Arboriculture & Urban Forestry 47(2): March 2021 of beneficial organisms to insecticides will help sup- press GS populations (Frank et al. 2013; Frank and Dale 2019). Various chemical products can be used to aid in gloomy scale management. Application of horticul- tural oil during crawler activity in the spring and/or during the dormant season are common recommen- dations for armored scales. Insect growth regulators (e.g., pyriproxyfen) can also provide effective man- agement of gloomy scale and other armored scales (Rebek and Sadof 2003; Raupp et al. 2008; Frank and Dale 2019). However, these treatments must be made when crawlers are present, and full coverage of the plant must be achieved. Systemic products allow for additional “forgive- ness” relative to topical products because they can be applied prior to scale emergence, and the residual may last through the entirety of the crawler emer- gence and settling phase. One of the most commonly used groups of systemic insecticides in the green industry is the neonicotinoids, which includes acet- amiprid and dinotefuran. These products can be applied as a foliar, basal bark, and/or soil drench application. These products are effective for armored scale manage- ment (e.g., Cowles 2010) and can be excellent options in areas that do not have restrictions or bans on their use (Buzzetti et al. 2015; Frank and Dale 2019). Caution must be taken when applying neonicotinoids, because their presence has been detected in nectar and leaves in the following year post-application (Mach et al. 2018). A relatively recent pest management product intro- duced to the green industry is flupyradifurone. Flupyradifurone is a group 4D insecticide with a rel- atively favorable toxicological and ecotoxicological profile and different structural properties than other insecticides of this group (Jeschke et al. 2015; Nauen et al. 2015). Unlike group 4A products that can be soil-applied, bark-applied, or injected, flupyradifu- rone does not appear to translocate through xylem of large trees, but will move upward into the foliage in smaller herbaceous plants like soybean (Stamm et al. 2016). Flupyradifurone, however, will translocate in smaller, container-grown woody plants or when foliar- applied to lateral branches via apoplastic xylem trans- port (Nauen et al. 2015). Foliar applications of flupyradifurone have been shown to be very effective in the management of several piercing-sucking pest systems such as aphids (Nauen et al. 2015; Lahiri et al. 2019), mealybugs (Ganjisaffar et al. 2019), psyllids 65 (Chen et al. 2017), scales (Grafton-Cardwell and Scott 2015), and whiteflies (Nauen et al. 2015; Roditakis et al. 2017). The purpose of this study was (1) to quantitatively compare the effectiveness of two generally recom- mended chemical treatments for gloomy scale, the combination of pyriproxyfen plus horticultural oil and dinotefuran alone, and (2) compare flupyradifu- rone with these two generally recommended treatments. Additionally, we sought to (3) assess the flexibility of flupyradifurone with regards to the post-settling phase of GS crawlers. As stated previously, in order to treat effectively for GS with products, applications of pyriproxyfen plus horticultural oil should be made once crawler activity is detected. The crawler activity window can be 6 to 8 weeks long, and crawlers will gradually emerge over that time. Issues can arise when property owners contact pest management specialists after this window. In these instances, practitioners will likely have to wait until the following growing season to treat for GS. Therefore, we wanted to explore the potential for the use of flupyradifurone at other times during the growing season to evaluate the efficacy of this product outside of the traditional treatment win- dow. We present the results of a study comparing differ- ent products and timing for the management of GS. MATERIALS AND METHODS Research Site We selected 54 semi-mature, GS-infested red maple trees located along the street right-of-way at the Walkers Ridge Community in Rock Hill, South Car- olina, USA, with permission from the Walkers Ridge Home Owners Association. All trees were planted over a 2-year period between 2008 and 2010; there- fore, the trees in this study were between 9 and 11 years old. Backe and Frank (2019) found that trees did not become infested with GS until at least 7 sea- sons after trees are planted. Additionally, they reported a delay between the first observation of GS and a noticeable decline in tree health. The A. rubrum at this site were visibly infested with GS but not yet displaying a decline in tree health. Trees that were maintained by adjacent homeown- ers, trees that we did not have permission to include in this study, trees that were in poor condition upon visual inspection, and trees that did not readily appear to have high densities of GS were not included. ©2021 International Society of Arboriculture
March 2021
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