Invasive Insect Update

Mary Ann Ryan
Adams County Master Gardener Coordinator

(3/2017) Insects. Just the word can make some people’s skin crawl. "Over 900 thousand different kinds of living insects are known...and in the United States the number of described species is approximately 91,000." That’s a lot of bugs! However, of these many species, very few, less than 1%, are actually pests.

True pests in our landscapes may include insects like Japanese beetles, bagworms, and aphids. Most of which can be easily maintained with mechanical control like hand picking, or soft pesticides like insecticidal soap or summer oil. However, some pests can be deadly to our trees or shrubs and gardeners, homeowners and property managers should be on alert.

One such insect is the Emerald Ash Borer. This small borer is rarely seen, but the damage it leaves behind is very evident. It specifically targets ash trees, and this time of the year, when the leaves are off the trees, the damage is very apparent. Typically, woodpeckers make the D-shaped exit holes of the adult beetle even larger, as they go after the larvae for food, and the bark almost looks like it’s shedding due to woodpecker damage.

In PA, Emerald Ash was first discovered in the western part of the state back in 2007. In Adams and York Counties it was confirmed in the summer of 2014 and July, 2012 in Franklin County. Emerald Ash Borer (EAB) has been in Maryland at least since 2008. Quarantines have been set for the state of PA and MD, which limits any firewood that is moved across state lines. Unfortunately, this insect will destroy the ash trees in the forests and landscapes. If found on your property, the best measure of control is to cut the tree down and burn the wood.

If there are valuable ash trees on your property that are worth saving, there are pesticides that can be used prior to infection. The use of a systemic insecticide is the most effective way of controlling these insects before they attack a tree. Imidacloprid is a common active ingredient that is available to homeowners. It may be a good idea to contact an arborist to apply the insecticide, and they typically have more options as well.

A newer threat in our forests and landscapes is Thousand Canker Disease. As the name suggests, small lesions, or cankers, form under the bark, reducing the flow of water and nutrients up and down through the tree. This disease involves the walnut twig beetle as well as a fungus. The beetles carry the fungus and bore into the tree, thereby infecting the tree. Small cankers form where the beetles tunnel. Over time, the walnut tree declines, eventually to its death. Early symptoms include yellowing leaves and opening of the canopy. Eventually, large limbs will die and not soon after the entire tree will die too.

Unfortunately, there is little control for this disease and insect. Management for this disease involves removal of the infected tree. A quarantine has been placed on Bucks and Chester counties as well as Delaware, Montgomery and Philadelphia counties. "The quarantine restricts the movement of all walnut material including nursery stock, budwood, scionwood, green lumber and firewood. It also covers other walnut material living, dead, cut or fallen including stumps, roots, branches, mulch and composted and uncomposted chips. Due to the difficulty in distinguishing between species of hardwood firewood, all hardwood firewood is considered quarantined.

The quarantine also restricts the movement of walnut material and hardwood firewood from states known to have Thousand Cankers Disease including Arizona, California, Colorado, Idaho, Indiana, Maryland, Nevada, New Mexico, North Carolina, Ohio, Oregon, Tennessee, Utah, Virginia and Washington.

Non-compliance with the quarantine order could result in criminal penalties of up to 90 days imprisonment and a fine of up to $300 per violation, or a civil penalty of up to $20,000 per violation."

Spotted Laternfly is the most recent pest of concern. This spotted moth with orange/red coloration "has the potential to impact the green industry, grape growers, tree fruit growers, and the forest- and wood-products industries in Pennsylvania as well as throughout the United States."

It has one generation per year, overwintering in the egg stage. The eggs hatch in late April/early May, as many as 50 – 60 per egg mass. They go through four nymph stages before becoming adults in July. At the present time, they have been found in the western part of PA. Visit for more information on the quarantine.

The Viburnum Leaf Beetle is a concern for our native viburnums as well as the non-native viburnum species. There is one life cycle per year. Both the larvae and adult will feed on the viburnum leaves, skeletonizing the leaves and after feeding on the plant for a few years, the plant will die. Damage will appear as early as June.

Initially found in New York and Maine, the insect has been working its way south into northern and central PA. At this time, it has not yet been detected in south central PA. However, when it does reach this part of the state, there is control for the home gardener.

Take a look at the twigs of the viburnums in late winter - early spring. The insect overwinters as eggs and these masses can be seen as swellings along the twigs. When seen, prune them out and destroy the egg masses. Continue to monitor the plant during the spring for any feeding on the leaves. If spotted, spray with acephate, carbaryl, cyfluthrin, imidacloprid, or malathion in May to control the larvae.

Among some of the insects that have not yet reached this part of the state, but potentially pose a threat, is the Asian Long horned beetle. This insect was initially found in New York and is now also infecting Massachusetts and Ohio. There are regulatory and control actions in these states.

This insect is a boring insect as they work by tunneling into trees and girdling them, and they affect many tree species. Symptoms include yellowing leaves, reduced crown cover, branch dieback and eventually death. They create distinctive round exit holes. This beetle has not yet been found in PA, but there are a few look alikes that are often mistaken for an Asian Longhorned Beetle. If ever there is a beetle in question, take the sample to your local extension office for identification.

We will always have pests in our forests and landscapes. The hope is that we can manage them to reduce economic and environmental damage. The best way we can do this is by being informed and asking questions. Your local extension office is a wealth of information. Extension offices across the state have contact information to get you to the folks that know, and often times, have the answers without searching any further. Call, stop by or email us with your questions. We’ll find the answers. Our office is located at 670 Old Harrisburg Road, Gettysburg. PA 17325, 717-334-6271, email at In Maryland, call 301-600-1596, stop by at 330 Montevue Lane, Frederick, MD 21702, or visit us on line at:

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