American chestnut tree blight

The American Chestnut Tree

The American chestnut tree (Castanea dentata) is a large, monoecious deciduous tree of the beech family native to eastern North America. Before the species was devastated by the chestnut blight, a fungal disease, it was one of the most important forest trees throughout its range, and it was considered the finest chestnut tree in the world.

The American chestnut was an essential component of the eastern U.S. forest ecosystem. These “Mighty Giants” stood up to 100 feet tall and numbered in the billions. As a late flowering, reliable, and extremely productive tree, the American chestnut was unaffected by seasonal frosts, making it the single most important food source for a wide variety of wildlife.

Rural communities depended upon the tree’s annual nut harvest as a cash crop to feed livestock. The chestnut lumber industry was a major sector of rural economies. Chestnut wood is straight-grained and easily worked, lightweight and highly rot-resistant, making it ideal for fence posts, railroad ties, barn beams and home construction, as well as for fine furniture and musical instruments.

At the beginning of the 20th century, the fungal pathogen responsible for chestnut blight (Cryphonectria parasitica) was accidentally imported into the U.S. from Asia. It was first detected in New York in 1904, spreading rapidly throughout the eastern forests. As a wound pathogen, the fungus enters the tree through an injury in the bark. It spreads to the underlying vascular cambium and wood, killing these tissues as it advances. The flow of nutrients is eventually choked off to and from sections of the tree above the infection, killing the tree above ground. By 1950, the fungus had eliminated the American chestnut as a mature forest tree.

Helping American chestnut trees recover from blight | Opinion

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“Chestnuts roasting on an open fire” is an American tradition, but the tradition actually dates back to prehistoric times. Roasting chestnuts is a big part of Italian holidays, and chestnuts are an important food crop in Asia and southern Europe.

The chestnuts we roast these days don’t come from our native American chestnut trees that once numbered in the billions and dominated forests throughout the eastern United States. Today our roasted chestnuts are Asian varieties.

For thousands of years, the native American chestnut (Castanea dentata) was one of the most important forest trees. Each fall, the tree’s sweet nuts would blanket forest floors, providing a bounty for critters and humans alike. Strong, rot-resistant chestnut wood was a prized building material.

But in the late 1800s, a bark fungus was accidentally introduced into North America on imported Asiatic chestnut trees. American chestnuts had little resistance, and the resulting blight – first discovered in 1904 in New York City – quickly spread.

Within 50 to 60 years, three to four billion American chestnut trees died. Although a small percentage of American chestnut trees survived the blight, the great chestnut forests that had existed for millennia were gone.

“The blight was one of the first ecological tragedies to hit this continent,” said Rex Parker, a member of the Hopewell Township Environmental Commission, which is leading an effort to restore American chestnuts in Central Jersey.

The Hopewell Environmental Commission has teamed up with the American Chestnut Foundation and several New Jersey nonprofits to plant new chestnut trees on public land.

Last spring, Hopewell Township and the Friends of Hopewell Valley Open Space planted 170 specially chosen nuts in protective tubes within a deer-fenced section of the Fiddlers Creek Preserve.

A dozen American chestnut seedlings were planted at the township’s Woolsey Park, and more were planted at nearby preserves in partnership with the D&R Greenway Land Trust, The Watershed Institute and Sourlands Conservancy. Hopewell Environmental Commission member Mike Aucott initiated the chestnut planting project and directed the plantings.

The Hopewell Township plantings are the latest of several efforts across this state we’re in to grow chestnut trees – either from native American chestnuts with natural blight immunity, or hybrids created by breeding American chestnuts with Asian varieties.

Among the previous plantings were experimental plots on Schooley’s Mountain in Morris County, in Basking Ridge in Somerset County and in Tenafly, Bergen County.

According to Stephen Hoy of the American Chestnut Foundation, work is continuing on a long-term project to create the best hybrid chestnut with the natural characteristics of American chestnuts and the blight resistance of Asian varieties.

The effort started in 1983 with the idea that six generations of chestnut trees would be needed to create the best genetic lines. Currently, the fifth generation is being grown on a 10-acre orchard at Penn State University.

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Hoy, who runs the orchard, said young trees are tested for blight resistance by inoculating them with the fungus. Those that survive two rounds of fungus – first a small amount, then a much larger amount the following year – are allowed to mature and are bred with other survivors.

Whenever possible, said Hoy, the Chestnut Foundation will also breed trees in the orchard with wild trees that survived the blight. From time to time, he noted, hikers discover mature American chestnut trees previously unknown to the foundation.

“We have materials on our website that tell people what to look for,” said Hoy. “If they come across a tree that may be an American chestnut, we ask them to record the longitude and latitude and send us a leaf and twig sample.”

Additional hope for American chestnuts may come from gene splicing. Scientists at the State University of New York (SUNY) in Syracuse are experimenting with splicing DNA from wheat into the DNA of chestnut trees to introduce an enzyme that provides resistance to the blight fungus. But regulatory approval from the federal government will be needed to distribute these “transgenic” chestnut trees outside SUNY.

With scientific advances and a bit of luck, someday our forests may again be filled with mighty American chestnut trees!

Michele S. Byers is executive director of the New Jersey Conservation Foundation.

About chestnut blight

Chestnut blight is a disease caused by a bark-inhabiting fungus (Cryphonectria parasitica), which mostly affects the trunk and branches of host chestnut trees.

The disease invades stems and branches of any size and causes cankers that can grow rapidly. Cankers are dead or malformed areas of bark or woody tissue. In most cases cankers continue to develop until they surround the trunks, stems or branches and the tree eventually dies. Other symptoms of chestnut blight include cracking or peeling bark, trunk and branch swelling, bark and wood degeneration or death, and additional resin exudates.

Under favourable environmental conditions, orange fruiting bodies (stroma) are produced on the outside of the bark inside the canker margins. Spores are formed in stroma, which can spread the disease.

The disease has the potential to spread from cuttings and dead wood for up to nine months.

Orange stroma (2-3mm diameter) visible on the bark of stems and branchesCankers and bark splitting on stems and branches

How does chestnut blight spread?

Chestnut blight can spread via:

  • Airborne spores
  • Rain splash
  • Transport of infected material
  • Farm operations e.g. pruning
  • Machinery and equipment.

Chestnut blight can also be spread through budding material and cuttings taken from infected trees.

It can also be spread by two types of spores produced in the orange stroma of the fungus:

  • One type of spore is ejected from stroma on infected wood and spread by air movement.
  • The other spore type is released from infected wood onto the tree surface from where it can be spread by rain splash, water, or any object that comes into contact with it (e.g. clothing, tools or equipment).

Cut branches with the disease are also a serious spreading risk, as the fungus grows more rapidly on dead wood and can produce spores for up to a year after cutting.

Chestnut blight has also been transferred to healthy trees by the use of contaminated cutting equipment such as saws, knives and chainsaws, or tree injection equipment.

Chestnut blight may lie dormant and symptoms may take over a year to develop so, as a precaution, it is important to keep monitoring trees for symptoms.

Can chestnut blight be stopped from spreading?

The best option for containing the disease is to eliminate any sources of infection, including spores of the fungus. This means that infected limbs and tree trunks must be cut off and burnt on site.

New infections cannot be seen until they fully develop and spread onto the bark, so infected tree parts may be missed in an initial pruning. Therefore, pruned trees should be regularly monitored for a reappearance of the disease.

Any destruction and disposal of infected trees must be done under Agriculture Victoria supervision to ensure the highest biosecurity levels of farm hygiene and decontamination are observed.

Is it safe to receive chestnut trees or propagating material?

Chestnut blight is most readily spread through the movement of infected budwood or cuttings. Do not receive any cuttings or new trees unless the source material is from a grove or nursery outside the Restricted Area (see Market access information and material movement restrictions), or from a trusted source within the Restricted Area that has been surveyed and found to be free of the disease.

There are restrictions in place in the Ovens Valley regarding chestnut and oak plant movement. Heavier restrictions are in place in a small area of Eurobin, including machinery and equipment that is used on or been in contact with chestnut or oak trees. Penalties are in place for non-compliance with these restrictions. See Market access information and movement restrictions for further information.

Control of Chestnut Blight

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

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:

Chestnut Blight


The fungal pathogen, Cryphonectria parasitica,
that causes Chestnut blight

Chestnut blight (Cryphonectria parasitica)
The Cause of the Problem


Canker of Chestnut blight that has encircled and killed an American chestnut tree

  • The Chestnut blight fungus (Cryphonectria parasitica; formerly known as Endothia parasitica) was likely introduced to North America on nursery stock from Asia and was first observed killing trees in the Bronx Zoo (New York City) in 1904. From there, Chestnut blight spread rapidly through eastern North America, and across the entire natural range of the Chestnut. It reached southern Ontario in the early 1920s; and by the 1930s almost all American chestnut trees were infected and dying. By 1950, this once prevalent tree species of the eastern forests was reduced to the status of a threatened species.
  • However, American chestnut has a great regenerative capacity. Chestnut blight only infects the above-ground parts of trees, causing cankers that enlarge, girdle and kill branches and trunks. The surviving root systems can regenerate to produce sprouts that grow into small trees. These sprouts become infected and die but sometimes a few nuts are produced first. Today, this sprouting and infection cycle continues across the original range of American chestnut.

  • Canker of Chestnut blight. The orange-coloured areas at the edge of the canker are where Chestnut blight is actively growing and sporulating.

    Of the three best known chestnut species, the American Chestnut (Castanea dentata) is the most susceptible to chestnut blight, and the Chinese chestnut (C. mollissima) is the most resistant. The European chestnut (C. sativa) is intermediate in resistance.

  • Early attempts at controlling Chestnut blight involved crossing with the Chinese chestnut, with the expectation that some of the hybrids would show resistance as well as the upright form of the American chestnut. However, the results were discouraging. Recently, a new program involving several generations of backcrosses to the American chestnut was initiated in another attempt to combine resistance with good tree form. A strong program using tried-and-proven resistance-breeding methods is currently underway at several research centres in the USA .
  • Scientists are also evaluating biological control for the management of chestnut blight. Some strains of the Chestnut blight fungus are infected with a virus which reduces the virulence of the fungus, so that an infected tree is able to produce callus, overgrow the cankers, and survive. This form of biological control occurs naturally in Europe and has allowed European chestnut to re-establish there. However, this method has not been as effective in North America and scientists are trying to determine why (see Hypovirulence).
  • It is worthwhile to note the blight pathogen that virtually destroyed the American Chestnut in the nineteen hundreds is still present and active in the environment today. The blight continues to kill both longer living chestnuts and newer regentative sprouts. It is not likely that the pathogen will be stopped but it is hoped that a blight-resistant American Chestnut can occur and thrive in our natural ecosystems.

History of the American Chestnut

The history of The American Chestnut Foundation (TACF) chronicles the ongoing pursuit of a fundamental goal: to develop a blight-resistant American chestnut tree through scientific research and breeding, and to restore the tree to its native forests along the eastern United States.

More than a century ago, nearly four billion American chestnut trees were growing in the eastern U.S. They were among the largest, tallest, and fastest-growing trees. The wood was rot-resistant, straight-grained, and suitable for furniture, fencing, and building. The nuts fed billions of wildlife, people and their livestock. It was almost a perfect tree, that is, until a blight fungus killed it more than a century ago. The chestnut blight has been called the greatest ecological disaster to strike the world’s forests in all of history.

The American chestnut tree survived all adversaries for 40 million years, then disappeared within 40.

The American chestnut tree (Castanea dentata) once dominated the eastern half of the U.S. Because it could grow rapidly and attain huge sizes, the tree was often the outstanding visual feature in both urban and rural landscapes. The wood was used wherever strength and rot-resistance was needed.

In colonial America, chestnut was a preferred species for log cabins, especially the bottom rot-prone foundation logs. Later posts, poles, flooring, and railroad ties were all made from chestnut lumber.

The edible nut was also a significant contributor to the rural economy. Hogs and cattle were often fattened for market by allowing them to forage in chestnut-dominated forests. Chestnut ripening coincided with the holiday season, and turn-of-the-century newspaper articles often showed train cars overflowing with chestnuts rolling into major cities to be sold fresh or roasted. The American chestnut was truly a heritage tree.

All of this began to change at or slightly before the turn of the century with the introduction of Cryphonectria parasitica, the causal agent of chestnut blight. This disease reduced the American chestnut from its position as the dominant tree species in the eastern forest ecosystem to little more than an early-succession-stage shrub. There has been essentially no chestnut lumber sold in the U.S. for decades, and the bulk of the annual 20-million-pound nut crop now comes from introduced chestnut species or imported nuts.

Despite its decimation as a lumber and nut-crop species, the American chestnut has not gone extinct. It is considered functionally extinct because the blight fungus does not kill the tree’s root system underground. The American chestnut has survived by sending up stump sprouts that grow vigorously in logged or otherwise disturbed sites, but inevitably succumb to the blight and die back to the ground.

American Forests

over the top.”

These restoration chestnuts at Meadowview Research Farm show resistance to the blight. (Credit: American Chestnut Foundation)

At the University of Maryland’s Biotechnology Center in Shadyside, virologist Donald Nuss has been dissecting the American strains of hypovirulence, trying to understand why they don’t spread as easily in the wild here as they do in Europe.

His funding comes from the National Institutes of Health, which is interested in how viruses work; the chestnut hypovirulence is one of the easiest ways to study this, Nuss says.

Nuss has cloned the hypovirulence and inserted it into a transgenic chestnut blight whose effects on trees are far less severe. So far, neither the hypovirulence or his transgenic blight seem able to spread efficiently on their own in the wild, which would be essential for becoming effective across the landscape.

Scientists think the problems lie partly in the large number of strains in which both blight and hypovirulence occur. There is a lot of incompatibility, which retards spreading; also, European chestnuts probably have a little more natural resistance than American chestnuts, which allows the hypoviruses to work more easily there.

The hypovirus here may make the blight too weak, so that it can’t spread in a less destructive form; in effect, vaccinating the chestnuts it encounters against the full-strength blight. Meanwhile, the original blight is able to remain dormant in dozens of non-chestnut tree species, from which it respreads by wind and by birds.

Another hope lies with engineering a transgenic chestnut. A chestnut with a disease-resistant wheat gene has already been produced experimentally by researchers William Powell and Charles Maynard at the State University of New York’s Environmental Science and Forestry school in Syracuse.

Powell says a $5.6-million project that includes sequencing all the genes in the chestnut is two years from completion. He expects that this will allow researchers to produce a chestnut that is pure American except for the addition of a few genes from the Chinese chestnut that confer disease-resistance.

One of the funders of that project is Duke Energy, which is interested in the chestnut’s potential to reclaim coal-mining land, but also in its promise for sequestering carbon dioxide. A Purdue University study shows that the growth rate, size and longevity of chestnuts let them store more carbon, and at a faster rate, than any other hardwood.

There’s also an ancient chestnut tree that Fred Hebard directs you to on your route home from Meadowview. The “Amherst tree” is so large, so gnarled with age, and so rare that, like a few dozen other long-surviving chestnuts, it has been named.

To develop resistance to the blight, young trees are inoculated with samples of the chestnut blight fungus. (Credit: American Chestnut Foundation)

It sits alone in the middle of a pasture near Amherst, Virginia, full of healed-over cankers, its crown wracked by storms, but enduring. Gary Griffin, Hebard’s PhD mentor at Virginia Tech, says these most ancient survivor trees almost all share a few characteristics. “They have some natural resistance, they are infected by the hypovirulence, and they have very good growing environments.”

Griffin, an emeritus professor of plant pathology, has been working since 1973 grafting tissue from old survivors (and younger ones that have made it to about 15 inches in diameter) onto American chestnut rootstock, crossing these to one another. There is plenty of evidence that genetic resistance to disease can be recovered by crossing even trees with relatively low resistance; but it is taking awhile — “We’re about halfway there,” he ventures.

Griffin has one tree, grafted in the early 1980s, that is now 24 inches in diameter and close to 70 feet tall. “I have no problem with what Fred is doing trying to produce a hybrid,” he says, “but a lot of people also just want to bring back the pure American tree.”

Just as the chestnut blight appears here to stay, so does the movement to restore the chestnut to its place in the forest. In Carroll County, Maryland, in partnership with the American Chestnut Foundation and American Forests, more than 18,000 school children each year participate in a science curriculum built around experimental chestnut orchards.

Nor has the chestnut itself ever really gone away, notes Essie Burnworth, head of the ACF’s Maryland chapter: “There are millions of them around, sprouting from old stumps, sitting as seedlings in the forest understory, just waiting for light to grow.”

Burnworth explains that American chestnuts have an extraordinary ability to “release,” or spurt toward the light when surrounding canopy trees die. Fred Hebard says he’s seen understory chestnuts only an inch in diameter that show 60 years of growth rings, followed by growth that approaches an inch a year after they get access to light.

Chestnut hybrids, grown at the Hashawa Environmental Center in Carroll County, MD. (Credit: Melissa Boyle)

A project to spot chestnuts sprouting within sight of the Appalachian Trail has so far turned up more than 40,000, Burnworth says. Many clear-cuts literally explode with long-suppressed chestnuts racing for the light.

All evidence is that if the blight can be overcome, the chestnut can outcompete most any other hardwood to become part of the forest canopy. “Maybe only yellow poplar, on excellent yellow poplar sites, might outgrow it,” says Kim Steiner.

Fred Paillet, a University of Arkansas geoscientist who often writes on chestnuts, has taken the long view. He cites pollen profiles from North American lakes that show virtually all hemlocks simply vanished from the forests some 5,000 years ago — probably of a disease still unknown — and then reappeared throughout their range a few centuries later.

“The American chestnut, considering it’s been around millions of years, can in the long term probably take care of itself as long as wild woodlands and rodents and jays exist to forage and spread the nuts.” Paillet wonders whether it’s possible for the chestnut to someday be seen as virtually “invasive;” a problem, he writes, “I would gladly live with.”

— Tom Horton writes from Maryland’s Eastern Shore

This article was published in the Winter 2010 issue of American Forests magazine.

Chestnuts: Growing the American Chestnut Tree

Chestnut blight kills only the aboveground portion of chestnut trees, so infected trees that are killed back to the ground resprout only to become infected again, keeping the fungus active. Unless some naturally blight-resistant American chestnut trees are found hidden in an eastern forest (many people have been looking), native chestnuts would grow into timber-size specimens with good edible nuts only in areas in the Midwest and West that have been shielded from the spread of chestnut blight.

It can be difficult to know whether the infective agent is present in your area. Because it can take 10 years or longer for a tree to develop blight symptoms, it’s a gamble to plant American chestnut trees, even in the Midwest and West.

In Europe, the chestnut blight organism has been controlled by infecting the organism with a virus that weakens it so that trees can better resist it.

Harvesting Chestnuts

For better and for worse, chestnuts come inside prickly burrs, each more or less the size of a tennis ball (depending on the variety and the growing conditions) and housing one to three nuts. The “for better” part is that those spiny burrs usually keep squirrels at bay. The “for worse” part is that we humans also have to deal with the burrs.

When chestnuts are ripe, burrs either drop to the ground, nuts within, or open to release the nuts and then drop themselves. Either way, you end up with the ground full of spiny burrs, so shoes are a must when walking under chestnut trees. Squirrels will gather nuts that have been released from burrs, so I pick ripe nuts and fallen, full burrs from the ground every day or two. I help things along by knocking loose burrs off branches with a pole, or by shaking whole limbs. Don’t stand beneath shaking limbs or you’ll be bopped by spiny orbs! Unopened, dropped burrs will mature and open at cool temperatures with high humidity. After you remove the nuts, you can use the burrs as mulch in areas where you want to deter squirrels, raccoons, and other tender-footed pests.

Post-harvest Necessities

The easiest part of growing chestnuts is growing the trees and harvesting the nuts. More deliberate attention is needed to get those nuts into condition for eating. You need three things: avoidance of chestnut weevils, correct curing, and suitable storage. The first step is to mow beneath the trees to make finding dropped nuts easier.

Chestnut weevils lay eggs in burrs in mid to late summer and are common throughout North America. The larvae hatch, eat, then exit the nuts after they drop. The weevils overwinter for one to three years in the soil before emerging and laying eggs again. Tiny holes in chestnut shells are the goodbye wave of the weevil.

My goals are to limit weevil population buildup and keep in edible condition those nuts in which weevils have laid eggs. I reduce the weevil population by picking up fallen nuts daily (or at least every other day) to prevent weevils in infested nuts from entering the soil. Letting chickens or guinea hens forage beneath trees also helps keep weevil populations in check.

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Killing insect eggs or small larvae already within nuts keeps the nuts in edible condition. To do this, put the nuts (after they have been removed from their burrs) in water held at 120 degrees for 20 minutes. Immediately after their water bath, dry the nuts in the sun between wire mesh screens, or somewhere outside that is safe from squirrels.

When the nuts are dry, refrigerate them, or store them in a dry, cool spot (less than 40 degrees). Chestnuts are unique among nuts in that their nutmeat is high in carbohydrates, rather than high in oil. The nuts are rather bland at harvest, but after a few days in the refrigerator, some of the starches change to flavorful sugars.

For long-term storage of nuts, avoid both mold and excessive drying. Mold will render nuts inedible, while excessive drying hardens them. Hardened nuts are still edible and can be ground into flour or reconstituted by soaking or cooking in water. Ideal storage conditions are temperatures just above freezing with high humidity, such as in dry peat moss or sawdust in a closed plastic bag that’s then put in a refrigerator or cold root cellar.

I’ve had success keeping chestnuts in wooden boxes at near-freezing temperatures in the garage. My favorite way to prepare them is to make a slit along one side of the shells, roast them, peel off the shells and eat the nuts while still warm. Roast chestnuts in an oven or toaster oven at 400 degrees for about 30 minutes, or in a pan over a woodstove or fire.

Choosing a Chestnut Species

The most common edible chestnut species are the American chestnut (Castanea dentata), Chinese chestnut (C. mollissima), Japanese chestnut (C. crenata) and European chestnut (C. sativa).

Chinese chestnuts are generally hardy to Zone 5, but some are hardy to Zone 3. European and Japanese species are hardy to Zone 5, and American chestnuts are hardy to Zone 3. Chinese chestnuts are the most blight-resistant, the Japanese chestnut is slightly resistant, and the two others are more susceptible to blight. At the extremes in tree structure are the American chestnut, which is tall and upright, and the Chinese chestnut, which has wide-spreading branches.

The nuts of different species are equally variable. American chestnuts are small, have an easily removable pellicle (the thin brown skin around the nutmeat), and are the sweetest of the edible chestnuts. European species have a variable, usually mild flavor, and Japanese chestnuts are sometimes bitter. Chinese chestnuts have a smooth, subtly sweet flavor.

Good flavor, growth habit, and blight resistance all make a strong case for planting Chinese chestnuts or their hybrids. In fact, many chestnut varieties are hybrids representing two or more species, and tree form and size will, to some degree, reflect that parentage.

Great Chestnut Varieties

Colossal: This European/Japanese hybrid has an upright habit and produces large nuts. It is moderately susceptible to blight.

Dunstan Hybrid: This variety is a hybrid of American and Chinese chestnuts. Seedling trees with an upright growth habit consistently bear medium to large, sweet nuts.

Eaton: Likely a seedling of ‘Sleeping Giant’ (a hybrid of American, Chinese and Japanese chestnuts), ‘Eaton’ has a spreading habit with ornamental, glossy leaves. It produces medium to large nuts that ripen early. Nuts have terrific flavor and sweetness and store well, but can be small if conditions aren’t ideal (too wet, too dry or poor soil).

Mossberg: A Chinese variety with large nuts that peel well.

Qing: Pronounced “ching,” this pure Chinese species (the original tree was planted in western Kentucky with Chinese seed) has a spreading habit and ripens midseason. ‘Qing’ produces large, shiny, medium- to dark-mahogany nuts. Nuts are easy to peel, have an excellent, sweet flavor, and an excellent keeping quality (three to four months). ‘Qing’ is a heavy producer, and can actually set too many nuts, which causes reduced nut size. Note: Delayed graft failure, in which the graft seems to be successful but breaks off after a few years, can be a problem with this variety.

Peach: This pure Chinese variety has an upright habit and ripens midseason. It yields medium to large nuts with a slight (edible) peach fuzz on them.

Chestnut Resources

CHESTNUT TREE SOURCES

Burnt Ridge Nursery
Chestnut Hill Tree Farm
Empire Chestnut Co.
Nolin River Nut Tree Nursery

MORE CHESTNUT INFORMATION

The American Chestnut Foundation
Chestnut Growers of America
Northern Nut Growers Association

Lee Reich holds a doctorate in horticulture. His most recent books are Landscaping with Fruit and The Pruning Book.

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