It is often the case, when we have found, identified and validated an American chestnut in Connecticut, that the tree has some traces of blight. It can range from barely started to what is certain to cause the imminent demise of the tree. Since we seek out trees that are large and have the potential to flower, these specimens are expected to be among the oldest American chestnut, and therefore to have had the greatest exposure to blight. It goes with the territory to assume some type of biological control will be necessary to help the tree survive until its nuts can be harvested, and we have capture the genes for the next generation. Even then, it is advisable to prolong the life of the mother tree. We have had many circumstances in which we have poor harvest or germination, and having the mother tree available for a subsequent pollination and harvest proves fortuitous.
So you ask what are the options? How do I identify chestnut blight, and what alternatives are available to manage the blight once identified?
Identification
Blight presents itself differently on trees of different age and especially bark morphology. On smooth-barked young trees, such as shown below at left and center, cankers typically are orange in color. The blighted section contrasts heavily with the gray to green color of the uncankered stem. This orange color is especially evident when the bark is wet. Cankers typically will also bear numerous orange fruiting pustules, or stromata, of the blight fungus. The orange color of individual stromata is not clearly depicted in the rough photographs below, but is easily visible to the naked eye in nature. Most of the orange color in the left-hand photograph is due to stromata, and most of the pimply-looking bumps on the canker in the center photograph are stromata.
On older, rough-barked trees, like that in the right-hand photograph, most of the canker will be hidden underneath the bark. Frequently, the only sign of the canker will be orange-colored longitudinal cracks in the bark, as at the arrows. Close examination fof those cracks frequently will reveal rows of orange stromata buried within. A flashlight can facilitate observation of the buried stromata.
Biological Control
There are three forms of biological control potentially available to someone trying to save a tree, or simply exend its life. Timothy McKetchnie wrote an article originally published in January 2006 on Biological Control and you may read it here in its original form. Below we discuss at a high level the three forms of control and provide references where you can pursue further research.
Mudpacking
Many people ask how they can control the blight on a tree that is infected with the blight. One way to extend the life of an infected tree, often for a year or longer, is to apply a mudpack. Dr. Wayne Weidlich, an ACF Director, noted that chestnut blight will grow on chestnut roots if they are exposed. He thought to try packing soil over trunk cankers. It works. Apparently there is something in soil that effectively eliminates the blight fungus and allows the tree to heal. This method is inconvenient to use on very large trees. It will not protect your tree from new infections, nor save a tree that is already girdled, but it can cure individual cankers which might otherwise kill a trunk you want to protect. The basics of the soil compress method are simple: you must keep the blight canker, and the entire trunk all around it at least a foot above and below any signs of blight, covered with moist soil for at least a couple of months.
We have successfully extended the lives of several trees in Connecticut by the process of mud-packing. It should be noted, that late identification of blight, and extremely large areas of blight diminishes the possible success of mudpacking. We have had several large trees documented as having advanced blight that we simply haven't been successful in protecting. On the other hand, we have had several situations where we have applied mudpacks and had a tree survive to harvest. Mudpacking has been studied fairly extensively, and is recommended as a biological control approach by many plant pathologists. by Dr. Sandra Anagnostakis of the Connecticut Agricultural Experiment Station, by TACF Staff Pathologist Dr. Fred Hebard in this document at the Massachusetts Chapter web-site.
Hypovirulence
Hypovirulence is a condition in which a virus infects the blight fungus. The tree is able to effectively build callus around the weakened fungus and effectively survives the infection. There are challenges with hypovirulence which Timothy McKetchnie reviews in his publication. There is an excellent article on hypovirulence on the Vircgina TACF Chapter web-site.
Chemical Control (Fungicides)
Recently there has been talk of using chemical fungicides such as Agri-Fos and Pentra-Bark to control chestnut blight. Chemicals would be useless in a forest situation, but they can be used if there are one or two trees you particularly want to keep alive. You may have seen elm trees being injected with chemicals to keep them from dying of Dutch Elm disease. The same method can work on American chestnuts. If this is something you want to do, hire a professional tree service to handle the injections. The chemicals used are powerful. It is quite possibly illegal in your area for unlicensed persons to use them. Trees protected chemically have to be re-treated every year, and the treatments are likely to be expensive.
Agri-fos is phosphorous acid, and it is marketed under other trade names, such as Aliette. Pentrabark is a surfactant to help move the acid through the bark into the vascular tissue of the tree so that it can be transported systemically. The combination of Agrifos and Pentrabark is also being used to treat Phytophthora ramorum in California. Discussions with the CT Agricultural Experiment Station have indicated that from a pathological perspective, these chemicals should not work with cryphonectria (blight) species. Here is a discussion of phosphorous acid and the various trade names under which it is marketed.
