Arboriculture & Urban Forestry 36(3): May 2010 fully to assist in the movement of therapeutic phosphite chemi- cals into trees susceptible to sudden oak death disease (Garbe- lotto et al. 2007; Garbelotto and Schmidt 2009). It is possible that phosphite chemistry does not affect X. fastidiosa. For the antibiotics streptomycin and oxytetracycline, there is no assur- ance that surfactant actually moves these materials into the tree. Antibiotic Root Flare Injections None of the antibiotic treatments “cured” infected trees or pre- vented scorch symptoms from appearing by the end of the grow- ing season. This is consistent with previous reports of oxytetracy- cline effects on bacterial leaf scorch of elm (Kostka et al. 1985). However, it is clear that springtime treatment with antibiotic re- duces bacterial leaf scorch and delays summertime scorch symp- tom expression. Based on these results, root flare injection done about three weeks after first leaves are fully expanded appears to be an optimal time. For the 2007 trials (Experiment 2), it is not known whether the spring freeze or summer drought affected the treatments or disease expression. It appeared that healthy leaves remained greener a week or two longer into the fall than normal so final disease evaluations were continued somewhat later in 2007 than in 2006. In the street tree trial (Experiment 3), oxytetracycline hydrochloride results might have been enhanced if the injections had been done in late May, rather than mid June. IMPLICATIONS FOR ARBORICULTURE Management of bacterial leaf scorch in oaks already infected with bacterial leaf scorch is very difficult. Arborists are in need of a remedy for bacterial leaf scorch disease. Although treatments used in this experiment did not cure trees of bacterial leaf scorch, treatments that can delay symptoms by even a few weeks might prolong the useful life of infected trees. These results suggest that by using methods readily available to the industry, symp- toms can be delayed during the growing season. In the experi- ence of the study authors, making repeat treatments on the same tree continues to delay symptoms each year (data not shown), without actually providing a cure. Whether delaying symptoms annually actually extends the useful life of infected trees is not known and would require additional long-term experiments. Arborists should consider using various management prac- tices aimed at extending the longevity of mature specimen trees infected with bacterial leaf scorch. These practices may include treatment with antibiotics, reduction of water stress through proper mulching and timely irrigation, and management of secondary insects and diseases. For future disease manage- ment, it is hoped that a biological control treatment using a be- nign strain of X. fastidiosa can be developed for bacterial leaf scorch of landscape trees. This concept is already being studied for management of Pierce’s Disease of grapes (Hopkins 2005). Replication in tree disease management field trials is a neces- sary step for product and method testing because what may be ef- fective on one or two individual trees may or may not work con- sistently on other trees nearby. Arborists should also appreciate the difficulties of conducting replicated experiments on naturally- infected mature trees in the field because not all trees are uniformly infected at the start of the experiment. For example, in all experi- mental groups in this study, October tree scorch symptoms were highly variable from tree to tree, ranging from no scorch to 100% 145 of leaves showing symptoms. Without adequate replication, this variability can lead to erratic results and difficult statistical analy- sis. This work was done in populations of pin oaks; bacterial leaf scorch of other tree species might not respond in the same way. Acknowledgments. Gale Moore, Stone Street Farm; Eddie Hodges, Idle Hour Country Club; Larry Hanks, Pampered Properties; Bernadette Amsden, Department of Plant Pathology; Stacy Borden, Dave Leonard Consulting Arborist; and Claudia Cotton and Tobias Fullwood, student interns. LITERATURE CITED Anonymous. 1993. Bacterial leaf scorch of landscape trees. Center for Urban Ecology Information Bulletin. National Park Service. Wash- ington, D.C. 4 pp. Beale, J., P. Bachi, and J. Hartman. 2002. Landscape plant disease ob- servations from the plant disease diagnostic laboratory - 2002. pp. 22–23. In: University of Kentucky Agricultural Experiment Station 2002 Nursery and Landscape Program Research Report 468. Bentz, J., and J. Sherald. 2001. Transmission of the xylem-limited bacte- rium Xylella fastidiosa to shade trees by insect vectors. pp. 203–208. In: C. Ash (Ed.). Shade Tree Wilt Diseases. American Phytopatho- logical Society. St. Paul, MN. Brannen, P.M., and J.C. Garner. 2008. Evaluation of products for con- trol of fire blight in Georgia, 2007. Plant Disease Management Re- ports 2:PF019. Accessed 3/11/09. DeStefano, D.A., A.P. Grybauskas, J.L. Sherald, B. Momen, Q. Huang, and J.J. Sullivan. 2007. Effect of the growth regulator paclobutrazol on growth of the bacterial pathogen Xylella fastidiosa. Arboriculture & Urban Forestry 33:246–252. Gould, A.B., G. Hamilton, M. Vodak, J. Grabosky, and J. Lashomb. 2004. Bacterial leaf scorch of oak in New Jersey: Incidence and economic impact. Phytopathology 94:S36. Gould, A.B., and J.H. Lashomb. 2005. Bacterial leaf scorch of shade trees. APSnet. Garbelotto, M., D.J. Schmidt, and T.Y. Harnik. 2007. Phosphite injec- tions and bark application of phosphite + Pentrabark control sud- den oak death in coast live oak. Arboriculture & Urban Forestry 33: 309–317. Garbelotto, M., and D.J. Schmidt. 2009. Phosphonate controls sudden oak death pathogen for up to 2 years. California Agriculture 63: 10–17. Hartman, J.R., C.A. Kaiser, U.E. Jarlfors, B.C. Eshenaur, P.A. Bachi, and W.C. Dunwell. 1991. Occurrence of oak bacterial leaf scorch caused by Xylella fastidiosa in Kentucky. Plant Disease 75:862. Hartman, J.R., Eshenaur, B.C., and U.E Jarlfors. 1992. Shingle oak, a new host for bacterial leaf scorch caused by Xylella fastidiosa. Phyto- pathology 82:498 (abstract). Hartman, J.R., B.C. Eshenaur, and U.E. Jarlfors. 1995. Bacterial Leaf Scorch Caused By Xylella fastidiosa: A Kentucky Survey; A Unique Pathogen; and Bur Oak, A New Host. Journal of Arboriculture 21: 77–82. Hartman, J.R., U.E. Jarlfors, W.M. Fountain, and R. Thomas. 1996. First report of Bacterial Leaf Scorch Caused by Xylella fastidiosa on Sugar Maple and Sweetgum. Plant Disease 80:1302. Hopkins, D.L. 1989. Xylella fastidiosa: Xylem-limited bacterial patho- gen of plants. Annual Review of Phytopathology 27:271–290. Hopkins, D.L. 2005. Biological control of Pierce’s disease in the vineyard with a benign strain of Xylella fastidiosa. Phytopathology 95:S44. ©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
