Arboriculture & Urban Forestry 36(3): May 2010 * Root flare soil drench treatments of PBZ would reduce bacterial leaf scorch disease symptoms. * Using an adjuvant, trunk-applied anti-bacterial chemicals or growth regulators would reduce bacterial leaf scorch disease symptoms. * Root flare injections of oxytetracycline antibiotic would reduce bacterial leaf scorch disease symptoms. * An optimal time for springtime oxytetracycline injections to have maximum effect on bacterial leaf scorch disease could be determined. MATERIALS AND METHODS All experiments were conducted on mature Quercus palustris (pin oak) in and around Lexington, Kentucky (38°N, 84.5°W), at several different locations within 5 km of Lexington. Disease severity evaluations were made on each indi- vidual tree by estimating the amount of foliage with scorch symptoms as a percent of total foliage. Each tree was eval- uated by a single observer taking data from all sides of the tree. In most of the experiments, disease severity rat- ings were also done the year before at roughly the same date so that comparisons could be made from one year to the next. To visualize these comparisons, data are pre- sented graphically so that disease severity can be seen as a percent of the previous year’s disease severity. For sta- tistical comparisons, analysis of absolute values of dis- ease severity and areas under the disease progress curve (AUDPC) were also made. Results were statistically ana- lyzed using the Waller-Duncan LSD Mean Separation Test. PBZ Drench Treatment Experiment 1 The experiment was established on pin oaks with varying lev- els of bacterial leaf scorch growing on the Idle Hour Country Club golf course in Lexington. Ten golf course oaks, average diameter at 1.4 m above ground (DBH = 94 cm), were treated July 2003. At the time of treatment, a shallow trench encircl- ing the base of the tree was dug around the buttress roots and trunk. PBZ was applied at labeled rates to the trench at the base of the oaks. Each tree was paired with a tree of similar age, placement, and condition which was treated only with wa- ter. The experiment was designed as a randomized complete block with 10 replications. Oaks were evaluated in October 2003, October 2004, October 2005, and October 2006. Symp- toms of leaf scorch on each tree were observed and a percent- age incidence was assigned for each. Photographs were also taken so that tree health progress could be noted over the years. Experiment 2 The experiment was established on pin oaks with vary- ing levels of bacterial leaf scorch growing as street-side trees in several Lexington neighborhoods. During Au- gust 2003–October 2003, the oaks (average DBH = 78 cm), were treated with PBZ or used as water-treated con- trols as previously described. Annual disease evaluation re- cords were completed 2003–2005 as previously described. 141 Surfactant-Assisted Treatment Eighty street-side pin oak trees, average DBH = 75 cm, grow- ing in a Lexington neighborhood with a history of bacterial leaf scorch disease were selected for this experiment. Trunk treat- ments were applied July 13–14, 2005, and where two treat- ments were required, repeated August 24, 2005. Treatments were applied to all surfaces of individual tree trunks from ap- proximately 5 cm above the ground to a height of approximately 2 m using a hand-pumped backpack sprayer (Solo® News, VA, U.S.) delivering spray at a pressure of 1.8 kg/cm2 , Newport . Each tree trunk received 1.5 L of suspension. The PBZ basal drench treatment was applied as previously described, on July 19, 2005. The eight treatments (Table 1) were replicated 10 times and the experiment was established in a randomized com- plete block design. Prior to treatment applications, while foliage was still green, trees were evaluated for dieback (an indicator of chronic leaf scorch) in early July 2005, so that trees repre- senting varying stages of disease could be distributed equally among the treatments. On September 27, 2005, and again Octo- ber 19, 2006, trees were evaluated for percent scorch symptoms. Antibiotic Root Flare Injections For all injection treatment experiments, pin oaks for use in ex- perimental plots were evaluated for bacterial leaf scorch when symptoms were prominent the year before treatment applica- tions. From these data, trees with varying levels of leaf scorch (0%–100%) were equally assigned to each treatment group so that no treatment was compromised by use on predominantly heavily diseased trees and compared with another treatment used on predominantly healthy trees. Prior to 2006 treatments (Experiment 1), oaks were evaluated for scorch on October 18, 2005; and prior to 2007 treatments (Experiments 2 and 3); oaks were evaluated on October 18 and 19, 2006, respectively. Experiment 1 To test the efficacy of therapeutic treatments in 2006, plots were established at Stone Street Farm in Lexington, a horse farm with a history of bacterial leaf scorch disease. Eighty pin oaks (aver- age DBH = 55 cm), lining a long driveway and growing along the boundaries of the farm, were selected for this experiment. Based on data from the previous year (2005), average leaf scorch was 30%–36% for each treatment group. Therapeutic treatments com- pared injected antibiotics and injection methods to soil drench and trunk applications for reducing bacterial scorch symptoms. The eight treatments (Table 2) were applied during June 2006, and replicated 10 times in a randomized complete block design. In 2006, trees were evaluated for percent leaf scorch symp- toms on August 15; September 6 and 21; and October 3 and 18. Oxytetracycline hydrochloride (Bacastat™ OSC, Rainbow Treecare Scientific Advancements, Minneapolis, MN, U.S.) or oxytetracycline phosphate (Bacastat OSP, Rainbow Treecare Scientific Advancements, Minneapolis, MN, U.S.) antibiotics were injected using one of two methods: 1) a macro-infusion technique, or 2) a micro-injection technique. Macro-infusions were made following the protocol developed by Rainbow Tree- care Scientific Advancements. Infusion sites were made 13–20 cm below the tops of root flares through 0.6 cm holes drilled into the basal flare roots which were exposed by removing soil around the base of the tree with an air excavator (Supersonic Air ©2010 International Society of Arboriculture
May 2010
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
