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Harvard Forest Symposium Abstract 2008

  • Title: Evaluating chemical treatments of hemlock woolly adelgid in southern New England
  • Primary Author: Christine Rollinson (Oberlin College)
  • Additional Authors: David Orwig (Harvard Forest)
  • Abstract:

    Currently many public and private forest managers use chemical treatments to control hemlock woolly adelgid (HWA; Adelges tsugae) infestations. These treatments are usually foliar sprays of insecticidal soaps and oils or systemic applications of imidacloprid via soil and root drenching or direct injection into the trunk. Although the use of these chemicals is common and widespread, little research has been done on the long-term effectiveness of these treatments. This study looks at a total of 99 hemlocks from four different locations in southern New England that had HWA infestations for at least 5 years prior. At each location, trees had received either foliar sprays of oil or insecticidal soaps or systemic chemical treatments of imidacloprid and were in close proximity to untreated trees. All trees were assessed for live crown ratio, vigor, crown transparency, amount of new growth, amount of HWA wool, and sisten density on new growth. All treatments were effective in maintaining hemlock health and reducing the degree of HWA infestations compared to untreated trees, but systemic treatments performed better than spray treatments. A single systemic application was still effective at reducing HWA 4 years later. Spray success depends on several factors including tree health, surrounding HWA densities, climatic conditions, and frequency of application. The high density of sistens on new foliage on trees treated repeatedly with sprays, suggests that monitoring and continued applications will be necessary in areas with warmer winters and with high overall HWA infestation levels. Results suggest that chemical treatments, when applied early, are an effective solution to controlling HWA infestations and preserving hemlock health in select groves and specimen trees.

  • Research Category: Invasive Plants, Pests & Pathogens