 |
 |
|
The dangers of decay
A vigilant manager can help safeguard trees from damage or loss.
 |
Photo courtesy of John Fech |
Decay comes in many forms, but for golf course managers, the only thing worse than tooth decay is tree decay. If some of the trees on your golf course are looking a bit shaggy, look a little closer – they may be worse off than you think.
When decayed, trees can be disfigured or die, which results in a loss of amenity and function for the course. The advantages of shade, cooling, beauty, pollution prevention and erosion control are lost when trees and tree growth are compromised.
Decayed trees can also cause damage to people, property and buildings that are nearby. During wind storms, branches can fall from trees; sometimes the entire tree can blow over. In other situations, branches fall and trees topple over even without significant winds. If golfers wander from the fairway to look for errant balls, they might fall victim to a blow on the head from a falling branch.
The good news is that steps can be taken to maintain healthy trees and to limit damage to buildings and injury to people from trees.
What causes decay?
Any action – whether from man or nature – that breaks a limb or damages the bark can cause decay. When the bark is broken, inner sapwood and heartwood tissues are exposed. Once exposed, these tissues are no longer protected from infection from decay organisms. The organisms are generally considered to be ubiquitous, ever present in sufficient quantity to cause decay. Once the protective bark is broken, fungal spores are carried to the tree through wind and splashing rainstorms, and decay begins.
Decay is a slow and steady process. As you might expect, hardwood trees such as walnut, hickory and red oak are more resistant to decay than softer-wooded species like silver maple, poplar and cottonwood. Decay progresses at a faster pace with soft woods that are surrounded by warm and humid weather conditions.
Site inventory and inspection
How do you know if your trees are decaying? The best way to find out is through a site inventory. Start by identifying older, soft-wooded trees and inspect them. The older a tree is, the more susceptible it is to decay. Look closely for decay entry points: torn/broken limbs, mower-gouged trunks and, my favorite, 5-iron damage from frustrated golfers.
Unfortunately, it’s not easy to tell if a tree has internal decay. It’s not like a broken leg that can be X-rayed or examined through magnetic resonance imaging. (Actually, such a tree inspection device – the Resistograph – exists, but it costs about $5,000 and can provide only limited information in terms of overall evaluation of the tree.)
The best device to determine what’s on the inside of a tree trunk or branch is a little lower tech than the Resistograph – a screwdriver. I’ve found that the best model is the one that comes in a 14-piece set that never gets used because it’s the largest one, and you just don’t have screws that big. I’ve checked many a tree with my trusty Craftsman slotted screwdriver. Other common items that would work well include a sharpened piece of rebar or a headless golf club. Most superintendents have easy access to broken golf clubs that could be easily adapted. A bonus to using a modified golf club is that it’s easy to manipulate because it has a grip.
Probe the tree with the sharpened end of your favorite tool. Entry points are often soft and “punky” on the outside, with the decay extending into the tree for several inches. Probe each suspected area of infection, pushing hard to determine the extent of the decay. The threshold for deciding whether a limb should be removed or a tree left to stand on the course is the ratio of solid wood to soft wood. If more than a third of the internal heartwood and sapwood is decayed, then the branch or trunk is suspect and should be considered for removal.
Unfortunately, inspecting for internal decay is difficult. Several factors can confuse the process. First, areas of decay rarely develop in small, easily identifiable shapes, such as circles or ovals. Commonly, they resemble irregular fungal disease patterns that infect turf, such as summer patch.
Second, they extend vertically in the sapwood and heartwood, not just horizontally. Infection begins where the trunk or branch is exposed and spreads vertically as the tree continues to grow in circumference. It is quite possible for decay organisms to initiate decomposition in tissues on the average of 6 to 12 inches per year.
Finally, because even very small breaks in the bark can allow decay organisms to enter the sapwood, significant decay can be present without any exterior symptoms. This explains why cutting off a small tree branch can reveal large areas of internal decay that seem to be inconsistent with the size of the cut.
Tree responses to decay
Fortunately, trees were created with survival mechanisms that can resist the spread of decay. The primary process is calledcompartmentalization.
Trees usually respond to wounding by “walling off,” or compartmentalizing, the tissues infected with decay organisms. This process is used by the tree to resist the spread of decay and infection, confining it to the wood present at the time the wound was made. The result is a protection of future growth areas, including the all-important vascular cambium.
The response to wounds causes chemical changes, some of which are visible as wood discolorations. These wound responses are generally protective for the tree, but discoloration reduces the value of the wood for lumber. Because most golf course trees are not intended for harvest, this is not of great consequence.
Hire it out
A good management option for many superintendents is to hire a consulting arborist to provide assistance with diagnosis. When it comes to hiring an arborist, think in terms of three general categories of expertise. Each provides a valuable service, so choose according to the need at hand.
Mow-and-blow arborists perform various tasks such as debris removal, lower limb removal and stump grinding.
Licensed arborists prune, fertilize and control pests on trees. They have passed an examination by the local municipality to document a basic level of proficiency and usually have liability insurance, are bonded and have first aid/CPR training.
Certified arborists are all of the above and have received additional training in cabling, bracing and pest diagnosis. The certification is through the International Society of Arboriculture or the state arborists association. The ISA certification process is similar to the GCSAA certification process.
Preventing decay
Once decay is established in a tree, there are no effective control measures, either to stop it or to limit its spread. Sure, you can cut an infected limb off, but this creates a larger wound and a bigger opening for future decay.
In the 1960s, ‘70s and ‘80s, many “tree surgeons” routinely painted cuts and wounds with tar, spackle and various wound dressings to keep out decay organisms. Unfortunately, scores of university and Forest Service studies have concluded that these products do not prevent decay, and in some cases, actually enhance it. Occasionally, (and regretfully) a few uninformed arborists are still engaged in this practice.
Because decay is not directly treatable, every step should be taken to prevent it. Any action that injures a tree is likely to cause decay.
Consider all golf course maintenance procedures for their impact on tree health and vigor. When pruning, try to use the concept of “target pruning” as your guide. Start by making an undercut on the branch to be removed, then make another cut a couple of inches outward toward the end of the stem. The first cut reduces the chance of ripping and tearing the bark on the trunk, and the second cut removes the weight of the branch.
Next, identify the branch bark ridge and the branch collar, which are present on all trees except palms. The third and final cut removes the branch stub, which should be made just outside the branch collar.
Decay entrance through pruning cuts is obvious; however, mowing and mulching are other common practices that should be considered. The phenomenon of “mower blight,” where unskilled or uncaring operators allow the mower to strike tree trunks, is an all-too-common occurrence. In most situations, the effects are cumulative, with the operator allowing the mower to strike the tree repeatedly over the growing season. Each individual impact is not too damaging, but added together, the injury is significant.
Mulching is normally considered to be a practice that is conducive to healthy tree growth. Mulch helps to retain soil moisture, suppress weed growth and keep the soil cool. However, as with many things in life, too much of a good thing is problematic. Proper application involves the correct depth and placement of the material.
In most plantings, a 2- to 3-inch layer of organic, wood chip-type mulch is preferred. Mulch should be placed over the soil, beginning 3 to 6 inches away from the trunk, and extending as far out into the golfscape as is practical. The material should not contact the tree trunk. If mulch is piled around the trunk, diseases such as armilaria root rot are likely to occur. It is highly desirable for the mulch to extend out to the drip line of the trees.
Finally, become knowledgeable about proper tree maintenance. Many opportunities for continuing education exist through the GCSAA and the ISA.
RECENT issues
 |
 |
April |
March 2006 |