spruce Spider Mite Control, Richland Co., Ohio, 1979

Abstract

Abstract Thuja occidentalis (2.5-3 m high) growing in a nursery on 1.2 m centers in 2 rows ca 150 m long were used to evaluate acaricides against spruce spider mite, Oligonychusununguis (Jacobi). Treatments were assigned to trees at random, but an effort was made to distribute each treatment over a 50 m section of row. Treatments were applied with a KWH mistblower operating at 420 ml/min. Six trees were sprayed with each treatment for 30 sec. on July 30 under sunny skies at 27-29°C, with an 8-16 kph breeze. Application required 9 man-hours. On Aug 10, half of the trees (3) in each treatment were sprayed again for 30 sec, as before. Ambient temperature was 27-29°C with cloudy skies and a 16-24 kph breeze. The second application, when only half of the trees were sprayed and all were already flagged and tagged, required 4 man-hours. Treatment effectiveness was evaluated 2, 3, and 4 weeks after the first application. During each evaluation, 10 branch ends 15-18 cm long were selected from the tree from between 1 and 2 m above ground and transported in plastic bags in an air conditioned vehicle to the laboratory. Twenty-five tips (5-7.5 cm long), comprising ca 400 sq cm, were clipped from the 10 branch ends from each tree for population assessment. Each tip was passed through a mite brush 6 times to dislodge mites to a rotating glass plate coated with Tween-20. Living and dead nymphs and adults trapped on 8 of 12 equal sections on the plate were counted. Counts were multiplied by 1.5 to calculate mites/unit area of foliage. Each evaluation required collection of foliage from ca. one-third of the trees during a morning, drying foliage in the laboratory, and processing the samples the same day, to minimize mite mortality between the time samples were taken and counts were made. Sample collection each day required 1 man-hour; each sample (rep.) was processed in one-half man-hour.