KEEP TREES FREE OF DISEASES BY TAKING CARE OF THEM FROM THE START.
Trees give us so much, oxygen, shade, beauty, shelter and value to our
property, it makes good sense to do all we can to protect our trees from harm.
ROOT GRAFTING of plant tissue, either stem or root tissue,
implies an anatomical fusion between two plants or non-joined parts of the same plant which were not previously connected. Thus, if a root graft has occurred using the above definition, then whatever nutrients, plant growth hormones, plant metabolites, pathogens, assimilates, etc. can move through the plant species through transport in the xylem tissue or translocation in the phloem tissue, should move through the root graft. There are ample published research findings that demonstrate transfer of fungi (oak wilt and Dutch elm disease), herbicides (non-treated trees dies from flashback of chemical through root graft), and metabolites (girdled trees survived for years presumably form root graft transfer) through root grafts.
Click of Photos to Enlarge
A Pecan tree that has formed callus tissue over a Live oak limb. The Live oak tree and limb are very much alive,
producing acorns and not pecans. Photos by Jim Rediker
The fungus that causes oak wilt, Ceratocystic fagacearum, is native to the United States. It affects both the group of trees call "red oaks" (The Live oak and Spanish oak or Texas Red oak ) and the "white oak" group (species include Bur oak, Chinquapin, Monterey oak, Lacey oak and the Post oak). Red oaks are the most susceptible to the disease and usually die within the season that they are infected. White oaks are more tolerant or resistant of the infection due to compartmentalization or water proofing from one cell to the next, in red oaks there is osmosis between the cells. HOWEVER, THE LACEY OAKS AND SHIN OAKS ARE THE EXCEPTION HERE. Inspite of being of the white oak family, they are highly suseptable to oak wilt and there is absolutely no chance of saving these trees no matter what the degree of infection and mortality is very very rapid.
Texas Red oaks (Spanish oaks) and Live oak trees are highly susceptible to a lethal fungal blight, Ceratocystis fagacearum, referred to as oak wilt. Consequently, many Texas residential aresa and ranches have lost and will continue to lose their only shade trees as well as the remaining oak trees in their pastures. For over 25 years oak wilt has wrought ecological and economical havoc on par with that of the Dutch elm disease and the pine bark beetle. Newly infected Red oaks are cut down and destroyed, fungicides are injected into the trees and bull dozers have ripped millions of feet of trenches around the surviving Live oaks to prevent the fungus from spreading from root to root. The damage is estimated in millions of dollars and hundreds of thousands of dollars are being spent for trenches and the instalation of the new bioguard barrier as a means of control that has still not proven to be effective, and yet the real problem, human management of woodlands, and possible capture and sterialization of the nitidulidae beetle, has not been addressed.
1. Underground transmission of oak wilt through root grafts: The fungus spreads from tree to tree in two different ways. Via "root grafts"; when two oak trees of the same species grow close together, their roots tend to grow together and become a shared system, and the fungus is transmitted from one tree to another via the roots. Oaks within 50 feet are potentially at risk for root grafting. The actual distance varies and other factors determine if tree root systems are grafted together. (Root grafting happens most commonly between red oaks; in Texas, stands of live oaks are usually clones that share a single root system). If one of these trees becomes infected, the root grafts serve as natural “pipelines” for the oak wilt fungus to spread, below ground, to the healthy tree. Cutting or severing root systems between diseased and healthy oak trees is an effective way to help stop and/or slow the progression of oak wilt. It is important to understand that trenching will never stop or slow the spread of oak wilt in the Live oak and the Texas Red oak trees because of the overland transmission of the disease by the beetle. However, keep in mind, the beetle is not looking for stop signs or trenches, the next meal is the only priority. The " KESTREL " Propiconazole MEC 14.3% Fungicide injections are also useful to protect trees from oak wilt. Root grafts normally form between oaks of the same species; Although Texas Red oaks or Spanish oaks are highly suspect of possible intra-graft with live oaks. Texas Red oaks adjacent to infected Live oaks will usually scum to the oak wilt disease with in a years time. This does not conclude that intra-grafting actually took place, the Red oaks could have very well became infected by the presents of the beetle carrying fungal spores and not through intra-root grafting. (See FOOT NOTE below) However, it would be rare to find root grafting between a white and a red oak.
FOOT NOTE: There has been some research of physical root exposure of possible intra-species root grafting where a Live oak and Texas Red oak, roots crossed and grew around each other forming callus tissue. However, it has never been confirmed conclusively that they had actually intra-grafted and shared cambium, xylem, vascular or phloem tissue between the two species.
Intra-species Root Grafting of Oak trees: Red Oak’s roots graft with other Red Oaks. Likewise, Live Oak’s roots graft with other Live Oaks. There has been no evidence that there is intra-species root grafting.
A Cloned Mott of Live Oak Trees
"Sometimes when you are walking through what you think is a grove of Live oak trees, you are really simply walking through a grove of a single individual tree."
The above photos are illustrations of how new Live oak Motts develope. These small Motts are located in open pasture land, where an acorn was deposited onec it germinated and developed roots and ramets, now several small cloned trees are growng off this one root system.
If you stand among of hundreds of Live oaks trees, you're not necessarily in a forest. Biologically speaking, these Motts or groves are actually one tree. It's a clone formed when an individual tree began reproducing itself thousands of years ago. As the Live oak tree sent out its roots, it also sent up new sprouts, called ramets. They look just like individual Live oak seedlings. But the new trees are genetically identical, and they grow from a single root system which is actually parts of one organism.
Live oak trees also produce seeds (acorns). But the trees evolved with the ability to clone themselves in order to overcome the hot, dry, and rocky conditions that make it hard for seeds to sprout. Most trees are very bad parents and do not want to compete with their sybling, they depend of birds and squrrels to distribute the acorns and part of the nathural forest diversity. Also they predispose a fungus to destroy the germination of the acorns that are left under their canope to elminate any further competition.
A dozer with a ripper bar
|Methods of Trenching: Because infected trees can continue to spread fungal spores through their roots for years after they die, severing the root grafts between connected trees is another useful measure; A Bulldozer with a 6 ft ripper bar or vibratory plow can make cuts as deep as 6 feet depending on the type and depth of the soils. Other methods of trenching equipment are illustrated below. It is important to remove and destroy the dead trees and tree roots as the pathogen can remain alive in the root system upto 4 years or until the water content or the roots drops below 38 percent.
(See article Isolation and Trenching http://scenichillsnursery.com/isolation/index.html)
Photos by Jim Rediker
2. The oak wilt fungus can also be carried from tree to tree by insects. Overland transmission happens in spring and the fall, when a "fungal mat" forms under the bark of an infected tree (The Texas Red oak or Spanish oak), causing the bark to break open. While the beetle is feeding on the fruiting fungal mat, they accidentally pick up fungal spores, much the way a bee or hummingbird may accidentally pick up pollen when it sips nectar from a flower. If a beetle dusted with spores is then attracted to another tree that has a fresh wound oozing sweet sap, the spores enter the tree through the wound and the fungus starts to grow. Live oak trees do not produce spore mats, the Red oak is the only tree that produces the inoculum fungal mats.
Another recommended step is cutting down dead trees BEFORE spring arrives, The Texas Red oak or Spanish oak. that dies in late summer or early fall should be removed immediately and burned. Otherwise in the early spring the spore mats form under the bark and break open and attract feeding beetles. After a few months of summer heat, any fungus in the tree will be killed if the tree is not destroyed during the winter. Spore mats do not develop during summer months as temperatures above 95 degrees F. will dry out and destroy any potential fungal mats.
Since oak wilt is native to North America, one question that arises is, why has this disease become so common in recent years?. The disease seems to be intensifying mostly in urbanizing areas--in places where people are buying building lots in wooded settings. As the lots are prepared for homesites when the disease is spread by the beetles, trees are inevitably nicked and damaged by bulldozers or other machinery. Homeowners can urge contractors to protect trees with fencing and otherwise work to minimize the damage to live trees. (See Oak Wilt - How It Was First Controlled)
Oak wilt fungus has been a serious problem for homeowners, because the value of your property goes down when your mature shade trees die. But ecologists say the fungus may actually be a GOOD thing for forest ecosystems. In recent years, the national policy to prevent forest fires may have allowed some stands of oak trees to become TOO dense. When trees die of oak wilt, however, GAPS open in the forest canopy--and these sunny clearings are attractive to wildlife.
Ronald F. Billings Texas Forest Service
Control root grafts. Four factors influence the likelihood of root grafting between two trees: 1) trunk diameter of both trees; 2) distance between trees; 3) soil type and drainage; and 4) tree species. For example, research shows that large (12” diameter) trees growing in sandy soil will likely form grafts if the distance between them is less than 93 feet. However, the same size trees growing in heavier, loamy sand may form root grafts if the distance between trees is less than 74 feet. In other words, roots are likely to spread farther in sandy, rather than heavy soil.
Oaks growing in heavy clay soils that are within 30 to 50 feet of diseased trees are likely root grafted and should be considered as “infected suspects”. This means that they may already be infected but are not yet showing symptoms. As previously mentioned, root grafts are most common between oaks of the same species, also it is necessary to place barriers between a member of the Texas Red oak group and a member of the Live oak group.
Remove dead trees: Diseased, Texas Red oaks and dead oaks should be removed and burned as soon as possible, unless removal would wound surrounding trees. If that is a possibility, remove the diseased or dead oaks in late fall or winter. Since fungal mats are not known to develop within members of the Live oak and white oak group, there is less urgency in removing dead or dying trees that belong to this group. However, remember that all dead shade trees present a landscape hazard and should be removed as soon as possible after death. Pruning tools should be disinfected before trimming another tree or noninfected tissue. To disinfect tools: (1) remove wood fragments; (2) soak for several minutes in a disinfectant such as Consan 20 (one percent solution) or liquid household bleach (diluted 1 to 5 with water), and then (3) rinse the tools in clean water and then spray with WD40.
The application of a herbicide to infected trees to create a chemical safety barrier: It is possible to use some herbicides before removing the tree to kill more of the root system more rapidly than by just cutting the tree. This is done by applying the herbicide to notches cut into the trunk, just deeper than the bark. Do not make the notches (called frills on the herbicide label) too deep. Your objective is to cut to the phloem layer which is just under the bark. The phloem is the tissue in the plant that carries food from the leaves to the roots. This is most effective in the autumn, though it will also work well if done in the summer. It is important that there be leaves producing food which is being translocated to the roots through the phloem. Look for herbicides labeled for this purpose. A few weeks after applying the herbicide the tree may be cut. This practice should be done with great caution as nearby trees of the same species do inter-graft and this treatment can disperse the herbicide to neighboring trees with devastating results. Roots can grow beyond, three time the drip edge depending on the type of soils.
The Draw Back of this Procedure: The intention is to kill the root system of the dying or infected tree root system and stop the spread of oak wilt, which has proved to be a more dangerous practice than a beneficial one. The herbicide applied to the stump or tree as described above, is absorbed into the root system and continues dispersal through the transportation across root grafts as a result of the movement of water to transpiring healthy trees from the non-transpiring stumps. In parts of these root zones, all the oaks are (cloned) grafted together. Under these conditions the herbicide dispersal can enlarge rapidly, and become as deadly as the oak wilt disease itself. This is a practice by unscrupulous, and ill-informed tree services with the intentions for financial gain only, they are in need of very serious scientific council. I would urge the landowner to take legal action against this kind of practice for the belligerent destruction of property. Systemic Herbicide to Kill a Tree and to Control Regrowth.
In some cases it is not possible to install trenches. Researchers and practitioners continue to investigate the use of systemic fungicides in an attempt to provide safe, long-lasting protection against oak wilt. While there are several injectable fungicides labeled for the control of oak wilt, many researchers and practitioners agree that " KESTREL " is currently the most effective. While " propiconazole ''can be applied using the newer "micro-injection capsules", most practitioners prefer the traditional " KESTREL " macro-injection technique.
It becomes necessary to inject high dollar value trees to create a barrier in-order protect other trees and help stop the progression of the disease. The fungicide " KESTREL " can be used to reduce Oak Wilt symptoms; however, this is not a cure. " KESTREL " is labeled for use as preventative and therapeutic injections. Therapeutic injections have the best chance of working if the tree shows less than 10-20% crown loss due to oak wilt. If more than 30% of the canopy is showing symptoms of the disease, the fungicide treatment is not likely to be successful. A therapeutic dosage rate or 20 mils per dia. inch is recommended for any suspect trees or the large trees in close proximity of the disease center. Annual re-treatment of these trees is also recommended, as it takes about three years for a tree to recuperate under perfect conditions. Some trees are just beyond saving at the time of treatment. It is far better to inject trees on a preventive basis rather than wait until your trees become infected and retreat on a bi-annual basis to protect the new growth wood. The drawback to using any of the current fungicides is cost and the potential need for re-treatment in one to two years. Thus, fungicides are suggested only where high value trees are in danger and when all other appropriate control measures, listed above, are used.Tree injections should only be made by trained arborists or others trained in injection techniques and diagnosis of Oak Wilt. However, some of the treated trees in the yard will survive. However, researchers and practitioners tend to agree that it is a waste of money to inject members of the red oak group (Texas Red oak or Spanish oak) that show any symptoms of oak wilt. Oak wilt cannot be controlled by the application of any surface fungal spray, foliar fertilizer or bio-stimulants making pesticidal claims to cure oak wilt, because this disease is internal, as the pathogen must live within a living organism. not external or in the soil. (See article: "TreeLife" Now Cured of Oak Wilt and Dutch Elm Diseases) http:scenichillsnursery.com/greatnews.html