Arboriculture & Urban Forestry 32(4): July 2006 143 Table 2. Efficacy of foliar insecticides applied at label rate for scale insects (see text) against settled calico scale crawlers on leaves of individually sprayed shoots. Trial and treatment Insecticidal soap Horticultural oil Bifenthrin Acephate Insecticidal soap Pyriproxyfen Horticultural oil Bifenthrin Acephate Carbaryl Pyriproxyfen Cyfluthrin Crawlers per shootz Trial 1, treated 23 June 2001, on sugar maple Control 544 ± 126 482 ± 87 515 ± 80 478 ± 99 638 ± 161 Trial 2, treated 22 July 2002, on hackberry Control 1375 ± 192 1230 ± 151 1388 ± 303 1930 ± 843 1139 ± 208 1328 ± 361 855 ± 132 Trial 3, treated 23 June 2003, on hackberry Control 1609 ± 230 982 ± 135 1291 ± 368 Percent mortalityy 27.7 ± 4.5 50.0 ± 7.8* 54.5 ± 7.9* 96.8 ± 1.9* 100.0 ± 0.0* 10.2 ± 2.5 7.7 ± 1.8 8.7 ± 1.6 54.5 ± 13.4* 90.2 ± 3.2* 99.2 ± 0.3* 100.0 ± 0.0* 4.8 ± 1.2 88.6 ± 3.9* 99.4 ± 0.4* Adjusted percent mortalityx 0.0 ± 0.0 32.6 ± 7.5 37.7 ± 9.7 94.4 ± 2.8 100.0 ± 0.0 0.0 ± 0.0 0.7 ± 0.7 2.8 ± 0.4 50.2 ± 14.0 89.0 ± 3.7 99.1 ± 0.3 100.0 ± 0.0 0.0 ± 0.0 87.8 ± 4.3 99.4 ± 0.4 zMean total crawlers does not differ significantly among treatments in any trial (two-way ANOVA, P > 0.32). yANOVA results: trial 1: F 79.3; df 4,35; P < 0.001; trial 2: F 91.4; df 6,40; P < 0.001; trial 3: F 385.3; df 2,14; P < 0.0001. xAbbott’s (1925) formula used to adjust for mortality in untreated controls. Data are means (± standard error); efficacy was evaluated 18, 13, and 38 days after treatment in trials 1−3, respectively. Within trials and columns, means followed by an asterisk (*) differ significantly from the untreated control (Dunnett’s test, 0.05). Spraying overwintered nymphs on branches with 2% hor- ticultural oil or 5% Transfilm solution on 29 March failed to reduce the number maturing to adults, but the high (10%) rate of antitranspirant resulted in 33% suppression, significant by Dunnett’s test (P < 0.05) from the untreated control. Live adult scales per 47 cm (18.8 in) of twig averaged 76.5 ± 19.1 on control branches versus 59.7 ± 14.1, 80.7 ± 12.7, and 51.4 ± 12.0 for oil, low and high rates of Transfilm, respectively (F 3.15; df 3,27; P 0.04). Trunk-Injected Systemic Insecticides Versus Whole-Canopy Sprays Whole-canopy sprays with bifenthrin approximately 1 week after first egg hatch resulted in significant (65.6%) mortality of calico scale crawlers in sugar maples as compared with 28.9% natural mortality in controls (Table 3, trial 1). Trunk injection with dicrotophos in late June, however, did not pro- vide significant control in the same trial. When sweetgum trees were injected in late July (trial 2), significant control was obtained from dicrotophos, but not imidacloprid. Neither treatment, however, resulted in significantly lower adult populations on treated trees the next spring (Table 3). Neither imidacloprid nor dicrotophos (injected in late May or early July, respectively) controlled crawlers on sweetgum trees in trial 3, but canopy sprays with bifenthrin gave some suppres- sion (Table 3). Dicrotophos provided partial control on zel- kova in trial 4, but imidacloprid again was ineffective (Table 3). Total (live plus dead) crawlers did not differ among treat- ments in any trial, confirming that initial infestations were comparable and that dead crawlers remained on leaves. Whole-Tree Treatments with Soil-Injected imidacloprid Imidacloprid injected around the drip line using the Kioritz soil injector on 19 December 2001, or 3 March 2002, failed to control calico scale on medium-sized sugar maples. Mean (±SE) numbers of swollen females maturing on sampled branches in May 2002 were 229 ± 132, 203 ± 116, and 153 ± 67 for control trees and the December and March treat- ments, respectively (F0.13; df2,20; P0.88). Simi- larly, neither treatment timing reduced subsequent numbers of crawlers on leaves (2952 ± 1544, 1653 ± 814, 3,000 ± 1111, respectively, per sample; F0.41; df2,20; P0.67) or increased the percentage of dead crawlers by mid-June 2002 (9.3 ± 2.1, 8.0 ± 0.9, 9.7 ± 0.9%, respectively; F0.44; df2,17; P0.66). High-volume, basal soil injection with imidacloprid in late November 2003 also failed to control calico scales on sugar maples. On 10 May 2004, treated trees had an average of 318 ± 86 adult females on sampled branches versus 118 ± 45 for controls (t1.69; df5; P0.15). In August, live settled crawlers on leaves averaged 677 ± 189 per sample for treated ©2006 International Society of Arboriculture
July 2006
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