To Control Oak Wilt Disease
Why and When Injection Works
To understand why and when injection works, you need to understand how the Oak wilt fungus gets into and kills oaks. The fungus infects the vascular tissue, causing the vessels in the active, outer rings of xylem to become clogged (as likened to cloistral in humans). The fungus gets into an uninfected oak in one of two ways: either through roots grafted to a diseased tree, or by the bark beetles feeding in the branches or upper crown of the tree. When an oak becomes infected through root grafts, the fungus can spread very rapidly and extensively throughout the tree’s vascular transport system. Injection of currently available fungicides is not effective in protecting trees from root graft infection, or in therapeutically treating trees that have become infected through root grafts. Injection can be effective in preventing or treating infection caused by bark beetle inoculation.
When a beetle that is contaminated with oak wilt fungus spores feeds on a healthy oaks, several factors determine whether the tree will become infected by the fungus, or if infected, or die. These factors include the inoculum load and point of introduction, the aggressiveness of the pathogen, the physiology of the tree, the suitability of the environment for fungal growth (temperature, humidity, soil moisture, chemistry, time of year, etc.), and the ability of the tree to compartmentalize the infection, and the general health of the tree. Injection of fungicide into trees can be effective by either making the infection court unsuitable, or by stopping fungal growth within the tree. The former is the basis of preventive fungicide injection; the latter is the basis of therapeutic injection.
To be effective in preventing infection, a fungicide must inhibit or kill the fungus, and it must be present in adequate concentration at all potential points of infection. Even when injected at fairly high dosages, the quantity of chemical present at the points of potential introduction of the fungus is quite low. The chemical, dosage and means of application are critical to success.
For therapeutic treatment, the fungicide must be applied before the fungus has caused extensive damage to the vascular system of the tree, so early detection and timely treatment are critical to success
The triazole fungicide propiconazole is effective in management of oak wilt disease, It is a highly systemic sterol inhibitor that prevents fungal growth by interfering with cell wall formation. The commercially available formulation of propiconazole (Kestrel®, Quali Pro®, and Alamo®) is microencapsulated to make it soluble in any clean water near neutral pH. has demonstrated propiconazole to be effective in preventing infection following challenge inoculations by the fungus. The rates of propiconazole used is, 10 mils per tree DBH. The current highest label rate is equivalent to 20 mils per tree DBH. Propiconazole at the label rates may provide protection for multiple seasons.
A Bit About Injection Methods
There are two common ways of injecting the available fungicides into the vascular system. Microinjection is forceful injection of a low volume of concentrated chemical into holes drilled into the trunk stem above the trunk root flare or base of the tree. Macro injection is the injection (under pressure) or infusion (with low pressure) of large volumes of dilute chemical solutions into holes drilled in the Trunk flare or base of the tree below soil level.
The macro injection system for injection into the excavated trunk root flare of trees, the circumference of the base is greater and more injection holes could be well-spaced around the base, resulting in greater chemical volume uptake for distribution to the crown of the tree.
The wood tissue in the trunk-flare of this transitional area seemed functionally different from stem tissue, and drill wounds in stem area closed more rapidly with less wet wood or pathogenic infections problems than wounds lower on the trunk root flare.
However, there are some drawbacks to macro injection: injection wounds, if repeatedly inflicted, may eventually result in significant discoloration and decay. The chemicals may also damage the cambium around the injection site. The chemical may also cause foliar phytotoxity, especially on smaller diameter trees. It is most important to follow the dosages recommended on the manufacture's label.
Microinjection for treatment is accomplished with the Chemjet® tree injector syringe. Generally, the tips of the nozzles are placed into 11/64" holes drilled into the trunk stem above the trunk root flare of the tree. The product is first drawn into the barrel of the syringe and locked, once placed
in the tree, it is unlocked by a 1/4 turn and the 23 lb force spring slowly injects the chemical within 3-5 hours The Chemjet® injectors are reusable for more that 1000 times.
Propiconazole, a systemic fungicide, ( XMS .. Xylem Mobile Systemic ) does not require high dilution rates with water, so treatment is considerably faster, and there is less tissue injury at the injection site as it has a near neutral pH factor." It is most important to treat your trees as a preventative application than as a curative application. Once a tree becomes infected is near impossible to save your tree. Literature search revealed that microinjection provides the same or better than adequate distribution and effective concentrations of the chemical to consistently prevent or arrest infections. Microinjection has the same disadvantages as macro injection in regards to phytotoxicity and injection wounds.
Therapeutic treatment is only an option for early stages of infection, but it is a potentially powerful tool when added to successful suppression programs that pivot around thorough inspections and trenching. It is not always effective, but a success rate as low as 50% may be more than enough to justify the cost of the effort. The cost of tree removal is high, and the value of large majestic oaks is even greater.
There are risks to tree health in injecting trees. A long-term preventive injection program may cause significant stem damage to a valuable oak tree. Consider whether early detection (and thus opportunity for treatment) is likely for a high value Oak Trees. As with any resource management decision, it is important to weigh the risks against the benefits.
The Advantage and Convenience of this new Chemjet® Injector Treatment.
The injection holes are small and seal quickly. Like the macro injection, the Chemjet® Tree Injectors, delivers the same prescribed volume of the fungicide, but in a higher concentration, using the tree's natural transport system and the water within the tree for dilution and distribute throughout the entire tree to the areas where its most effective. The application procedure is relatively rapid and far less labor intensive. A 30 " diameter tree can be treated in approximately 15 minutes, and the treatment as like the macro injection is best performed every 2 years for continued and on going protection. Both method of macro and micro-injection have demonstrated to thoroughly distribute chemical in the crown.
There is an art and a science to properly injecting chemicals. The procedure should be done by a arborist or skilled tree care specialist who has been specifically trained in the procedure.
CHEMJET® - Oak Wilt Injection: http://www.oakwilt.com/oakwilt_chemjet_app.html
THE FUNGICIDE KESTREL- How does it work? http://www.oakwilt.com/oakwilt_fungicide_app.html