Arboriculture & Urban Forestry 32(4): July 2006 141 (300 lb/in2) pressure. Approximately 23 L (6 gal) of tank mix was applied to each canopy. Control trees were not sprayed. Twigs were collected from throughout the lower half of the canopy of each tree on 24 March and cut into 12.7 cm (5.1 in) lengths. Twenty pieces were randomly selected from each tree and examined as previously mentioned. Total live and dead scales and percentage mortality were analyzed as be- fore. Another trial evaluated some arborists’ anecdotes that spraying postoverwintered nymphs with a horticultural anti- transpirant (Transfilm; PBI/Gordon, Kansas City, MO) might control calico scale. Transfilm is an emulsion of polyethyl- enes and polyterpenes that, according to its label, coats the leaf surface to reduce water loss from transpiration and plant stress during storage, shipping, and establishment. Horticul- tural oil (2%) was included for comparison. Treatments, in- cluding controls, were applied to separate tagged branches (1 to 3 cm [0.4 to 1.2 in] diameter, 1 m [3.3 ft] long) blocked within 10 heavily infested sweetgum trees. The antitran- spirant was mixed with water at medium (5%) and high (10%) label rates. Treatments were applied on 29 March 2005, when nymphs were small, flat, and gray and evaluated in the field on 22 April 2005, by counting numbers of live, swollen black and white females on the first 46 cm (18.4 in) of twig length located apically beyond the tag. Trunk-Injected Systemic Insecticides Versus Whole-Canopy Sprays Four trials were done to evaluate timing and efficacy of trunk-injected systemic insecticides for managing calico scale. The Mauget MicroInjection System (J.J. Mauget, Arcadia, CA) wherein therapeutic chemicals in sealed cap- sules are introduced through tubes inserted into shallow holes (4.0 mm [0.16 in] diameter) drilled in the root flare (Tattar et al. 1998), was used for trunk injections. Products evaluated were 82% dicrotophos (Inject-a-cide B [bidrin]; Mauget; 2 mL [0.06 fl oz] capsules) and 10% imidacloprid (Imicide; Mauget; 4 mL [0.12 fl oz] capsules) at label rate: one capsule per 5.1 cm (2 in) of trunk diameter. For comparison, two of the trials included whole-canopy sprays with bifenthrin (Talstar Lawn and Tree Flowable, FMC, Philadelphia, PA) at label rate (Table 1). The bifenthrin tank mix included a sur- factant, as before, and was applied with the same hydraulic spray unit described for the whole-canopy oil applications. Imidacloprid was injected earlier than other treatments be- cause it can take as long as 1 month to fully translocate to leaves (Tattar et al. 1998), whereas dicrotophos translocates in a few days and bifenthrin has immediate contact activity. Untreated control trees were included in each trial. Trees were assigned to treatments (i.e., blocked) by visual estimate of initial infestation level. Trial 1 compared activity of whole-canopy bifenthrin sprays applied soon after crawler hatch versus trunk-injected dicrotophos targeting relatively young settled crawlers. Treat- ments were replicated five times using heavily infested sugar maple trees (25 to 36 cm [10 to 14.4 in] diameter). Bifenthrin sprays were applied on 29 May 2001, 8 days after the first crawlers were observed. Dicrotophos was injected on 28 June 2001. Fifty leaves were sampled from throughout the lower half of the canopy of each tree on 15 July 2001, 47 and 17 days, respectively, after the spray or systemic treatments. All live and dead crawlers were counted, and percentage mortal- ity was determined as before. Trial 2 compared efficacy of injected dicrotophos and imi- dacloprid against settled crawlers on sweetgum leaves. Treat- ments were replicated four times with separate trees (25 to 46 cm [10 to 18.4 in] diameter) as replicates. Trees were injected on 31 July 2002, 66 days after first observed crawler hatch. Efficacy was evaluated on 28 September (59 days after treat- ment) by sampling 25 leaves from throughout the lower half of each tree’s canopy and examining all settled crawlers. The same trees were sampled again on 19−20 May 2003, to evalu- ate any differences in subsequent adult populations. Twenty 50 cm long twigs were arbitrarily sampled from each tree canopy. Numbers of adults were counted and compared among treatments as before. Trial 3, conducted from May to September 2003, used cultivated, heavily infested sweetgum trees (25 to 40 cm [10 to 16 in] diameter, five replications per treatment). Treat- ments were imidacloprid and dicrotophos injected at the aforementioned rates, plus bifenthrin whole-canopy sprays and untreated controls. Imidacloprid was injected on 23 May, 2 days before first crawler hatch, whereas dicrotophos and bifenthrin treatments were on 2 July. Efficacy was evaluated by sampling 25 leaves from throughout the lower half of the canopy of each tree on 7 August 2003, and counting dead and total settled crawlers per sample. Trial 4, also conducted in 2003, compared imidacloprid injected on 20 May (5 days before crawler hatch) versus dicrotophos applied on 2 July for controlling calico scale crawlers in a stand of zelkova trees (15 to 25 cm [6 to 10 in] diameter). Treatments were randomly assigned to five trees per treatment blocked by infestation level. Efficacy was de- termined by sampling 100 leaflets from each tree on 22 July 2003, and counting crawlers as before. Whole-Tree Treatments with Soil-Injected Imidacloprid Imidacloprid is labeled for soil injection for systemic control of sucking insects on woody plants. Label directions specify that injection holes be in a grid or circular pattern extending to the tree’s drip line or else be evenly spaced around the trunk no more than 15 to 30 cm (6 to 12 in) from its base. The label states that because translocation may take 60 days or longer, applications should be made before anticipated pest ©2006 International Society of Arboriculture
July 2006
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