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5 Invasive Species Delawareans Should Watch Out For

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Japanese Beetle

The Delaware Invasive Species Council has named August Tree Check Month, calling on tree owners to take notice of any suspicious activity, from beetle boring holes to fine fungi growth.


Since the dawn of the Industrial Revolution, innumerable invasive pests, including insects, have hitchhiked with shipping cargo across continents. This becomes a major problem when these foreign invaders who have made their way here (and America’s, elsewhere) have no predators and prey upon native plant species with no resistance to them. Over time, the damage can be deadly to trees and shrubs, and costly to those who own them. The Delaware Invasive Species Council has named August Tree Check Month, calling on tree owners to take notice of any suspicious activity, from beetle boring holes to fine fungi growth. Jason Gaskill, assistant district manager of Davey Tree Wilmington, shares five invaders that Delawareans should watch out for and what to do if you spot one.

Spotted Lanternfly

The Spotted Lanternfly (Lycorma delicatula) hails from eastern Asia and is abundant in August. Up to an inch long and half-inch wide, this bug is aptly named for its pretty spotted wings—so attractive to one artist that she captured and created jewelry with them. First identified in Berks County, Pennsylvania, in 2014, the fly caught the nickname “the hitchhiker bug” for rapidly laying eggs in the oddest of places—the grille of a car, under windshield wipers—and getting transported all over the place. Now spotted in New Jersey, Delaware, and parts of Virginia and Maryland, it populates in incontrollable numbers across maples, river birches, grapevines and other host species that can’t resist them. From early spring to late fall, check your vehicle for any signs of eggs, which can be scraped off and discarded in a plastic bag filled with alcohol to mitigate the spread. For trees already under duress, arborists can exterminate egg masses and spray or inject trees with a protectant that bids bye-bye to the lanternfly.


RELATED: Will the ‘Murder Hornet’ Make its Way to Delaware?


Emerald Ash Borer

About a half-inch in length, the metallic green Emerald Ash Borer beetle (Agrilus planipennis) emerges from ash trees sometime in June and buzzes about the summer. Native to Asia, the pest was first spotted in the U.S. in Detroit in 2002, where it traveled via shipping crates, but it’s estimated to have first arrived in the late 1990s. Once here, it migrated with folks moving firewood. Delaware’s ash trees have fallen victim to this “silent killer” for about four years. It lays eggs inside the bark, where larvae eat through the trees’ insides like Swiss cheese, cutting off nutrient flow. While the beetle itself spends most of its life inside a tree, its map of destruction is easy to identify. Dying from the crown down (since root nutrients can’t reach the top), trees become brittle and eventually hazardous. Arborists administer treatment like a shot, which travels into the tree, destroying predators.

Japanese Beetle

Migrating from Japan more than a century ago, the Japanese Beetle (Popillia japonica) was first discovered in a nursery and is thought to have sailed over with a shipment of bulbs. The size of a dime and arguably the most destructive garden pest, the intruder thrives in the heat of summer, feasting on a variety of trees and shrubs, from rose bushes to grapes and crepe myrtles. With no predators and defenseless hosts, the beetles swarm in. Pretty conspicuous in part due to their size—if you shake a branch, a bunch might fly out of the tree—their presence is also easy to spot by the skeletonized leaves they leave behind. Sporadic brown patches in your lawn may also be a sign of the beetle, known to feed on grass roots where it lays eggs. Systemic soil drenches and tree injections offer long-term control, but timing is important: They must be applied before the beetles become active in late June.

Hemlock Woolly

Spotted first in Virginia in 1951, the Asian-born Hemlock Woolly Adelgid (Adelges tsugae) can now be found from Maine to Georgia throughout the eastern range of hemlocks. In large numbers, these tiny puffball insects look like a dusting of snow across the hemlocks’ pyramidical, Christmas tree–like branches, where they feed on their sticky sap. Easy to control if you notice them early—in the right conditions, they can kill a tree in four to 10 years—the adelgid infestation is no match for an arborist.

Dogwood Anthracnose

Thriving in cool, wet weather typical of early spring and fall, Dogwood Anthracnose (Discula destructiva) is a grave threat to native dogwood trees. While the fungus’ origins are unknown, it was first detected here in the 1970s in the eastern U.S. and has since spread throughout the entire region. Signs of anthracnose appear as tan and reddish-purple legions on the trees’ lower leaves, which eventually curl and fall off. Having quality fertilizer and making sure dogwoods are well-watered can help fight disease. To prevent an infestation, have an arborist apply a fungicide in the springtime when foliage is tender and leaves are more susceptible to damage.

We can all benefit the environment by taking care of our own, Gaskill says. And what better time to tend to our trees when we’re all on lockdown and doing laps around our yards anyway?


Published as “Alien Invaders” in the August 2020 issue of Delaware Today magazine.

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