Combating Japanese Beetles

Japanese Beetle (Popillia japonica)

Japanese Beetle (Popillia japonica)

Japanese Beetles (Popillia japonica) are especially prolific this summer, voraciously consuming the leaves, flowers and buds of herbaceous (non-woody) plants, shrubs and trees. They were first discovered at a nursery in New Jersey in 1916, probably introduced here with imported nursery stock. Now widespread east of the Mississippi River in the United States and southern Canada, these insects are destructive pests in North America because the natural predators with which they evolved are not present here to keep them in check.

Red Chokeberry (Photinia Pyrifolia) leaves skeletonized by Japanese Beetles

Red Chokeberry (Photinia Pyrifolia) leaves skeletonized by Japanese Beetles

What can you do to combat these critters? Enlist the help of some predatory insects that are native to North America.

Scolia dubia on Boneset (Eupatorium species). Scolia dubia is known to prey on the larvae of Japanese Beetles.

Scolia dubia on Boneset (Eupatorium species). Scolia dubia is known to prey on the larvae of Japanese Beetles.

Scoliid wasps prey on the larvae of scarab beetles to feed their own larvae. Japanese Beetles are a species of scarab beetle. Female Japanese Beetles burrow a few inches into the ground to lay their eggs. Their larvae, often called grubs, develop underground and feed on the roots of plants. Female scoliid wasps find and enter the underground burrows of Japanese and other scarab beetles, and lay an egg on each grub. The wasp larva hatches and consumes the grub.  Two species of scoliid wasps are shown in this post, Scolia dubia and Scolia bicincta.

Scolia dubia on Grass-leaved Goldenrod (Euthamia graminifolia)

Scolia dubia on Grass-leaved Goldenrod (Euthamia graminifolia)

How can you entice these beneficial wasps to patrol your property? They can be bought with food. The adult wasps drink nectar from flowers, usually flowers that have short tubes, arranged in dense clusters that provide a landing platform for the wasp. Mountain mints and many aster family members fit this description. They seem especially partial to goldenrods and bonesets, in addition to the mountain mints.

Scolia bicincta on Hoary Mountain Mint (Pycnanthemum incanum). Scolia bicincta may also be a Japanese Beetle predator.

Scolia bicincta on Hoary Mountain Mint (Pycnanthemum incanum). Scolia bicincta may also be a Japanese Beetle predator.

These beneficial wasps are hairy, helping to make them to be effective pollinators of the plants they visit for nectar. The pollen is likely to adhere to their hairy bodies and be carried to another plant for deposit.

Scolia bicincta on Hoary Mountain Mint (Pycnanthemum incanum).

Scolia bicincta on Hoary Mountain Mint (Pycnanthemum incanum).

You may be worried about having wasps around, because of their reputation for stinging. While that reputation may be deserved for some social wasp species, like the Yellowjackets, it’s more a case of guilt by hasty generalization for solitary wasps like the scoliids. Social wasps live in colonies, which they aggressively defend from intruders. But scoliids, like many wasp species, are solitary. So there is no colony to defend. Stingers are really ovipositors (egg laying structures) that can be used for two purposes. Females may use the ovipositor to sting and subdue their prey, and also to lay their eggs. Male wasps and bees don’t lay eggs, so the don’t have ovipositors, and can’t sting. Solitary wasps like the scoliids are quite gentle, and would generally have no reason to sting a person.

Eastern Yellowjacket (Vespula maculifrons) on Goldenrod (Solidago species)

Eastern Yellowjacket (Vespula maculifrons) on Goldenrod (Solidago species)

The Wheel Bug (Arilus cristatus) is a type of assassin bug that is happy to devour adult Japanese Beetles. Wheel Bugs hunt their prey by blending in with a plant. They wait for a hapless victim to come close enough to grab it with their somewhat hairy and sticky front legs, then stab it with their beak, injecting enzymes that paralyze and then liquefy their victim’s innards. The Wheel Bug then slurps up the resulting insect smoothie, with the victim’s exoskeleton acting as a to-go cup.

Wheel Bug (Arilus cristatus) preying on Japanese Beetle; more Japanese Beetles continue to eat in upper left.

Wheel Bug (Arilus cristatus) preying on Japanese Beetle; more Japanese Beetles continue to eat in upper left.

Japanese Beetle grubs (larvae) are especially fond of eating the roots of lawn grasses. As a result, lawns are the favored location for Japanese Beetles to excavate a burrow for their eggs. Replacing as much lawn as possible with a mix of herbaceous plants, shrubs and trees will minimize the habitat available to Japanese Beetles for reproduction. Reduced habitat means fewer Japanese Beetles.

Japanese Beetles (Popillia japonica)

Japanese Beetles (Popillia japonica)

What can you do to combat Japanese Beetles?  In order to attract beneficial insects like those shown here, be sure you have a variety of plants native to your area. Take away the Japanese Beetle’s preferred habitat by minimizing the size of your lawn. There will be a corresponding reduction in the number of Japanese Beetles you see.

Spicebush (Lindera benzoin) leaf skeletonized by Japanese Beetles

Spicebush (Lindera benzoin) leaf skeletonized by Japanese Beetles

 

Related posts

Mountain Mints are Pollinator Magnets!

Asters Yield a Treasure Trove

Fall Allergies? Don’t Blame Goldenrod!

 

Resources

Eaton, Eric R.; Kauffman, Ken. Kaufman Field Guide to Insects of North America. 2007.

USDA Japanese Beetles

Beneficial Insects in the Garden

 

 

American Beech

American Beech (Fagus grandifolia)

American Beech (Fagus grandifolia)

It can be surprising  to see leaves clinging to deciduous trees in mid-winter.  In eastern North America, some oak species and American Hophornbeam (Ostrya virginiana) may retain their leaves but American Beech (Fagus grandifolia) trees are among the most conspicuous to do so.  By January its leaves are bleached to a papery pale tan, catching the bright winter light while fluttering in the winter wind.  The leaves look delicate, but give one a tug and you’ll see how tenaciously they adhere to their branches.  American Beech leaves typically stay on the trees until early spring, withstanding the effects of even ice and snow.

American Beech (Fagus grandifolia), in March

American Beech (Fagus grandifolia), in March

Why do American Beech and other trees keep some of their leaves in winter?  There are many theories:  the dry leaves may be a deterrent to winter browsing by deer, moose and other mammals;  holding some of the leaves until spring may be the trees’ way of time-releasing some nutrients for recycling into the soil;  the leaves may funnel more snow melt to the tree’s root system.  But no one knows for certain what caused this trait.

The smooth, pale gray bark is an unmistakable characteristic of American Beech, often tempting passers-by to carve their initials.  A more interesting possibility is a sighting of animal ‘tracks’ – claw marks from animals that may have climbed the tree at some point.

Animal 'tracks' on American Beech (Fagus grandifolia)

Animal ‘tracks’ on American Beech (Fagus grandifolia)

Trees are susceptible to frost cracks in winter, caused by warming from the low-angled rays of the winter sun, followed by rapid cooling when the sun sets or disappears behind a cloud.  Both the bark and the wood it encompasses expand in the warm sun, but the bark may cool more quickly than the wood when the sun disappears, causing lengthwise cracks to occur in the bark.  If temperatures are warm enough, portions of the inner bark may become active, only to be killed if a rapid refreeze occurs.  American Beech evolved to minimize the harsh effects of the sun by having light-colored bark that reflects the sun’s rays.  The winter leaves may provide an additional layer of protection from the warm sunlight.

American Beech’s long, sharply pointed copper-colored buds are another distinctive winter identification feature.

American Beech (Fagus grandifolia) buds

American Beech (Fagus grandifolia) buds

As spring approaches, American Beech buds grow longer and plump, eventually opening to reveal newly unfurling leaves, accordion pleated and hairy as they first emerge.  The long silky hairs are an adaptation to make the new leaves less appealing to the many species of hungry caterpillars and other insects that may eat the leaves later as the hairiness dissipates.

Newly unfurled leaves of American Beech (Fagus grandifolia)

Newly unfurled leaves of American Beech (Fagus grandifolia)

According to Bringing Nature Home by Douglas Tallamy, American Beech provides food for the caterpillars of over 100 species of butterflies and moths.  Among them is the Early Hairstreak butterfly, a rare species found in deciduous or mixed woodlands from the maritime provinces of Canada to northern Michigan and Wisconsin through the Appalachians to Tennessee and North Carolina.  Early Hairstreak caterpillars can only eat the leaves of American Beech and Beaked Hazelnut (Corylus cornuta).  The presence of caterpillars attracts predatory insects and arachnids to feed on them, including many species of spiders, wasps, ants and flies.  These insects are beneficial to the trees, because they help keep the caterpillar population in check.

In addition to butterfly and moth caterpillars, a few of the insects that use American Beech include Leaf-footed Bugs,

Leaf-footed Bug (Acanthocephala species) on American Beech (Fagus grandifolia)

Leaf-footed Bug (Acanthocephala species) on American Beech (Fagus grandifolia)

leaf-rollers,

Insect shelter, likely leaf-rolling weevil nest

Insect shelter, likely leaf-rolling weevil nest

and Woolly Beech Aphids.

Woolly Beech Aphids (Phyllaphis fagi)

Woolly Beech Aphids (Phyllaphis fagi)

The Woolly Beech Aphids’ honeydew in turn attracts other insects who eat it, including wasps and ants.

Ants harvesting Woolly Beech Aphid Honeydew

Ants harvesting Woolly Beech Aphid Honeydew

Ants help protect the tree from the insects that feed on its leaves, by aggressively attacking them.

The Harvester butterfly also feeds on the Woolly Beech Aphid’s honeydew, although its first choice is Wooly Alder aphids.  The Harvester’s caterpillars eat the aphids themselves.

Harvester Butterfly

Harvester Butterfly

A non-native scale insect (cryptococcus fagisuga) introduced through the nursery trade on European Beech threatens the health of American Beech by providing an opening in the bark that together with a fungus enables beech bark disease.  This is a good example of the importance of using native plants in your own garden, and the danger of using introduced exotic plants.

There is a fungus species that grows exclusively on the Woolly Beech Aphid’s honeydew, a sooty mold descriptively named Beech Aphid Poop-eater (Scorias spongiosa).  Some studies have shown that leaves covered in sooty molds are more effective at removing pollution from the air than other leaves are.

Beech Aphid Poop-eater (Scorias spongiosa)

Beech Aphid Poop-eater (Scorias spongiosa)

Oyster (Pleurotus ostreatus) and Burnt-Orange Bolete (Tylopilus ballouii) mushrooms, both edible, are among the other fungi that may be found on or near American Beech.

American Beech develops natural cavities that provide nesting sites for cavity nesting birds like Titmice, Chickadees, Woodpeckers and Nuthatches, all of whom rely on insects for a large part of their diet, and will help protect the tree from insect leaf-eaters.  Chipmunks, squirrels, porcupines and other mammals also take advantage of the natural shelter American Beech offers.

Gray Squirrel in cavity of American Beech

Gray Squirrel in cavity of American Beech

Other birds, like the Wood Thrush below, may nest on the limbs of American Beech, using some of the previous year’s fallen leaves as nesting material.

Wood Thrush on her nest in an American Beech. Some old Beech leaves have been used as nest material.

Wood Thrush on her nest in an American Beech. Some old Beech leaves have been used as nest material.

American Beech’s fallen leaves may offer insect protein for ground-feeders like the Ovenbird.

Insect nest on fallen American Beech leaf

Insect nest on fallen American Beech leaf

Ovenbird in American Beech

Ovenbird in American Beech

Beechdrops (Epifagus virginiana) depends on American Beech for its survival, since it gets its food from the tree’s roots.  Look for the flowers in late summer or early fall, and the brown seed capsules throughout the winter.

Beechdrops (Epifagus virginiana) flowers

Beechdrops (Epifagus virginiana) flowers

Beechdrops (Epifagus virginiana) in winter

Beechdrops (Epifagus virginiana) in winter

American Beech flowers are wind pollinated, with separate male and female flowers both on the same plant.  They bloom as the leaves are opening.

Male flowers of American Beech (Fagus grandifolia)

Male flowers of American Beech (Fagus grandifolia)

Nuts are produced if the flowers are successfully pollinated, usually 2 or 3 three-sided nuts per husk.

American Beech (Fagus grandifolia) nuts

American Beech (Fagus grandifolia) nuts

The nuts are a source of high protein and fat for mammals and birds, including red, gray and flying squirrels, chipmunks, bears, Blue Jays, Tufted Titmice, Wild Turkey, and Ruffed and Spruce Grouse.

Tufted Titmouse eating American Beech nut

Tufted Titmouse eating American Beech nut

Nothing goes to waste in nature, so an empty beechnut husk may be reused as a shelter by an insect.

Insect nest in husk of American Beech

Insect nest in husk of American Beech

As the nights get longer and the temperatures drop in the fall, the American Beech begins to prepare for winter.  The leaves gradually stop producing chlorophyll, which reduces the green color visible in the leaves, revealing the yellows and oranges of carotenes, and the brown tannins, .

American Beech (Fagus grandifolia) leaf in fall

American Beech (Fagus grandifolia) leaf in fall

American Beech is native in moist woodlands in the eastern United States and Canada.  The bounty of insects supported along with its nutritious nuts makes it one of our most valuable tree species for wildlife.

Golden-crowned Kinglet in American Beech

Golden-crowned Kinglet in American Beech

 

Resources 

Cech, Rick; Tudor, Guy.  Butterflies of the East Coast.  2005.

Eastman, John.  The Book of Forest and Thicket.  1992.

Eaton, Eric R.; Kauffman, Ken.  Kaufman Field Guide to Insects of North America.  2007.

Lincoff, Gary H.  National Audubon Society Field Guide to North American Mushrooms. 1981

Rhoads, Ann Fowler; Block, Timothy A.  The Plants of Pennsylvania.  2007

Tallamy, Douglas W.  Bringing Nature Home, 2007,

Wojtech, Michael.  Bark A Field Guide to Trees of the Northeast.  2011.

USDA NRCS Plants Database

Tom Volk’s Fungi

iNaturalist.org
http://www.inaturalist.org/taxa/144013-Scorias-spongiosa

Butterflies and Moths of North America http://www.butterfliesandmoths.org/species/Erora-laeta

Illinois Wildflowers
http://www.illinoiswildflowers.info/trees/plants/am_beech.htm

Penn State Extension Natural Resources
http://extension.psu.edu/natural-resources/forests/news/2012/winter-leaves-that-hang-on

Northern Woodlands
http://northernwoodlands.org/articles/article/why-do-some-leaves-persist-on-beech-and-oak-trees-well-into-winter

Invasive.org
http://www.invasive.org/browse/subinfo.cfm?sub=300

 

An Orchid in Winter

On a walk in the woods the other day, I found what I was looking for: a leaf!   It may seem like it should be pretty easy to find a leaf on the forest floor, but I was looking for something very specific, not a fallen leaf, but the newly unfurled leaf of a native orchid called Puttyroot (Aplectrum hyemale).

Puttyroot (Aplectrum hyemale) leaf

Puttyroot (Aplectrum hyemale) leaf

Hyemalemeans winter, a reference to the fact that the leaves of this plant emerge in late November or December and are visible until spring.  Puttyroot is found in rich deciduous woodlands, often in the company of Sugar Maple (Acer saccharum) and American Beech (Fagus grandifolia).  It gathers its energy from the sun during the months when the forest canopy is open, while the leaves are off the trees.  Photosynthesis occurs in this plant at temperatures as low as 35ºF (2ºC).  During this time, Puttyroot also benefits from the nutrients released to the soil from the blanket of decomposing leaves from the neighboring trees.

In ideal conditions, Puttyroot sends up a single striped, accordion-pleated leaf in late fall, about 3-8 inches (.75 – 2 dm) long and 1-3 inches (.25 – .75 dm) wide. The leaf dies back by the time the single flower stalk blooms in May or early June.  The flower stalk height can vary from about 6 to 20 inches (1.5 – 5 dm).

Puttyroot (Aplectrum hyemale) flowers

Puttyroot (Aplectrum hyemale) flowers

Bees are likely the pollinators of Puttyroot, although the flowers can also self-fertilize if necessary.  Puttyroot’s many tiny seeds are dispersed by the wind.

Puttyroot (Aplectrum hyemale) flower

Puttyroot (Aplectrum hyemale) flower

There may be years when a Puttyroot plant doesn’t bloom, its presence only revealed by the winter leaf.  Some years the plant may be completely dormant, without even the leaf visible above ground.

This orchid species is native throughout the eastern half of the United States (except Florida) and in Quebec and Ontario provinces in Canada, but it is listed as rare, threatened or endangered throughout much of its range, including New York, New Jersey, Pennsylvania, Vermont and Massachusetts.

Non-native, invasive plants like Garlic Mustard (Alliaria petiolata) and Japanese Stiltgrass (Microstegium vimineum) are a serious threat to Puttyroot and its companion woodland plants. Not only do these invasive species compete for resources with native plants, they also alter the soil chemistry in a negative way, interfering with the mycorrhizal fungi that is present.  Most plants don’t get the nutrients they need directly from the soil, but rather through a partnership with mycorrhizal fungi.  Plants provide sugars to the fungi, and the fungi in turn make nutrients available to the plants. If the fungi aren’t present, the plants won’t get the nutrients necessary to continue to be viable.  The good news is that both Garlic Mustard and Japanese Stiltgrass are easy to remove by pulling.  Garlic Mustard is edible, so you can reward yourself for removing it by eating your ‘harvest’.  Garlic Mustard pesto, anyone?

Early settlers used a mucilaginous substance obtained from Puttyroot’s corms (part of the underground food storage system) to repair broken pottery, a practice that resulted in the plant’s common name.  Another common name, Adam and Eve, also refers to the plant’s corms, which are usually paired.

Puttyroot (Aplectrum hyemale) leaf

Puttyroot (Aplectrum hyemale) leaf

Go for a walk in the woods and see if you can find a Puttyroot leaf.  If you’re successful, make a mental note of its location.  Then visit the spot again in May or June, to see if you can find the flower stalk in bloom.  Repeat the process until you find this buried treasure!

Resources

Capon, Brian.  Botany for Gardeners.  2005

USDA Plants Database

Go Botany

New England Plant Conservation Program Aplectrum hyemale (Muhl. ex Willd.) Nutt. Puttyroot

Illinois Wildflowers

USDA National Invasive Species Information Center:
Garlic Mustard
Japanese Stiltgrass

 

 

 

 

 

Even Bald-faced Hornets Recycle

During the winter, Bald-faced Hornet (Dolichovespula maculata) nests are more visible than they are during the growing season when the woods are dense with leaves.

Bald-faced Hornet Nest in winter

Bald-faced Hornet Nest in winter

This large nest looks like it is made of paper, and in fact it is. Initially the queen, and later the workers in the colony use their mandibles to scrape up and recycle bits of dead wood, then they mix the wood with their saliva to create the paper mache like substance from which they gradually construct their nest, adding new cells as the colony grows.

Bald-faced Hornet Nest in winter.  The bottom has been removed, revealing the cells where larvae develop

Bald-faced Hornet Nest in winter. The bottom has been removed, revealing the cells where larvae develop

These nests are generally not active in winter, except occasionally in the southernmost part of the Bald-faced Hornet’s range. All the colony members die as winter sets in, with the exception of the fertilized queen. She finds a safe, warm place to spend the winter, usually in or under a fallen log, in a hollow tree, or sometimes underground.

In spring, birds take advantage of these abandoned structures and rip away bits of the paper to use as building material in their own nests. If you look at the lower right section of the nest below, it looks like there is some recycled ‘paper’ along with the plant materials that were used in this construction.

Bird's nest made from plant materials and wasp nest paper

Bird’s nest made from plant materials and wasp nest paper

Because paper is used in the construction of the nest, people often think this large football shaped shelter belongs to Paper Wasps. While Paper Wasps use the same materials for constructing their nests, the homes they build for their larvae are much smaller, and somewhat umbrella-shaped, like the one below.

Paper Wasp Nest

Paper Wasp Nest

Paper Wasp (Polistes carolinus)

Paper Wasp (Polistes carolinus)

Bald-faced Hornets are named for the white markings on their face, and are sometimes called White faced Hornets. They also have white markings on the lower part of their abdomens.

Bald-faced Hornet feeding on nectar.  Note the white facial markings that give this species its name, and the pollen on its head.

Bald-faced Hornet feeding on nectar. Note the white facial markings that give this species its name, and the pollen on its head.

Does the word ‘hornet’ make you want to reach for a can of insecticide spray? Well, don’t!  That’s almost never a good idea.

It may help to know that Bald-faced Hornets are not really hornets! They are wasps, one of the wasp species known as Yellowjackets. Ok, I get that this might not make you feel any more comfortable with them. We’re used to Eastern Yellowjackets relentlessly competing for picnic food, and they can be quite aggressive.

Eastern Yellowjacket (Vespula maculifrons) on Goldenrod

Eastern Yellowjacket (Vespula maculifrons) on Goldenrod

It’s true that if Bald-faced Hornets think you are a threat to their nest, they may sting you, so it’s best to give an active nest a wide berth. As long as you do that, you are unlikely to have an unpleasant encounter with them.

Bald-faced Hornets are actually beneficial in several ways. Like many wasp species, they help to keep the insect population in balance. Bald-faced Hornets feed many types of insects to their developing offspring, and are especially fond of flies and even other Yellowjackets. They can be helpful by harvesting caterpillars for their offspring on a farm or near a vegetable garden – think unwanted Tomato Hornworns.

Bald-faced Hornet nectaring on asters

Bald-faced Hornet nectaring on asters

Adult Bald-faced Hornets feed primarily on nectar or other sweet treats like aphid honeydew. In the process, they provide pollination services to the flowers where they are drinking. And in spite of their size and stingers (in the case of females), Bald-faced Hornets may become a meal for a larger predator.

Bald-faced Hornets can make good neighbors, as long as you give them their space.

References:

Eaton, Eric R.; Kauffman, Ken.  Kaufman Field Guide to Insects of North America.  2007.

http://ento.psu.edu/extension/factsheets/baldfaced-hornet

http://mdc.mo.gov/discover-nature/field-guide/bald-faced-hornet

http://naturemappingfoundation.org/natmap/facts/bald-faced_hornet_712.html

http://www.inaturalist.org/taxa/baldfaced_hornet

http://eol.org/pages/239818/overview

http://www.biology.ualberta.ca/bsc/ejournal/bmc_05/84d_maculata.html

http://www.clemson.edu/cafls/departments/esps/factsheets/medvet/baldfaced_hornets_mv15.html

In Praise of Black Walnut Trees

If you go for a walk in the woods any time soon, you may still encounter black walnuts or the remains of their hulls on the ground.

Fallen Black Walnuts

Fallen Black Walnuts

The nuts usually remain on the tree until after the leaves fall, reminding me of a Charlie Brown Christmas tree.  Then all the nuts fall within a short time of each other.  These nuts are sweet tasting and highly nutritious.  Studies show that eating them helps prevent cardiovascular disease, diabetes and cancer.  Walnuts have as much protein as an equal weight of beef, but they also contain essential fatty acids that are necessary for healthy brain development and function.  Any aging brains out there?  Eat walnuts!

Black Walnut (Junglans nigra)

Black Walnut (Junglans nigra)

Mammals other than humans like them, too: squirrels, mice and voles, for example.

Eastern Gray Squirrels eat and help disperse Walnuts

Eastern Gray Squirrels eat and help disperse Walnuts

Red Squirrels also enjoy many tree nuts, including Walnuts

Red Squirrels also enjoy many tree nuts, including Walnuts

These animals aid in the spread of Walnut trees when they overlook some of the nuts they have hidden away for later use, effectively planting them.

In turn, these animals are food for larger animals, like fox

Red Fox

Red Fox

and raptors.

Red-shouldered Hawks, as well as most other raptors, hunt and eat small mammals

Red-shouldered Hawks, as well as most other raptors, hunt and eat small mammals

According to Douglas Tallamy in Bringing Nature Home, the leaves of Black Walnut (Juglans nigra) trees and the closely related Butternut (Juglans cinerea) provide food for the caterpillars of over 100 species of moths and butterflies, including Luna Moths and Banded Hairstreaks.

Banded Hairstreak on Butterflyweed. Their caterpillars feed on the leaves of Black Walnut and other woody species

Banded Hairstreak on Butterflyweed. Their caterpillars feed on the leaves of Black Walnut and other woody species

The Walnut Caterpillar specializes on Black Walnut and relatives such as Butternut.  This means the leaves of these trees are the only food these caterpillars can eat.

Walnut Caterpillar (Datana integerrima)

Walnut Caterpillar (Datana integerrima)

Since they are an important source of food for birds, not all caterpillars will see life as an adult butterfly or moth.

Tufted Titmouse

Tufted Titmouse

Black Walnut trees have a reputation for not playing well with other plants. That is, many plants won’t grow successfully in close proximity (within the drip-line or reach of the roots) of a Black Walnut. The reason is more complex than shade and competition for water.  Black Walnuts contain juglone, which is an anti-fungal chemical.  In order to derive nutrients from the soil, the vast majority of plants partner with underground mycorrhizal fungi (think mushroom, not the mold in your shower).  Unless the fungi on which the plant depends is resistant to juglone, or the plant doesn’t require this partnership to obtain its nutrition, that plant won’t do well.  Of course, some plants and their fungi partners have evolved in exactly this way.  Click here for some suggestions from The Mortem Arboretum for plants that can co-habit successfully with Black Walnut trees.

It’s of benefit to Black Walnut trees to produce juglone, since it does reduce competition for resources, and protects the trees from fungal invaders that might do them harm. Juglone also has sedative properties that may aid animals in dormancy. It can even have a calming effect on people.

Black walnut trees contain another compound called ellagic acid in both their nuts and leaves. This compound is thought to help prevent cancer in people who consume the nuts. The ellagic acid in the leaves is effective in removing carcinogenic hydrocarbons from the air, helping to reduce the effects of air pollution.

As if that weren’t enough, Black Walnut’s wood is valuable for furniture and cabinet making, and the nut hulls can be used to make a dye.

Black Walnut with hull partially removed

Black Walnut with hull partially removed

These are just some of the known benefits of Black Walnut trees.  Just imagine what we don’t know yet!  No wonder ‘juglans’ is sometimes translated as ‘nut of Jupiter’, or ‘nut of the gods’.

Black Walnut Tree (Juglans nigra)

Black Walnut Tree (Juglans nigra)

Resources

Beresford-Kroeger, Diana.  Arboretum America: A Philosophy of the Forest.  2003

Eastman, John. The Book of Forest and Thicket. 1992.

Tallamy, Douglas W.  Bringing Nature Home.  2007

Wagner, David L.  Caterpillars of Eastern North America.  2005.

Butterflies and Moths of North America

Natural History Museum Database of Leipidoptera Hostplants