Extension Master GardenerSM Volunteers of Buncombe County

insects

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

Kids Post: What is chewing the trees?

In fall we watch for tree leaves to turn pretty colors—but before they turn you may see that a lot of those leaves are being chewed up! What eats tree leaves?

Leaf chewers

Although many people call leaf chewers “worms,” most aren’t worms at all! They are the early stages—called larvae—of a variety of insects.

Caterpillars are larvae that grow up to be butterflies or moths. Although many caterpillars eat plants such as milkweeds or members of the carrot family—including parsley and dill—some prefer trees!

  • Inchworms (fall cankerworms) are fun to watch because they move by inching along, but they can do lots of leaf damage to many of our most popular trees, including maples, oaks, beeches, and hickories. The adults are gray moths; the males have wings, but the females are wingless!
  • Inchworm

    Fall cankerworm wingless female moth
  • Catalpa worms can eat most all the leaves off catalpa trees during the summer—they become sphinx moths!
  • Catalpa worm

    Catalpa worm damage
  • Orangestriped oakworms strip leaves from many types of oak trees as fall approaches—they become orange moths with a white spot on each wing.

  • Orange striped oakworm
  • Fall webworms are another moth caterpillar whose larvae eat the leaves of many trees— birches, cherries, crabapples, hickories, sourwoods, and walnuts—they live inside a web until they are ready to form a cocoon to become a fluffy white moth next spring.

  • Fall Webworm (Hyphantria cunea)_James Emery_CC BY 2.0_Flickr
    Fall webworms

Sawfly larvae grow up to be sawflies—they are small flying insects that lives such short lives that you may never see the adults—or mistake them for wasps if you do! The good news is they cannot sting. Their larvae can do a lot of damage to trees and shrubs, though. Dogwood sawfly larvae may “skeletonize” the leaves of many types of dogwoods, leaving just the leaf veins!

Dogwood sawfly larvae
Dogwood sawfly larvae damage

What can you do about leaf chewers?

Birds and predatory insects feed on these critters, helping manage the damage! Also, most of these leaf chewers do their eating late enough in the year that the trees will soon drop their leaves anyway, so most don’t suffer any serious harm.

  • Catalpa worms eat a bit earlier in the summer, though, and if you love to fish, you can help save tree leaves by collecting these chewers to use as bait!
  • You can stop fall webworm damage by disturbing the web—get an adult to help you cut off any of the webbed areas, use a stick to tear up the web, or use a strong stream of water from a garden hose to bust up the web!
  • Some years fall cankerworms can eat almost all the tree leaves, producing a lot of droppings— their swinging down on spiderweb-like strands bothers some people, too! You can ask an adult to help you trap the new female moths as they crawl up the trees later this fall, once the leaves have dropped and we’ve had a freeze. The City of Charlotte has instructions for how to make sticky band traps: https://charlottenc.gov/Engineering/LandscapeManagement/Trees/Documents/CankerwormBrochure2017.pdf#search=fall%20cankerworm

Article by Debbie Green, Extension Master GardenerSM Volunteer

 For More Information:

Inchworms (fall cankerworm):

https://content.ces.ncsu.edu/fall-cankerworm

Catalpa worms:

http://capitalnaturalist.blogspot.com/2015/07/catalpa-sphinx-moth-caterpillars.html

Orangestriped oakworms:

https://content.ces.ncsu.edu/orangestriped-oakworm

Fall webworms:

https://www.buncombemastergardener.org/tag/fall-webworms/

Dogwood sawfly:

https://hortnews.extension.iastate.edu/2009/8-12/sawfly.html

 

 

Vegetable Garden Pests: Beware the Pickleworm!

Just inside from harvesting vegetables, I heard yelling from the kitchen. She was staring at a freshly washed cucumber in the sink. Sprouting from it were green projections that were alive and wriggling! This was our introduction to the insect pest with the unique name of pickleworm.

These critters are the larvae of the pickleworm moth (Diaphania nitidalis), which overwinters in Florida and becomes a late summer pest of cucurbits (not only cucumbers, but summer and winter squash, pumpkins, cantaloupe, and watermelons) in Western North Carolina.

Adult Pickleworm Moth

Life cycle

Once the moths arrive in our area, they lay eggs on cucurbits, which hatch, go through several larval stages, pupate in the plants’ leaves or in the leaf litter, and become adults in less than a month! This short life cycle means we may see two or even three generations of pickleworms a year.

Damage

The larvae can feed on flowers, leaves, and vines, as well as fruits. Larvae eating blooms can prevent fruit set. Like squash borers (Melittia cucurbitae), in the worst-case scenario, pickleworm larvae feeding on the vines can kill your plants. You may see pickleworm excrement (frass), or simply small holes in your fruits. In both cases, your crop is ruined once the larvae are feeding because the damaged areas with start to rot. According to University of Florida’s John L. Capinera, cantaloupes, with their thick skins, may have external damage called “rindworm.”

Pickleworm Larvae and Damage to Squash

Management

  • Early planting. Plantings that mature before the moths arrive are likely to escape pickleworm damage.
  • Resistant varieties. Some squash varieties that are more resistant: summer squashes Early Prolific Straightneck, Early Yellow Summer Crookneck, and Summer Crookneck; and Butternut 23 winter squash.
  • Floating row covers. Using row covers at night can prevent the night-flying moths from egg-laying, while still allowing pollinators to visit the flowers by day.
  • Garden clean-up. Removing damaged fruits and vines can prevent further generations in the same gardening season.

Learn more:

Pickleworm, University of Tennessee Publication # W206:

https://extension.tennessee.edu/publications/Documents/W206.pdf

University of Florida Featured Creatures:

https://entnemdept.ifas.ufl.edu/creatures/veg/pickleworm.htm

Insect Management on Cucurbit Vegetables in North Carolina

https://entomology.ces.ncsu.edu/cucurbit-insect-management-in-north-carolina/

Contact Us

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

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