The Blight Cryphonectria parasitica

Here are some good places to start your investigation into the chestnut blight (Cryphonectria parasitica)

• Control of Chestnut Blight - some information on the history of trying to control the disease.
• Forest Pathology - Chestnut Blight - a good introduction to pathology and the chestnut blight, maintained by USDA Forest Service Plant Pathologist, James Worrall.
• On the introduction of the chestnut blight - From Dr. Sandra Anagnostakis at the Connecticut Agricultural Experiment Station
• The Life Cycle of Chestnut Blight - a pdf file approximately 150 KB in size
• Chestnut Blight - a powerpoint presentation, ~ 2 MB in size, hosted by the College of Natural Resources at UC Berkeley
• General information on chestnut blight
• Cryphonectria parasitica, cause of chestnut blight - by Tom Volk, Professor of Biology at the University of Wisconsin-La Crosse

Interested in the history of the chestnut blight? Bill Lord, TACF member wrote the following text on "Tracking the Chesntut Blight", an article detailing most prominently the work of plant hunter Frank N. Meyer, his explorations about China during the early 20th Century, and his thoughts on both finding the blight on chestnuts in China and how to possibly control the blight in America.

• Click here for the text of that article (posted with permission)

For more information on the blight as seen first-hand in China, check out Ban Li, which is Chinese for "chestnut". The article below is a partial translation by Chengguo Wang of the Northwestern College of Forestry in Shaanxi. The original Chinese text was drawn up in 1979 for use within Chinese production areas. Only parts of the text were translated.

Right-click here to download the target, a PDF of Ban Li. ~70 KB in size

CONTROL of CHESTNUT BLIGHT

1. Mudpacking
2. Hypovirulence
3. Chemical

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

Blight Control #1: Soil Compress Method. (link to more information on mudpacking)
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.

Blight control #2: Hypovirulence. (more information on 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)

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, and the treatments are likely to be expensive.

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: