Beech Leaf Disease Mystery: A Nematode is the Main Suspect

By Wendy Diaz EMGV

One of the trees in the north corner of my triangle-shaped yard that has a very large presence and provides beneficial shade is a native American beech tree (Fagus grandiflora)1. I love my beech tree and it came with the house as the developer left a forested buffer along the back property boundary. Its low branches of bright green leaves and its smooth grey bark on its wide trunk contrast nicely with the rough-textured bark of the mainly tall bare narrow trunks of the pine, white oak and sweet gum trees that dominate our backyard. So, when I heard2 about a new disease called Beech Leaf Disease (BLD) affecting these beautiful trees in Northeastern Ohio, I became concerned and wanted to learn more. 

American Beech in my backyard. Photo by Wendy Diaz May 28, 2020

American Beech Primer

The American beech is an important anchor species or ‘foundational species’ which means other living organisms and the functioning of the forest ecosystem depend on these beech trees3. This important deciduous tree of our Eastern forest is slow growing and can reach about 80 feet in height and a lifespan of between 300 and 400 years1. The American beech is a common shade tree and is most recognizable by its distinctive smooth gray bark which it maintains throughout its lifespan unlike other hardwood species. The smooth light bark tempts many a knife carver and it often has letters carved in its bark along trails in the state. Its nuts are an important food source for wildlife and a favorite of blue jays. Beech trees have shallow root systems and prefer well-drained acidic soil4. The serrated oblong leaves turn golden yellow in the fall.

BLD Discovery and Spread

In 2012, Beech Leaf Disease was first discovered by John Pogacnik, a biologist, in a beech tree grove atop a ravine in Concord Township north of Columbus in central Ohio5. As of January 2019, the disease had spread as far north as southern Ontario in Canada and decimated large tracts of beech trees in many counties in Northeast Ohio, Western Pennsylvania and New York. In October 2019, the disease was confirmed in Connecticut and Long Island. It spreads about 150 miles eastward each year and movement towards the east has been rapid but movement to the west has been much slower. The map below illustrates the distribution of the BLD disease.

Image courtesy of Ohio Department of Natural Resources website

Suspected Source

To date the cause of the disease is unknown. Suspects include a new species of nematode discovered in 2017 by Dave McCann, a plant pathologist of Ohio Department of Agriculture. He observed 2mm long nematodes when he examined diseased leaves under the microscope5.  Lynn Carta, a plant disease specialist with the U.S. Department of Agriculture (USDA) in Beltsville, Maryland first described the new nematode as a subspecies of nematode described by Japanese scientists and named it Litylenchus crenatae ssb mccannii (Anguinata) 6. This is the first example of a leaf-eating nematode infecting and potentially killing a large live forest tree in North America according to L. Carta and it may have originated in a Pacific Rim country. Nevertheless, Enrico Bonello, a plant pathologist at Ohio State University, found nematodes in both healthy and diseased leaves so he attributes the true cause of the disease to a microbial pathogen and postulated that the microscopic worms may be simply transmitting the pathogen.7


BLD Symptoms

Diseased beech leaves exhibit interveinal greening or dark green bands between veins of the leaf, thickening and often chlorosis in leaves6 and sometimes leaves blister, thicken and become shriveled. Later, the diseased leaves become uniformly darker, shrink and get crinkly8,9. Eventually the canopy starts thinningand limbs stop forming new buds and eventually the tree dies. The disease has been found in European and Asian beech tree species in nurseries and at the Holden Arboretum in northeastern Ohio.

Classic dark green banding between veins of beech leaves and symptom of Beech Leaf Disease (BLD). Photo courtesy of Ohio State University Buckeye Yard & Garden online article entitled More Beech Diagnostics, author Jim Chatfield. Published on August 28, 2017
No dark banding between leaf veins in healthy Beech leaves. Photo taken by Wendy Diaz May 28, 2020

What can we do now? Not much because they don’t know how it spreads as yet10. We have to try and prevent the introduction of BLD to our southeast forests and monitor them for signs and symptoms of the disease11. USDA’s Animal and Plant Health Inspection Service, the agency responsible for dealing with invasive tree killers, is also studying the disease but is not taking action to limit the disease until more is known about how the disease spreads and its cause.7 In the meantime people can help with BLD surveys by downloading the Tree Health App3 and it is always a good practice not to move firewood between locations. If you purchase European and Asian varieties of beech trees be careful because long-range spread is probably assisted by anthropogenic transport, especially of nursery stock8. Let us hope they determine the cause and discover a remedy soon before this disease spreads south to our beech forests here in North Carolina. For now, I will pay more attention to my beech tree and spread more leaf litter over its shallow roots to prevent stress during our summer dry spells and I definitely won’t be carving my initials its smooth bark.

Closeup of smooth gray bark of the American Beech. Photo taken by Wendy Diaz May 28, 2020


  4. NCSU Plant Toolbox:
  6. Carta LK, Handoo ZA, Li S, et al. Beech leaf disease symptoms caused by newly recognized nematode subspecies Litylenchus crenatae mccannii (Anguinata) described from Fagus grandifolia in North America. For Path. 2020;00:e12580. Link (
  9. Ohio State University More beech diagnostics Jim Chatfield August 28 2017
  10. on May 17, 2020

Note: At the time of this post not all resources were accessible as the Ohio Department of Natural Resources and Division of Forestry website was under redevelopment.

June: To Do in the Garden

by Gary Crispell EMGV

The calendar claims it is June. The weather, well, the weather is about as seasonally correct as the stock market is an accurate indicator of the economy—worthless mostly. Presumably we are through covering tender vegetation until October—presumably.

The “Accidental Cottage Garden” in my front yard is still delighting and surprising every day. Now that the red clover (Trifolium praetense) has finished, the poppies (Papaver orientale) are front and center in an amazing variety of colors. The cornflowers (Centaurea montana) are fantastic. I had no idea they came in so many colors, deep red, purple, magenta, hot pink and, of course, cornflower blue. There are still several plants I have not identified. Can’t get out there with the book between rain showers. Cosmos (Cosmos bipinnatus) will be the next major player.  What’s exciting in your garden?

Cornflowers (Centaurea montana) come in many colors! Photo by G. Crispell.

Lawn Care

If you have heretofore procrastinated on this item it is TIME to fertilize warm season grasses (i.e. Bermuda, Zoysia, St. Augustine). It is also the best (and really only) time to fertilize Centipede. The general recommendation is for one-half pound 15-0-14 or equivalent per 1000 square feet. Should you desire to be truly accurate-GET a FREE SOIL TEST. Kits are available for contact-free pickup at the Cooperative Extension office, 721 Foster Street, Durham.

It would be difficult to core aerate our clayey soils too much, so a day or two after a rain (like any day this spring) or a good irrigation would be an ideal time do just that.

When mowing warm season grasses a good rule-of-thumb is to remove one-third of the new growth per mowing.

If you have been drooling over your neighbor’s Zoysia lawn, June is a good time to start your own with sod or plugs.


After getting your FREE SOIL TEST in order to avoid overfertilizing, now is the time to feed your dogwoods following the recommendations.

Vegetable gardens would like a side dressing of fertilizer about now to maximize production.


Again, for the procrastinators out there, if you want a crop this year better get these plants (too late for seeds) in the ground ASAP: tomatoes*, peppers, black-eyed peas, lima beans, green and wax beans, pumpkins, sweet potatoes.

Start (from seed) Brussel sprouts & collards to set out in mid-July.


Coniferous evergreens like pines, cedars, junipers, arborvitaes, etc. may be pruned now. (Coniferous evergreens produce seeds in cones.)

Hedges can be pruned now but be advised do not remove more than a third of the total plant top. (The green part.)

Keep pinching your garden mums until mid-July.

Hydrangea macrophylla (the ones with the BIG leaves) can be pruned when the flowers fade.

Azaleas may be pruned until July 4. (An “old wives tale” that works.)

Dieback in ericaceous plants (acid-loving) such as azalea, rhododendron, Pieris, etc. can be pruned out now.  Remember to cut below the damage and to sterilize the pruner with 10% bleach between cuts.

Pest Control & Herbicides

Patrol your shrubs for the following likely suspects: lace bugs, leaf miners, spider mites, aphids and bag worms. Use appropriate measures to curtail their destructive tendencies. If the bag worms have already bagged themselves you will have to hand pick them and destroy them in any manner you see fittin’.

June is also the beginning of the Asian invasion better known as Japanese beetles.  There is a myriad of treatment options out there.

Tomato* early blight could be rampant this year what with all the warm dampness. Watch for dark spots on the leaves and treat with an appropriate fungicide. There are some good organics out there.

June is a good month to eradicate poison ivy, kudzu and honeysuckle. Get ‘em with an appropriate herbicide while they are rapidly growing.

As with shrubs it is time to be on guard in the garden. Several (many?) insects are looking for gourmet gardens to satisfy their gastronomic inclinations. Look for a variety of worms on cruciferous veggies (cabbage, broccoli, cauliflower), cucumber beetles on cucumbers (ironically), squash borers on other cucurbits–squash and melons, flea beetles on green beans, tomatoes and eggplant, and aphids on anything green.

Continue with regular pest management programs on bunch grapes, fruit trees and roses.

Use pesticides wisely, sparingly and only when necessary. Always read the label and follow directions.

Other Fun Garden Stuff to Keep You Outside

Water lawns as necessary but try to do it early in the day to avoid evaporative loss.  Watering lawns in the evening promotes disease. Lawns and gardens need about one inch of water per week either from natural sources or irrigation. 

Strawberry beds can be renovated now.

It is also a marvelous time to sit on the deck or patio with a glass of your favorite cold beverage and enjoy your garden. And if your deck is spacious enough for six-foot distancing you can invite friends, but no more than 25. Use triangular spacing.  It’s more efficient. Wear your masks and wash your hands, again.  Stay safe, y’all.

*Speaking of tomatoes, visit our Tomato Grafting Project page for an update about this special project! Learn more

Asian Giant Hornet Not Detected Yet in NC

With the emergence of the Asian Giant Hornet in Washington State, the NC Department of Agriculture and Consumer Services is urging North Carolina residents to be vigilant and report potential sightings of the pest.

Asian Giant Hornets are the world’s largest species of hornet, measuring about an inch-and-a-half to two inches long. They have an orange-yellow head and prominent eyes, with black and yellow stripes on their abdomens. The hornet is not known to occur in North Carolina, and our state’s apiary staff have been actively monitoring for the pest with no detections to date.

“The Asian Giant Hornet is a threat to honeybees and can rapidly destroy beehives, but it generally does not attack people or pets,” said Agriculture Commissioner Steve Troxler. “There are many wasp and hornet look-alikes that are beneficial insects, so residents are asked to exercise caution before deciding to kill any large hornets.”

Cicada killers and European hornets do occur in North Carolina and can be confused with the Asian Giant Hornet. Residents can visit to see a photo of the Asian Giant Hornet along with common look-alikes.

If you think you have seen an Asian Giant Hornet, take a photo and submit it to the North Carolina State University’s Plant Disease and Insect Clinic. Instructions on digital submission can be found at  under Option 3.

For more information about the Asian Giant Hornet, visit the NCSU Cooperative Extension or read our pest alert at https:///