Extension Master GardenerSM Volunteers of Buncombe County

Trees

Pest Facts: Hemlock Woolly Adelgid (HWA)

Just visit a Western North Carolina forest to see how much destruction this non-native invasive insect pest has caused—and is still causing—on the native Carolina hemlocks (Tsuga caroliniana) and Eastern hemlocks (Tsuga canadensis)! After our recent rains, this is a good time to treat your hemlocks if you see a white cottony substance on your hemlocks.

Hemlock Woolly Adelgid

History

  • HWAs were discovered in Shenandoah National Park in northern Virginia in 1988, likely when crawlers clung to the legs and feathers of migrating birds, such as the black-throated green warbler and solitary vireo that visit or nest in hemlock trees.
  • HWAs were discovered on hemlocks in North and South Carolina in late 2001 and early 2002.

HWA (Adelges tsugae) Life Cycle:

  • HWAs hatch from eggs and then go through a crawler stage—almost invisible to the naked eye. These crawlers cannot fly on their own but can drift in the air from tree to tree, and cling to the legs and feathers of migrating birds.
  • After settling on host trees, the HWAs insert a bundle of mouthparts at the base of a needle and spend the rest of their lives—a few months—sucking nutrients out of the tree.
  • The name “woolly” comes from the fact that adult HWAs are covered with a protective white fluff once they settle.
  • The HWA goes through two generations a year (one in March and one in October in Western North Carolina) and each female—even without being fertilized by a male—can lay between 100 to 300 eggs.
  • This reproductive process is called “parthenogenesis”—the offspring are genetically identical clones of their mother.

Controls

Chemical: Registered pesticides containing imidacloprid or dinotefuran are the most effective chemical treatments for control of HWAs. These are applied as a soil injection or trunk spray. These insecticides are water soluble and move into the tree’s vascular system along with water. Dinotefuran has a faster uptake, but imidacloprid has a longer residual protection. Control of HWAs using imidacloprid can last for 4-5 years. Dinotefuran may require retreatment within 2 years.

Biological:

The species that has so far shown the most promise as a biological control agent is Laricobius nigrinus, a predator beetle native to the Pacific Northwest. L. nigrinus is active from October to March; both adults and larvae will consume all stages of HWAs: eggs, nymphs and adults.

After exhaustive evaluation in quarantine labs, it was cleared by the USDA for use as an HWA biocontrol in the eastern United States in 2000 and has been released in NC since 2003.

Original Article by Glenn Palmer, Extension Master GardenerSM Volunteer, Revised by Bob Wardwell, Extension Master GardenerSM Volunteer

Hemlock Restoration Initiative https://savehemlocksnc.org/

National Park Service Great Smoky Mountains Hemlock Woolly Adelgid

https://www.nps.gov/grsm/learn/nature/hemlock-woolly-adelgid.htm

University of Massachusetts HWA Fact Sheet https://ag.umass.edu/landscape/fact-sheets/hemlock-woolly-adelgid

What Are Those Purple Flowering Trees—Native Redbud or Invasive Paulownia?

Are you seeing signs of spring? After the bold yellow forsythia blooms, purple-flowering trees will soon brighten our yards and hillsides. What are those lovely trees? In March and April in Western North Carolina, these are most likely the native eastern redbud (Cercis canadensis). By late April or May, you’ll see larger purple flowers on the invasive Princess tree (Paulownia tomentosa). 

Eastern redbud_Cercis canadensis 'Silver Cloud'_UGA College of Ag_CC BY-NC 2.0_Flickr
Eastern redbud tree (Cercis canadensis)

About Redbuds
The eastern redbud is a small deciduous tree—15 to 30 feet tall and 15 to 25 feet wide—native to North America, ranging as far north as Canada, south as Florida, and west to Texas.

The pink to reddish-purple flowers emerge in early spring on old branches and trunks, before the leaves. After blooming, the heart-shaped leaves emerge and mature to a dark green, turning yellow to yellowish orange by fall. The trees produce clusters of green seed pods that look similar to snow peas, but brown when mature.

In the wild, eastern redbud occurs as an understory tree, preferring moist, well-drained soil, but adaptable to a range of soil conditions, and hardy from USDA zones 4 to 9.  The trees will tolerate full sun and both alkaline and acidic soils. In WNC, the trees are usually more numerous on south-facing slopes with more sunlight. They are fire-tolerant and will sprout back from the roots after a fire.

Uses
Redbud nectar attracts butterflies and hummingbirds. Pollen feeds honeybees. Birds and squirrels may feed on the seeds. Redbuds are in the pea family—their edible flowers taste like peas, making them a colorful and tasty addition to a spring salad—but only if the trees are untreated with pesticides. Some Native Americans and folk healers use the bark and roots to produce teas and tinctures to treat various ailments. 

Diseases and Pests
These beautiful trees are usually free of serious disease and pests, but are relatively short-lived, typically declining from disease after twenty years. The most common culprit is the fungal disease, Botryosphaeria canker, which can encircle the branches, effectively cutting off the water supply to the leaves, leading to branch drop. Keep plants as healthy as possible by watering regularly during dry periods and pruning out diseased branches with disinfected tools. Verticillium wilt, another serious fungal disease, blocks the tree’s vascular system from taking up water and nutrients. Leaf anthracnose and other leaf spot diseases may affect the tree’s appearance but not its overall health.

Insects that feed on redbuds include treehoppers, caterpillars, scales, and leafhoppers. For serious infestations, contact your local Extension office for treatment options.

Cultivars
Eastern redbuds are lovely native trees that are valued in our landscapes. Several redbud varieties are available. Check out some of these selections to see what strikes your fancy.

‘Alba’ (white flowers)
‘Appalachian Red’ (hot pink flowers)
‘Covey’ (dwarf weeping habit)
‘Flame’ (double flowers, seedless)
‘Forest Pansy’ (purple foliage, pink flowers)
‘Ruby Falls’ (purple foliage, weeping habit)
‘Silver Cloud’ (variegated green and white foliage)
‘Hearts of Gold’ (golden foliage)

Avoid the Paulownia!
The Paulownia or Princess tree also blooms in spring with panicles of purple flowers. Paulownia was introduced in the mid-1800s as an ornamental landscape plant. It is now considered an ecological hazard, especially to Linville Gorge and along I-40 near the Tennessee state border. Princess trees are invasive everywhere in our area and are not recommended as landscape plants. Eliminate volunteers before they establish.

Article written by Barbara Hayes, Extension Master GardenerSM Volunteer.

More information
Eastern redbud plant description
by NC State Extension

Eastern Redbud Plant Fact Sheet
by U.S. Department of Agriculture

Paulownia or Princess tree plant description
by NC State Extension

What Are the Purple-Flowered Trees? Paulownia and Oriental Wisteria
by Alison Arnold, Extension Agent, NCSU

Time to Maintain: How to Prune Deciduous Trees

Deciduous trees are ones that lose their leaves in the fall. Examples include oaks (Quercus spp.), hickories (Carya spp.), maples (Acer spp.), and sourwood (Oxydendrum arboreum) trees. Their autumn color display is long gone and the trees have entered their dormant period for the winter. Now is the time to consider pruning.

Pole Saw_99th Air Base_Lawrence Crespo_CC BY-ND 2.0_Flickr
Tree pruning with pole saw

Advantages of pruning
Proper tree pruning can add form and structure. Removing dead and damaged limbs leads to healthier trees and reduces the risk of insect attacks and infection with diseases.

What you’ll need
The first step is making sure you have the correct tools. Tree pruning typically requires:

  • Sharp hand pruners to remove smaller twigs and branches less than 1 inch in diameter.
  • Heavier pruners commonly called “loppers” for branches 1 to 3 inches in diameter.
  • Hand saw for branches and limbs 3 to 5 inches in diameter.
  • Pole saw—which will extend to about 10 feet—if you need to remove branches up to that height.

 Cautions
Using ladders when trimming requires extreme caution! Do so only when you have someone who is able to steady the ladder for you while you climb. Limbs and branches greater than 5 inches in diameter and any pruning more than 10 feet off the ground require the use of gasoline-powered chain saws and specialized climbing equipment. Unless you are trained and certified in the use of such equipment, hire a certified arborist or tree company that is fully insured!

What to prune
Once you remove a limb or branch you cannot put it back, so use caution when approaching any pruning decision! Take time to walk around the entire tree and envision what it will look like when you complete the work.

First consider removing branches growing directly toward the house or that impede your ability to walk under the tree. Once these are removed, take a step back and evaluate how to proceed. Next to go are dead branches and limbs that are rubbing against other limbs.

Pruning small branches: When pruning small branches, always cut back to a vigorously growing branch or bud that points in the direction you want the branch to grow. Cut about 1/4 inch above the branch or bud to avoid leaving a perceptible stub. This will minimize any damage to the branch collar that might occur if you cut any closer.

Limb Collar Intact_Freshly pruned silver maple_Eli Sagor_CC BY-NC 2.0_Flickr
Correctly pruned tree leaves limb collar intact.

Pruning larger limbs: Branches greater than 3 inches in diameter require three cuts:

  • Make the first cut away from the trunk to avoid “stripping” the bark. Start about 6 inches from the trunk and begin to cut up from the bottom of the branch, stopping when you’re a third of the way through the branch.
  • Make your second cut from the top of the branch, in line with the bottom cut so the limb will fall from the tree.
  • Your final cut will remove the stub that remains. This cut should be made flush with the “limb collar” at the base of the branch, not flush with the trunk.
Topping weakens a tree's structure, health, and beauty.
Tree topping – unsightly and unhealthy

Pruning practices to avoid!
Tree topping: Never “top” your trees! Although this technique is often seen in the landscape, it is the surest way to have your trees decline in vigor and health. Topped trees develop multiple secondary branches that are problematic aesthetically and weaken the trees’ structural integrity. No responsible arborist or tree company will recommend topping trees.

Wound dressings: Do NOT dress tree wounds under any circumstances! Researchers have shown that commercial products for tree wounds—paint, tar, varnish, or other such materials—trap moisture and increase disease problems. 

Learn more
Trees and Shrubs: General Pruning Techniques
https://content.ces.ncsu.edu/general-pruning-techniques

Article written by Bob Wardwell, Extension Master GardenerSM Volunteer.

Contact Us

Buncombe County Extension Office
49 Mount Carmel Road
Asheville, NC 28806
Helpline 828-255-5522

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