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Control of Chestnut Blight

Some information on the history of trying to control the disease and basic methods of control

Excerpt taken from Volume 7, Issue 1 of the Journal of the American Chestnut Foundation

Blight Control #1: Soil Compress Method.

Some years ago 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.

This is usually accomplished by making a black plastic sleeve to fit around the trunk, securing it with weatherproof tape, and filling it at least 2 inches thick with moist soil. You can add water at the top once or twice if it dries out. Obviously, this will be difficult to carry out when your tree develops cankers in the crown after it gets to be thirty or forty feet tall, but this method is a valuable management tool when appropriate.

More information on mudpacking

Link to an article that first describes the efficacy of the soil compress method in controlling chestnut blight cankers.

Blight control #2: Hypovirulence

Hypovirulence is a condition in which the blight fungus itself gets sick.   What usually causes this weakening of the fungus is actually a virus, which can be spread from one fungus to another. Someday soon hypovirulence may be an easy method to use for saving chestnut trees, but right now there are no commercially available preparations of the virus and you are in the area of experimentation. The researchers who work on this problem are seldom able to find the time to go through the long process of matching virus and fungus types to save a specific tree, but that doesn't mean you can't experiment on your own.  "Wild" hypovirulence, occurring naturally, is becoming easier to find. If you want to get hypovirulence established in your plantings, you might try this: Go into your local woods to someplace where you know there are many surviving chestnut sprouts. Look for bigger sprouts with large, swollen cankers on them. If you find a tree that has been surviving with a canker for several years, you may have found a case of wild hypovirulence.  Since this is the realm of experimentation, expect a lot of failures. Getting the weak strains of fungus transferred to your planting will not be easy. You can try several things, all of which may work -or may lead to worse infections. If you have serious infections in your planting already, you will not have much to lose. The object is to transfer some of the sick fungus, still alive, to a serious canker you want to infect. Try cutting out a small piece of the hypovirulent canker, including as much living bark as possible, and grafting it into the canker you want to heal.  It may help to do this in several places around the edge of the killing canker. If you are lucky, and the two blight cankers are the same type, you may be able to convert a canker that would have killed the stem into one which will only swell up and look bad. In time, if you keep at it, you may be able to establish many hypovirulent cankers in your planting, and it may then start to spread by itself. Or not. There are still many unknowns when dealing with hypovirulence; but there is no doubt it keeps trees alive, and has spread in several places. (See page 14 of TACF Journal Volume 7, Issue 1)

More information on hypovirulence

Blight control #3: Chemical

In most cases we do not think of using chemical fungicides 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, the treatments are expensive, and sometimes don't work longer than one ore a few seasons.

Thanks to Dr. Fred Hebard for the following information on past chemical controls:
(1900-1910s) = Bordeaux mixture and other standard protectant fungicides of the time . 
These are not systemic or curative, but rather prevent new infections on treated parts.  Thus they mostly work against leaf spots and other diseases that depend on huge numbers of lesions to stress the host.  The chestnut blight fungus can get by with one lesion.  Also, the protectants will still let one or two through now and again, so again weren't efficacious. Finally, they only last two weeks or so and one would have to coat the entire aerial surface of the tree, so highly impractical.

(1960s - 1970s) = Systemic fungicides became available in the 60s or 70s. 
Benlate was the first for ascomycetes and Jaynes and Van Alfen pressure injected it into chestnut stems.  They needed almost phytotoxic concentrations for it to be efficacious.  This work was published in Phytopathology, I believe.  John Elkins assayed Benlate concentrations for Gary Griffin and Jay Stipes.  In chestnut, they tried a root drench rather than injection, which harms the stem, eventually.  They could get phytotoxic concentrations in the stem, but it stayed in the xylem and they did not get efficacious concentrations in the phloem (bark) where it would do the most good.  I don't think this work was published

(1990s) Propiconizoles and allies, such as the trademark name, Alamo, show better activity against oak wilt than does Benlate, which suggest strongly that they'd be efficacious against chestnut blight.  Terry Tattar tried some of these against chestnut blight and reported the work in our journal last year or so. He reported good results, using the Maujet system of injection, but this may not eliver enough active ingredient to larger trees for good control.

(Recent) Recent success has been noticed with a Agrifos. Dr. Greg Miller, founding President of TACF's Ohio Chapter, presented information on this chemical at the 2007 TACF Annual Meeting. Here is some more information, posted to the TACF-Growers List by Dr. Paul Sisco:

At the recent TACF meeting in Burlington, VT, Greg Miller of Empire Chestnut Company reported on the use of Agrifos and Pentrabark to treat chestnut blight.  Unfortunately, this treatment only appears to be effective for about 1-2 seasons.  Agrifos 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 being used to treat Phytophthora ramorum in California.  A discussion of phosphorus acid and the various trade names under which it is marketed is at:

http://www.oardc.ohio-state.edu/grapeweb/OGEN/06032005/PhosphorousAcidFungicide_Ellis.pdf

One source of the combined Agrifos and Pentrabark is:  http://www.amazon.com/Agrifos-Pentrabark-Immune-System-Booster/dp/B000J2A02M