142 Hubbard and Potter: Managing Calico Scale Infestations injury. Soil injection seemingly is well-suited for horse farms or other sites where spray drift is a concern. The first trial evaluated imidacloprid applied through soil injection when trees were dormant, targeting postoverwin- tered nymphs and adults and the subsequent generation of settled crawlers. We used rows of infested sugar maples (10 to 13 cm [4 to 5.2 in] diameter) along a horse farm lane, blocking seven replicates of treated and control trees by vi- sual estimate of initial infestation level. Treated trees re- ceived imidacloprid (Merit 75 WP; Bayer, Montvale, NJ) at the high label rate (1.96 g [0.07 oz] product per 2.54 cm [1.02 in] trunk diameter) either on 19 December 2001, or 3 March 2002. A Kioritz 100 soil injector (Wilbur-Ellis, Seattle, WA) was used to inject the insecticide/water solution (64 g prod- uct/L [8.5 oz/gal]; 11.8 mL/cm [1 fl oz/in] trunk diameter) approximately 15 cm (6 in) deep in a circular pattern around the drip line of treated trees. Adult female scales were sampled on 6 May 2002, 138 days and 64 days, respectively, after the 19 December or 3 March treatments. On these relatively small trees, most adults were situated on basal portions of lower branches and along the main trunk; therefore, live scales were counted on the main trunk to 3 m (9.9 ft) height and on the basal 30.5 cm (12.2 in) of the lowest four branches. Settled crawlers were examined on 17 June 2002 (180 days and 106 days, respec- tively, after the December or March treatments). Fifty leaves were collected from throughout each tree’s canopy and num- bers of dead and total crawlers, and percentage mortality, were analyzed as before. We also evaluated high-volume soil injection with imida- cloprid in late autumn to control calico scale the next growing season. Twelve red maples (approximately 10 cm [4 in] di- ameter) were paired according to the previous year’s infes- tation level. The soil around one tree of each pair was treated with imidacloprid (Merit 75 WP) at 1.96 g (0.07 oz) product per 2.54 cm (1.02 in) of trunk diameter (the highest label rate) on 25 November 2003. A high-pressure injection system (Kappa-55 3-piston pump; Udor, Italy) with a 1.9 cm (0.76 in) diameter wand having four 2.38 mm (0.95 in) holes at right angles was used to apply 1.92 L (64 fl oz) per tree with 147.9 mL (4.44 fl oz) applied per injection point and 13 injection points located 25.4 to 30.5 cm (10.16 to 12.2 in) from the trunk and evenly spaced around the tree. Injection pressure was 7.0 kg/cm2 (100 lb/in2). Efficacy against the overwintering generation, nymphs of which were present when the injections were done, was evaluated on 10 May 2004 (167 days after injections). We counted live adult females on the main trunk to 2.3 m (7.6 ft) height and 46 cm (18.4 in) along four main branches beyond the point of attachment to the trunk. Counts were totaled per tree and compared between treatments by paired t-test. Con- trol of subsequent crawlers on leaves was evaluated on 10 August 2004 (259 days after injections). For those samples, a ©2006 International Society of Arboriculture pole pruner was used to harvest 16 woody twigs with foliage throughout each tree’s canopy. Live and dead settled crawlers were counted on the left half of the abaxial surface of one fully expanded leaf per twig. Data were pooled within trees and analyzed as described earlier. RESULTS Foliar Sprays Targeting Settled Crawlers Acephate, bifenthrin, and carbaryl gave excellent (90% to 100%) control of settled crawlers on individually sprayed shoots (Table 2, trials 1 and 2). In contrast, 2% horticultural oil was only marginally effective, even with complete spray coverage. Insecticidal soap partially suppressed young settled crawlers treated during June 2001 (33 days after first crawler hatch), but was ineffective against older crawlers treated dur- ing July 2002 (55 days after first crawler hatch). Pyriproxy- fen, too, was ineffective with July 2002 treatment timing. Total (live and dead) crawlers did not differ between treat- ments, indicating that dead crawlers remained on the leaves (Table 2). Pyriproxyfen was more effective with earlier treatment tar- geting relatively young settled crawlers. Application on 23 June 2003, 29 days after first egg hatch, resulted in 88.6 ± 3.9% settled crawler mortality compared with 99.4 ± 0.4% from cyfluthrin and 4.8 ± 1.2% mortality within the controls (F 385.3; df 2,14; P < 0.0001; Table 2, trial 3). Preventive Sprays at First Crawler Hatch Bifenthrin or pyriproxyfen applied at first egg hatch reduced numbers of live settled crawlers on leaves by 93% and 63% relative to untreated control branches. Mean (±SE) number of live crawlers per leaf sample from those treatments averaged 85 ± 106, 425 ± 140, and 1142 ± 273, respectively (F7.46; df 2,10; P 0.01). Targeting Postoverwintered Scales with Insecticidal Oil or Antitranspirant Spraying individual hackberry branches to runoff with 2% or 3% horticultural oil on 12 March, before budbreak, failed to control scale infestations on the bark. Infestation levels were comparable on twigs assigned to the different treatments, averaging 64.5 ± 12.1 per 1.9 m (6.3 ft) of twig length. Mortality averaged 56.6 ± 5.5, 68.2 ± 9.2, and 53.2 ± 7.3 for untreated, 2% and 3% oil, respectively, with no increase from the oil sprays (F 6.75, df 2,17; P 0.30). Similarly, spraying whole hackberry trees with horticultural oil on 6 March failed to provide significant control. Scale densities per 2.54 m (8.4 ft) of twig length averaged 322 ± 69 and 344 ±76(F 0.05; df 1,11; P 0.83) and percentage mortality averaged 39.9 ± 4.2 versus 40.8 ± 5.2 (F 0.01; df 1,11; P 0.91) for untreated versus treated branches, respectively.
July 2006
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