Arboriculture & Urban Forestry 40(6): November 2014 water stress was therefore evaluated as average chlorophyll fluorescence for the early part of the experiment during the time that EAB and other indigenous borers were active. Differences among watering regimes were evaluated with ANOVA fol- lowed by Tukey’s post hoc multiple means com- parisons, with a 95% family-wise confidence level. At the end of the first summer, trees were prepared for overwintering in a cold frame and were watered during any week without precipitation that the tem- perature went above 12.8°C. To determine the devel- opmental stage of EAB and whether development depended on tree water stress, half of the trees were sacrificed and assessed in April 2010. This number included 21 trees that had died or were severely injured by treatments and exposure to borers during the first summer of the experiment, as evidenced by leaf loss, canopy thinning, and basal epicormic growth, plus 27 of the remaining 75 surviving trees. This group of 48 trees evaluated aſter the first year was comprised of 12 trees from the full, 12 from the half, and 24 from the low watering treatments. The remaining 48 living trees were moved to a common garden at a Maryland Department of Agriculture (MDA) facility in Cheltenham, Mary- land, U.S. (N 38°43’52.7”, W 76°50’3.1”), which was near the center of the Maryland EAB Eradication Zone (Sargent et al. 2010). Trees were moved to this site to allow completion of borer development and evaluate EAB voltinism. To facilitate observation of emerging EAB, prevent the escape of EAB into the eradication zone, and prevent additional borer attack, boles of trees were enclosed in fiberglass window screening (New York Wire, Grand Island, New York, U.S.) fastened to the tree with duct tape and 3.18 cm fiberglass pipe insulation (Frost King and Thermwell Products, Co., Inc., Mahwah, New Jersey, U.S.; Figure 1). The trunk above the first scaffold branch, and major scaffold branches (1–2 cm diameter) were enclosed in 1.91 cm polyeth- ylene pipe insulation (Frost King and Thermwell Products, Co., Inc., Mahwah, New Jersey, U.S.; Figure 1). EAB purple prism traps hung within 50 m of the common garden and monitored weekly did not capture any EAB throughout the period of the study. Watering treatments were reinitiated, and new plastic water excluders were placed as before on May 19, 2010. Using tree condition as a guide, water restrictions were suspended on trees in the half and 335 low watering treatments periodically throughout the summer due to extreme heat. Once the EAB flight period ended, as indicated by trap data and observa- tions made by MDA, screening and insulation were removed. Trees and insulation were examined for emerging borers. Watering treatments were main- tained until October 4, 2010; trees were then over- wintered following the same protocols as in 2009. The ability of the screening and pipe insula- tion protocol to prevent borer colonization during the second summer was verified with cage control trees. Four potted green ash trees (DBH ≈ 7.6 cm) were obtained on May 13, 2010, from a nursery in Delaware, U.S., located outside the EAB quarantine zones. These trees were fitted with screening and pipe insulation and placed in a wooded site known to be heavily infested with EAB (Brandywine, Maryland, U.S., N 38°42’17.6”, W 76°53’57.5”). On July 21, 2010, aſter EAB flight ended, these control trees were transported back to the MDA facility and placed in the common garden with experi- mental trees for the duration of the experiment. Identification of Borers Throughout the experiment, live ash trees were monitored for signs of EAB and other borers. In- sects emerging from live trees and caught in the enclosures were documented and then destroyed. Harvested trees were removed from their pots and the root ball was cut off. Bark was removed on the bole as well as on the trunk and branches 1 cm in diameter and larger with a 25.4 cm draw knife. Borers were identified with the aid of MDA staff and in ref- erence to Johnson and Lyon (1994), Solomon (1995), Herms (2007), and Kalisch and Baxendale (2010). With the exception of EAB, borers were identified to the family according to the following guidelines. Emerald ash borer Individuals were identified by the presence of ser- pentine, frass-packed galleries, actual beetles or parts of beetles, or D-shaped exit holes. EAB life stage was recorded to determine generation time. Individuals not attaining the fourth larval instar or prepupal stage by winter do not successfully com- plete development in one year but instead feed through a second summer and emerge the following spring (Duan et al. 2010). Life stage in the spring was therefore used as an indicator of generation time. ©2014 International Society of Arboriculture
November 2014
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