Appendix G Bartlett Tree Research Laboratories Technical Reports

Transcription

1 Appendix G Bartlett Tree Research Laboratories Technical Reports a. Managing Oak Wilt Disease in Pennsylvania b. Oak Wilt c. Emerald Ash Borer in Pennsylvania d. Campus Tree Management e. Phytophthora Root Rot and Collar Rot of Landscape Plants f. Common Oak Scale g. Black Vine Weevil h. Young Tree Pruning i. Girdling Roots j. Root Collar Disorders k. Mulch Application Guidelines l. Preventing Construction Damage to Trees m. Boxwood Management Plan n. Lightning Protection for Trees o. IPM of Clearwing Borers p. Spider Mites: A General Discussion q. IPM for Landscape Plants r. Pest Management of Flowering Dogwood s. Maintenance Pruning Standard: A Simplified View

2 Managing Oak Wilt Disease in Pennsylvania Bruce R. Fraedrich Ph.D. Bartlett Tree Research Laboratories The incidence of oak wilt disease appears to have increased dramatically in forests and landscapes throughout western Pennsylvania in The disease is caused by the fungus Ceratocysitis fagacearum that colonizes the vascular system of many oak species causing wilting, branch dieback and death of affected trees. Symptoms: Species in the red oak group are highly susceptible to oak wilt disease. Symptoms first appear as bronzing and wilting of the leaves in the upper canopy. Leaves then turn brown along the margins and often appear water soaked. This is followed by shedding of most of the leaves, many of which drop when they are still green. Red Oak Group (Quercus spp.) Red oak Q. rubra Black oak Q. velutina Scarlet oak Q. coccinea Pin oak Q. palustris Blackjack oak Q. marylandica White Oak Group White oak Q. alba Bur oak Q. macrocarpa Swamp white Q. bicolor oak Chestnut oak Q. prinus Trees can die within a few weeks after the onset of symptoms although recovery occasionally occurs. Species within the white oak group exhibit some resistance to oak wilt. Affected portions of the crown display leaf bronzing, browning, wilting and defoliation. The disease progresses slowly through the crown, and branch dieback and decline may occur over a period of years. Recovery of affected trees occurs more frequently than in the red oak group. Brown streaks may be present beneath the bark on wilting branches. This discoloration is most common in species in the white group. Figure 1: Decline and defoliation from oak wilt. Figure 2: Brown streaks within sapwood of oak wilt affected branches. Bartlett Tree Research Lab, Charlotte NC January 2005

3 Disease Transmission Insects are responsible for transmitting the oak wilt fungus over long distances to establish new infection centers. Once a new infection is established, the fungus moves rapidly from tree to tree through root grafts that occur between oaks of the same group. Long distance spread: The oak wilt fungus produces spore mats beneath the bark on diseased oaks in the spring following the year that they died. As these spore mats mature, they exert pressure on the bark tissues, which provides an opening for insects to access the fungus pathogen. The mats emit a fruity odor that attracts certain species of sap beetles (Nitidulids). These beetles become contaminated with spores of the oak wilt fungus when they visit the mats. Nitidulids then transmit the fungus when they feed on sap from wounds on healthy oak trees. Most new infections from Nitidulids occur in mid-april through June when spore mats form on dead oaks and wounds on healthy oaks are most receptive to infection. New infections can also occur from July through September, but this is considered a low risk period. Oak bark beetles can also carry the oak wilt fungus. These insects breed in the inner bark and sapwood of dying and recently killed oaks. Bark beetles transmit the fungus when broods emerge from infested diseased trees and bore into healthy oaks. Local Spread: Once new infections occur, localized spread takes place through root grafts that form between oaks within the species group. Root grafts can occur within oaks growing within 100 feet of one another and are responsible for rapid expansion of the infection center. Root grafts seldom occur between oaks of different species groups. Disease Diagnosis: Oak wilt may be confirmed through laboratory cultures from diseased branches. Branch samples should be collected from portions of the crown exhibiting early stages of wilt. Because the oak wilt fungus is sensitive to heat, samples should be packed in ice ( cold packs ) and shipped to the diagnostic lab by express mail. Isolation/confirmation of the disease through cultures is difficult and frequently produces false negatives. Disease Management Identify Infection Centers: Surveys to identify the extent of the disease and to identify new infections centers are the first step to disease management. Aerial surveys can be utilized to identify suspected infection centers. Confirmation of the infection centers must then be undertaken by a ground survey. In urban and suburban landscapes, educating homeowners about identification and management of oak wilt will aid in early detection and treatment of the disease. Information can be disseminated through bulletins in water or electric bills, newspaper articles and websites. Cultural Practices: Sanitation: Trees in the red oak group should be removed and destroyed by chipping, burning or burial. Red oak species that have died from oak wilt should be removed before the spring following their death to avoid possible disease transmission. Diseased wood also should not be stored as firewood through the winter. Because spore mats do not form on species in the white oak group, immediate removal and destruction of diseased white oaks is not necessary. Pruning/Wounding: Oaks should not be pruned or wounded from April through June to prevent possible transmission by Nitidulid beetles. Wounds should also be avoided from July through September. If oaks are wounded during this time, a thin coating of asphalt based tree paint should be applied to Bartlett Tree Research Lab, Charlotte NC January 2005

4 reduce the possibility of disease transmission. Maintenance pruning should be scheduled for October through March. Root Graft Prevention: Trenches should be installed between diseased and healthy trees of the same oak group to help reduce root graft transmission of the oak wilt fungus. Chemotherapy: The fungicide Alamo is registered for root flare injection to prevent oak wilt disease. The fungicide can also aid in recovery of diseased white oaks but is not effective as a therapeutic treatment in diseased red oaks. Oaks growing between diseased trees and the primary trench should be treated with Alamo. High value oaks just beyond the primary trench should also be treated. The fungicide Alamo should be injected into symptom-free oaks to help reduce the risk of new infections. Red oaks that display wilt symptoms seldom respond to fungicide treatments but Alamo may prevent further decline and death in white oaks. Figure 3: Diagram showing installation of trenches in relation to diseased trees. Courtesy of Rainbow Treecare Scientific Advancements. Primary trenches should be installed approximately 100 feet from the diseased tree using a vibratory plow, trencher or backhoe. Trenches should be installed to a depth of at least three feet. Secondary trenches can be installed immediately between the diseased and healthy trees to further reduce the potential for spread. If secondary trenches are not installed, removal of symptom-free oaks within the primary trench line should be considered. Stumps should be treated with certain herbicides to kill the roots. If symptom-free trees are not removed, treatment with the fungicide Alamo is the other option. A soil fumigant, Metam-Sodium (Vapam) was once registered for application to the soil to sever root grafts to prevent oak wilt. This product is no longer registered by the United States EPA for this use. No chemical treatment is currently available to sever root grafts. Bartlett Tree Research Lab, Charlotte NC January 2005

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9 Campus Tree Management E. Thomas Smiley, Ph. D., Plant Pathologist Bruce R. Fraedrich, Ph. D., Plant Pathologist There are two ways to run a campus tree management program. The simplest way, in which most programs are run, is by crisis or reactive management. Deadwood is removed when someone complains, trees are planted when donations are received, and fallen trees are cleaned up after a storm. Goals and Objectives: Goals and objectives must be designed in clear, precise and measurable terms. Goals vary among tree managers, with most expressing the desire to have an aesthetically pleasing campus landscape that poses no imminent safety hazards to passer-bys. Crisis management works, it has for years, but is a cost effective way to manage? The alternative is proactive management. This entails defining program goals, determining resources, developing a management plan and implementing the plan. Research has found that crisis management accomplishes work on only one third the number of trees serviced on a proactive management program. Crisis management is a simple process, whose outcome is determined by external factors. The remainder of this article will describe proactive management for campus trees, designed so you can obtain positive results. There are five steps to developing a proactive management strategy: Define program goals and objectives Inventory resources Develop a management plan Implement the plan Follow up with accurate records

10 2 Examples of written goals may be the following: Goal 1: For public safety, trees with potentially hazardous conditions will receive remedial immediate treatments or be removed. Goal 2: To ensure an aesthetically pleasing campus landscape, losses will be minimized with a plant health care program and suitable plant replacements selected. Goals are defined in objectives. The objectives of Goal 1 become: C. Pest populations will be monitored and treated as needed. Specific objectives should be defined for all of the generalized goals. Resource Inventory: This is a listing of resources available, such as people and equipment, as well as an inventory of your trees. There are several ways to accomplish a tree inventory. It may be performed with inhouse staff, temporary summer employees, by contractors or by a combination of the three. Data accuracy, administrative problems and costs vary among options. A. All trees will be inspected for defects and after major storms annually. B. Dead or potentially hazardous trees will be removed within one week of their discovery. C. Hanging or broken limbs greater than two inches in diameter will be removed within two weeks of their discovery. BTRL 12/99 D. Trees will be pruned preventively on a four-year rotation to minimize deadwood and structural problems. E. Young trees will be pruned on two-year rotations for the first ten years after planting to promote sound structure. The objectives of Goal 2 become: A. Tree mortality will be less than 1% of the population. B. High value trees will be fertilized on a two-year cycle. The type of data collected for each tree depends on your program goals. Typical options include: Location Tree/Site Parameters Species, size, condition and interfering utilities Management Needs - Planting site classification, pruning requirements, insects and diseases, sidewalk damage and nutritional requirements. For an inventory to be worth the time and expense of collecting the information, it must be updated and used as a management tool. The only way this can be practically TR-13

11 3 conducted for populations of over 1,000 trees is through the use of computers. Tree management computer software is available for purchase or lease through a number of firms and universities. You may be able to develop a program in-house with the assistance of the college s computer department. It is best to have software developed prior to the inventory to avoid collection of excess information. Management Plan: A management plan can be developed from the information collected in the inventory and based on the stated goals and objectives as listed in step one. It should be a plan of action, describing how your goals will be achieved using resources that are available. It may also show that the stated goals cannot be achieved with the resources on hand, which case alternative goals can be developed and a revised budget prepared. A proactive plan should project work for three to five years. Since many factors will change, the plan will need to be periodically updated and projected to the future. Updating is relatively easy if your department is computerized. Computer summary reports can be prepared showing how much tree work remains to be completed, how much work has been completed, how much work each crew typically performs and how many requests have been received. buildings and windows and large trees in open areas that may attract lightning. Hazardous tree work priorities also depend on the location of the tree. Maintenance can be delayed on trees in low traffic areas, away from sidewalks or buildings. Trees next to buildings and walkways must receive top priority for maintenance. The second major consideration is preservation or tree health. This includes routine pruning to maintain health and structure, irrigating feature trees during droughts, fertilizing on a two to four year schedule, and maintaining insect and disease pests below damaging levels. Integrated pest management programs are recommended to prevent losses from pests while minimizing pesticide usage. The third consideration is aesthetics. Maintaining a desirable natural form of a plant, pruning rather that shearing foundation plantings and maintaining open vistas are some consideration for aesthetics. An aggressive pest management program, which goes beyond plant health management and addresses cosmetic injury, is another consideration. Where budgets allow, planting unusual and rare species creates a campus arboretum. The management plan should clearly define work priorities as it is by following the priority system that work can most efficiently be accomplished. In general, there are three broad classifications of tree work priorities, Safety, Preservation and Aesthetics. With a limited budget, money should be spent first on trees with potentially hazardous conditions. Obvious defects include dead trees, broken and hanging limbs and deadwood. More subtle hazards include lower limbs blocking signs or interfering with pedestrians or vehicles, trunk decay that has structurally weakened the tree, root rots that have decayed major support roots, V-crotches or split crotches, trees rubbing against BTRL 12/99 TR-13

12 4 Implementing the Plan: What is the best way for campuses to get tree work done? It usually involves a mixture of work done by inhouse crews and contract crews. In-house crews can address small tree pruning, less intricate removals, and possibly pest monitoring. If you are unsure of crew skill level, large tree service companies, other private firms or university extension agents can provide training. Quality tree service companies can also do work on small trees and shrubs. Planting can be done in-house during slow times such as in the late fall, winter or early spring. This not only keeps crews busy but also gets planting done at the best time of the year for the tree. In most instances, contracting out maintenance on large trees to tree service companies is most economical. Tree service companies have the necessary equipment and trained personnel to perform this work efficiently. In order to ensure quality work at the best possible price, consider the following: Write very tight (specific) bid specifications, which detail the quality of work desired. The National Arborist Association (NAA) and American National Standards Institute (ANSI) publish standard specifications for all phases of tree maintenance that is essential for developing bid specs. Pre-qualify contractors. Choose only established companies with a solid reputation. Make sure the arborist is certified by the International Society of Arboriculture. Ensure that the contractor carries sufficient liability insurance by requesting an insurance certificate. Ask for and check references, especially of similar sized college or commercial projects. Record Keeping - Document all maintenance performed, including dates and persons/company performing the maintenance. Document all tree surveys and inspections, even those in which no problems/defects were encountered. Update tree inventories annually to reflect changes in the tree population and maintenance performed. This will form the basis for next year s management program. By assuming a proactive approach to tree care on campuses, work can be accomplished more effectively to provide healthier, safer trees at reasonable cost. BTRL 12/99 TR-13

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