Winter Oil Spray to Control Fletcher Scale on Taxus, 1987

Abstract

Abstract An experiment was conducted in a commercial nursery in Broad Brook, Hartford County, Conn., to determine the effectiveness of a late-winter application of oil for controlling Fletcher scale on taxus and the degree of phytotoxicity caused by subfreezing temperatures following application. On 11 Mar, 30 1-m yews (15 each of'Densiformis' and 'Hicksii') heavily infested with Fletcher scale (x = 50 scales/12-cm branch) were randomly assigned to 3 groups. Two groups were treated that day with Scalecide 1:50 dilution (245 oz [AI]/100 gal); the other group served as the untreated check. Treatments were applied by a Solo Jetpak 425 backpack sprayer. Two liters of mixed solution was applied to each tree in 1 group, sufficient to drench the plants completely. Half as much mixed solution was applied to each tree in the other group, which provided only partial coverage of the plant. All living scales were second-instar nymphs at the time of treatment. Air temperature at the time of application and continuously for 12 days hence was monitored using a Foxboro hydrothermograph located on the ground among the treated trees. On 9 Apr each of the 30 yews was examined for phytotoxicity. The percentage of the total branches on each yew and the percentage of the total needles on an average branch on each yew that showed phytotoxicity were categorized in increments of 25%, Symptoms of phytotoxicity included yellowing, browning, and desiccating foliage. Each yew was sampled by removing 10 randomly selected 10-cm-long branches from the inner and outer positions of the crown. Branches were examined by microscope and the first 5 scales encountered on each branch were recorded as dead or alive. Air temperature at the time of application (12:15 to 2:00 P.M.) was 3.9°C (39°F), but within 5 h it fell below freezing, reaching a low of -3.3°C (26°F) overnight. During the subsequent 11-day period, daytime temperatures rose above freezing every day and fell below freezing on 8 nights. The maximum and minimum temperatures recorded for the period were 15.6°C (60°F) and -3.9°C (25°F), respectively.