64 Chase et al: Gloomy Scale Management Arboriculture & Urban Forestry 2021. 47(2):64–71 https://doi.org/10.48044/jauf.2021.006 URBAN FORESTRY ARBORICULTURE Scientific Journal of the International Society of Arboriculture & Horticultural Oil, and Dinotefuran Against Gloomy Scale ( Efficacy of Flupyradifurone, Pyriproxyfen and Comstock) By Kevin D. Chase, Elden LeBrun, and Chad M. Rigsby Abstract. Gloomy scale (GS)(Melanaspis tenebricosa) is a major pest of red maple (Acer rubrum) across much of the eastern USA. Current pesticide recommendations for GS management are efficacious when applications are made at the appropriate time. However, appropriate tim- ing may not always be possible. For instance, the tree owner may not contact pest management professionals in time to make timely applica- tions. We established a field trial to determine the efficacy of the pesticides pyriproxyfen plus horticultural oil and dinotefuran, as well as a relatively new pesticide available in the ornamental woody plant market, flupyradifurone, against GS. There were three primary goals of this study: (1) to quantitatively compare the effectiveness of pyriproxyfen plus horticultural oil and dinotefuran; (2) to compare flupyradifurone with these two generally recommended treatments; and (3) to assess whether flupyradifurone is effective when applications are made later in the summer. We found that pyriproxyfen plus horticultural oil, dinotefuran, and flupyradifurone applications made during the active crawler period were equally efficacious, statistically, and that flupyradifurone treatments applied later in the summer were not statistically differentia- ble from untreated controls. While these pesticide applications are effective at suppressing GS populations, plant health care tactics aimed at preventing outbreaks should be prioritized and incorporated into the complete pest management strategy. Keywords. Armored Scale; Pesticide Trial; Urban Trees. INTRODUCTION Red maple (Acer rubrum L.) is among the most com- monly planted trees in the urban landscape through- out the eastern and central United States (Raupp et al. 2006). The popularity of this species stems from its ability to tolerate a variety of environmental condi- tions, its fast growth rate, and its autumn coloration (Frank et al. 2013). There is a wide range of A. rubrum cultivars available from the nursery industry. How- ever, these trees can be afflicted with issues such as micronutrient deficiencies in alkaline soils, the for- mation of girdling roots, sun scalding, and structural defects due to codominant stems (Gilman and Wat- son 1993). The dominant insect pest afflicting A. rubrum, spe- cifically in southeastern and mid-Atlantic states, is gloomy scale (GS), Melanaspis tenebricosa Com- stock (Hemiptera: Diaspididae). GS is an armored scale, which are among the most difficult insects to manage in urban landscapes (Braman et al. 2015). ©2021 International Society of Arboriculture Tests (i.e., the insect’s armored shells) from previous years remain on bark for several years. They are unsightly and may be confused with honeydew and resulting sooty mold, which is not produced by GS. Dale and Frank (2014) found that A. rubrum in urban settings are especially prone to GS infestations and poor health. Severe GS infestations can kill trees, usually in conjunction with poor cultural practices and inclement weather events. Management recommendations for GS involve cultural, biological, mechanical, and chemical con- trols to varying degrees, depending on site conditions and severity of the infestation (Frank and Dale 2019). For example, choosing a planting site where summer heat will not be amplified by buildings or parking lots and appropriate watering are good cultural practices. Pruning out infested branches may be helpful when light infestations occur. Practicing conservation bio- logical control, where habitat is provided for natural enemies, while eliminating or minimizing the exposure Melanaspis tene bricosa
March 2021
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