Chestnut

The fungus (Cryphonectria parasitica) that destroyed the American chestnut as a forest tree, killing an estimated three to four billion trees after arriving on imported nursery stock around 1904. It enters through wounds in the bark, grows in the living tissue, and forms a canker that expands until it girdles the stem - everything above the canker then wilts and dies while the roots stay alive and send up new sprouts, which get infected in their turn. Spores travel on wind, rain, insects, birds and pruning tools. The fungus is now endemic across the entire former range of the native tree, which is why species choice matters so much: Chinese chestnut and its hybrids tolerate infection and wall it off, while American and most European varieties do not.

Watch for: Sunken or swollen orange-brown to cinnamon patches on the bark, often cracked, sometimes with fine orange pimples on the surface. A branch whose leaves suddenly wilt, turn brown and hang on rather than dropping - then trace down the stem to find the canker below it. Fans of buff-colored fungal tissue under bark peeled back at the canker edge. Vigorous sprouting from the trunk or base below a dying top, which is the tree responding to being girdled.

Prevent: Plant blight-resistant stock: Chinese chestnut (C. mollissima) or American-Chinese hybrids such as the Dunstan types, especially anywhere in the former range of the American chestnut. Avoid the large European x Japanese varieties like Colossal east of the Rockies. Then minimize wounds, since the fungus needs one to get in: prune only in dry weather in late winter, keep mowers and trimmers away from the trunk, and cage against deer antler rubbing and rodent chewing. Disinfect pruning tools between trees. Keep trees unstressed - drought-stressed and poorly sited trees wall off infections less effectively.

Treat: There is no spray cure. Cut infected limbs out well below the visible canker, into clean wood, and burn or bin the prunings rather than leaving them under the tree. On a resistant Chinese or hybrid tree, cankers are commonly contained by the tree itself and the job is monitoring and pruning. On a susceptible tree the top is eventually lost whatever you do; the roots usually survive and resprout. Hypovirulence treatment - deliberately introducing a virus that weakens the fungus - is used in research and by some restoration groups but is not a practical home remedy.

The reason this catalog entry is about Chinese and hybrid chestnuts rather than the native tree. On a resistant tree, treat blight as an annual winter inspection job, not a catastrophe.

Two long-snouted weevils (Curculio species) are the main insect pest of home chestnut crops. The adult drills through the developing burr and lays eggs inside the nut; the grub eats the kernel and then chews its way out after the nut has fallen, leaving a neat round hole and burrowing into the soil to pupate. Infested nuts often look perfect when gathered and reveal themselves in the kitchen or in storage a week later, which is why sorting and prompt refrigeration matter so much. Populations build year on year in an orchard where fallen nuts and burrs are left on the ground.

Watch for: Neat round exit holes about the size of a pencil lead in the shells, usually appearing days after harvest rather than at gathering time. Cream-colored, legless, C-shaped grubs inside cracked nuts. Nuts that float in the water test. Fine frass in a storage container. Adults - small weevils with a very long curved snout - on the burrs in late summer.

Prevent: Sanitation is the whole game. Gather nuts daily so grubs have no chance to exit into your soil, and clear every fallen burr and leftover nut at the end of the season rather than leaving them under the tree. Float-test every batch and discard the floaters. Then break the cycle in storage: refrigerating the crop promptly stops the grubs developing, and a brief hot-water dip (about 120°F for 20 minutes) before drying and refrigerating is the traditional home treatment.

Treat: Nothing rescues an infested nut - discard it, and do not compost it where the grub can reach soil. Because the larvae spend most of the year in the ground beneath the tree, keeping the ground clean and disturbed is the practical control; poultry ranging under the trees are genuinely effective at reducing populations. Insecticide programs exist for commercial orchards but are rarely worth it in a home planting where daily gathering and cold storage do most of the work.

The commonest disappointment in a first chestnut harvest. Float-test, refrigerate the same day, and clear the orchard floor in fall - do those three and the problem stays small.

A water-mold root and collar rot (Phytophthora cinnamomi and relatives) and the second great killer of chestnuts after blight - historically it destroyed chestnut orchards across the American South and southern Europe before blight ever arrived. It attacks the roots and root collar in wet, heavy or poorly drained soil, rotting the tissue and cutting off water to the crown, so the tree yellows, thins and dies from the top down over one or more seasons. The name comes from the blue-black staining and bleeding that appears at the base of an infected trunk. Chinese chestnut carries more resistance than American or European chestnut, but no chestnut survives waterlogged ground.

Watch for: Overall yellowing, undersized leaves, thin canopy and dieback starting at the top of the tree. Dark, inky, wet-looking staining or bleeding at the root collar and lower trunk. Reddish-brown discoloration under the bark at the base when cut into. Decline concentrated in low, wet or compacted parts of the site, and worsening after a wet season.

Prevent: Site selection is the whole defense, and it happens once. Plant on deep, well-drained, slightly acid sandy or loamy soil, preferably on a slope; never plant a chestnut in heavy clay, a low wet spot, or ground where water stands after rain. Do not overwater established trees or run irrigation against the trunk. Keep mulch pulled back from the root collar so it does not stay wet. Buy trees from a clean nursery, since the pathogen moves in infested soil and container media.

Treat: There is no practical cure once a tree is infected - improve drainage immediately, pull soil and mulch away from the collar, and stop supplemental water. A declining tree is usually lost, and replanting a chestnut into the same wet spot repeats the result; move to a well-drained site instead. This is a disease you prevent by where you dig the hole.

The reason this file insists on drainage and pH before anything else. Wet clay kills chestnuts as reliably as blight does, and far less dramatically.

Squirrels are the single biggest obstacle between a home chestnut tree and a harvest. They start on the burrs while the nuts are still green, cut whole burrs off the tree, and clear the ground drop within a day - caching far more than they eat. Chipmunks and blue jays work the same crop. Because a mature chestnut is a 40-60 foot tree, none of the usual fruit defenses apply: there is nothing to net and nothing to cage. Voles are the other half of the problem and the more serious one for a young tree: they chew bark off the trunk at ground level under mulch and winter snow, and a stem girdled right around is dead in spring.

Watch for: Cut green burrs and shredded husks scattered under the tree well before the crop is ripe, and a canopy visibly thinning of burrs. A day's nut drop simply gone when you come out the next morning. Squirrels working the branches at dawn and dusk in September and October, and caching activity in nearby beds and lawn. On young trees, gnawed bark at the base, especially where mulch or long grass sits against the trunk, and vole runways showing when the snow melts.

Prevent: Gather every single day through the drop - promptness is the entire defense, and a drop left for two days is usually a drop lost. Some growers pick nearly-ripe burrs by hand and open them under cover to beat the wildlife outright. Keep the orchard floor short and clear so caching is less attractive and so you can see what has fallen. For voles, pull mulch and grass back from the trunk, fit a wire mesh guard around the base of every young tree, and keep the guard in place through winter. A metal trunk baffle can slow squirrels on a young tree, though it stops mattering once branches from anything else reach the canopy.

Treat: There is no way to exclude squirrels from an open, mature nut tree, so the realistic answer is speed and volume: gather daily, plant more than one tree, and accept a share going to wildlife. Trapping is largely futile, since new squirrels move into cleared territory within weeks. Vole damage is the one you can act on - clear cover, fit guards, and check young trunks each winter; a tree girdled all the way round rarely recovers, so this is prevention rather than treatment.

Namespaced deliberately: the generic squirrels-and-rodents record in this catalog is authored around bulbs and shrubs and reads wrongly on a 50-foot tree, where netting is not an option and daily gathering is the whole strategy.

Deer are the largest garden problem across much of the country, and where pressure is high they set the limit on what you can grow at all. They browse at night and around dawn and dusk, taking tender shoots, leaves, buds, flowers, and fruit within about five feet of the ground, and they come back night after night to anything they have found and liked. Because they have no upper incisors they tear rather than cut, leaving ragged stem ends - that is how you tell deer damage from a rabbit's clean angled cut. In fall, bucks rub their antlers on young trunks and can strip the bark right around a stem, which kills a young tree outright. Palatability varies enormously between plants and between seasons: a herd short of food in late winter eats things it ignores in June, and no plant is truly deer-proof.

Watch for: Growth cleanly missing overnight, with the plant browsed back to a level line about as high as a deer can comfortably reach. Ragged, torn stem ends rather than the clean angled cut a rabbit leaves - the single most reliable identifier. Buds and flowers gone while the foliage below is untouched, since deer often take the best part first. Hoof prints and droppings in soft ground near the damage. Repeat visits, with fresh damage each morning once a planting has been found. On young trees, shredded and stripped bark and broken low branches in autumn - that is antler rubbing rather than feeding.

Prevent: Fencing is the only thing that reliably works. Eight feet is the standard for excluding deer, or two parallel four-foot fences a few feet apart, which they will not jump because they cannot judge the landing. Short of that, cage individual plants: a sturdy wire cage or trunk guard around every young tree, left on until the trunk is thick and the canopy is above browse height, prevents both browsing and antler rubbing and is the single highest-value thing you can do for a young tree. Repellent sprays do help at moderate pressure, but they wash off and deer habituate, so reapply after rain and rotate between different types through the season. Motion-activated sprinklers, scent deterrents, and noise devices work for a while and then stop. Siting matters too: plants close to the house, in daily traffic, and screened behind other planting get browsed less than the same plant out at the boundary.

Treat: There is no chemical fix, only exclusion and recovery. Get physical protection up immediately after the first damage, because deer return to a known meal, and reinforce or rotate whatever you were relying on before. Most plants regrow from browsing if the crown and roots are intact - feed and water a grazed plant and protect the regrowth while it comes back. What does not recover in the same season is anything whose buds or flowers have been taken, and a young tree whose bark has been rubbed right around the trunk is usually lost. Where deer pressure is genuinely heavy, the honest answer is to fence properly or to grow the plants deer leave alone, rather than to keep replacing losses.

Young chestnuts are at real risk for their first several years: browsing checks growth, and autumn antler rubbing on a sapling trunk kills it outright. Cage every young trunk from planting day and leave the cage on until the bark is thick and the canopy is above reach. Deer also clean up fallen nuts, which matters less.

A tiny introduced wasp (Dryocosmus kuriphilus) whose larvae cause swollen green-to-reddish galls on developing buds, shoots and leaf stalks. Galled shoots never extend properly, so a heavily infested tree loses much of its new growth, sets few nuts, and declines over several seasons. It spread through the southeastern US after arriving in Georgia in the 1970s and is the reason several states regulate the movement of chestnut nursery stock - the wasp travels inside dormant buds on nursery trees.

Watch for: Round or irregular green, pink or reddish swellings at bud, shoot and leaf-stalk positions in late spring and early summer, later drying to hard brown woody galls that persist on the twigs. Shoots that fail to elongate, with tufted, distorted leaves. A noticeable drop in nut set on an otherwise healthy tree. Old dry galls still on the twigs in winter.

Prevent: Buy nursery stock from a reputable source and check your state's rules on moving chestnut planting material, since the wasp is carried in dormant buds. Prune out and destroy galled shoots in late winter before the adults emerge in early summer. Keep trees vigorous - a strong tree tolerates a moderate infestation. Some Chinese cultivars are notably more tolerant than others; ask the nursery.

Treat: There is no effective home spray, because the larvae are protected inside the gall for most of their life. Pruning out galls before emergence is the practical measure. In much of the infested range the parasitic wasp Torymus sinensis, introduced for biological control, has substantially reduced gall wasp populations over time, so an outbreak that looks alarming often subsides across several seasons.

Rarely kills a tree but can suppress growth and nut set for a few years. Winter is the easy time to spot and prune out old galls.