There needs to be a collective conscious awareness and a call to action regarding our oak trees here in the northeastern states. At this time of year, we are heading into the dormant season for trees, and part of the process of that time is fall. As a result, it may be too late to notice the obvious signs of discoloration in leaves on your oak trees, but maybe you’ve seen something suspicious happening to the foliage in your oak trees earlier this summer. If your oak trees’ foliage displayed fall coloring or browning in mid-summer months amid the lush green of other trees, what you have witnessed is a sign called “flagging.” More specifically, if leaves started changing colors from the top of the tree’s crown, working its way down, and if leaves themselves showed signs of changing from the tips and margins moving inward towards the base, that’s the first red flag. If you can remember approximately what time frame the foliage seemed to take this type of turn for the worse, it could be helpful to confirm the diagnosis of which pathogen your oak tree may have. If your oak tree started showing signs of flagging in mid summer (July), unfortunately there’s a chance your oak has been stricken with Oak Wilt.
What is oak wilt?
Oak wilt is the disease that is caused by the pathogen Bretziella (Ceratocystis) fagacearum, a fungus. The fungus makes its way into the water transportation system, also known as the xylem, and disrupts the process. Depending on your species of oak tree, this could mean weeks until the tree succumbs to the disease, or for some species over the course of many years. If your oak tree is of the “red oak” grouping of oak trees, the oaks with pointed tip leaves, this is usually a quick death sentence for the afflicted tree. However, if you have several oaks on your property, there are measures that can be taken to stem the spread of the fungus, and possibly save the rest! If your oak trees have rounded tips for leaves, they belong to the “white oak” grouping, which are much more resistant to the fungus.
How do oak trees get oak wilt fungus?
There are two main ways the fungus that causes oak wilt is spread. First, it can be spread above ground by a vector, which is a carrier of the pathogen. In this case, the vectors are sap sucking beetles that migrate from fungal mats of infected trees to healthy trees and pass the pathogen on through fresh, open wounds. The second way the pathogen is transmitted is underground, through interconnected root systems often shared by oak trees. Having that information is important because it provides us with options to stop or slow the spread of the fungus.
What can be done?
In order to stem the tide of oak wilt from spreading, preventative measures are the most successful measures. One of these measures is that trees can be treated with a systemic anti-fungal. Systemic means a treatment to the inner water transportation system of the tree. This is done by trunk injection, where an anti-fungal is directly injected into the water moving system of the tree through small holes. Should the tree become exposed to the pathogen, it will now contain the fungus killing chemical. This is a great way to prevent the first way an oak tree can get the pathogen, above the ground via vector, but it does little to stop the spread through the root system. To prevent oaks from spreading the fungus via roots, the trenching method of breaking up interconnected roots should be implemented.
If an infected tree is in the area of healthy oaks, the infected tree should be removed, chipped, and stumps grinded and buried. Firewood left on site can contain persistent fungal mats, and stumps as well. Timing is everything, months where the pathogen and vector are less active should be chosen for such activities if the safety of the situation allows. Timing is also important for pruning of oaks. Avoid pruning in the early spring up until mid-summer is best (again, unless there’s an emergency, storm damage, tree failure, etc). Pruning activities should be limited to late summer through fall and winter months, where it seems the hot, dry conditions of late summer limit the spread of spores, while the colder conditions slow the activity of the vector.
Currently, the only way to confirm diagnosis of oak wilt fungal infection is to send leaf samples or fungal mat samples to the lab at Rutgers, but knowing the signs can give your arborist a head start in the preparation to prevent the spread and contraction of this destructive disease by your oak trees. Be proactive, be aware, and get the ball rolling by contacting your arborist today.
