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Invasive Invaders
by Pamela J. Bennett - posted 04/18/12

Many species of non-native invasive plants, insects and animals plague the Midwest. Why should gardeners care? Here is what you need to know.

Tartarian honeysuckle.

Chestnut blight in the early 1900s. Dutch elm disease in the mid-1900s. Emerald ash borer in the early 2000s. Asian longhorned beetle has been discovered in five states with the most recent find in Ohio. The list of invasive species goes on and grows.

I don’t remember when the first two devastating invasive species hit the news but my dad tells me stories of giant elm trees in front of their house being removed. Unfortunately, today, I am living in the time when scientists suggest that we might be looking at possibly the most damaging invasive pest of our time, worse than any of the above — the Asian longhorned beetle.

An invasive species is one that grows outside of its native or normal range, spreads rapidly in unwanted areas and flourishes to the detriment of other species. They are often human-introduced. The U.S. Department of Agriculture defines an invasive species as a non-native species (or alien) to the ecosystem under consideration and whose introduction causes or is likely to cause economic or environmental harm or harm to human health. While gardeners tend to focus on invasive plants and plant pests, there are other invasive species such as zebra mussels and other animals of which we should be aware.

Why Care About Invasives?

Garlic mustard in its second year in bloom — note the tall white flowers in the background.

Amur honeysuckle fruit.

Many people don’t tend to give thought to invasive species until they are directly affected by them. For instance, woodland owners are quite aware of honeysuckle and garlic mustard problems, but most gardeners don’t deal with these in their home landscape. However, I have seen both of these species creep into landscapes unnoticed. Today, we are seeing two extremely damaging species in particular taking out our urban forest, emerald ash borer and Asian longhorned beetle. My goal is to get the word out and raise public awareness regarding invasive species.

According to Kathy Smith, Ohio State University Extension forestry specialist, we are seeing non-native plants invading forests with the potential to drastically change the forest ecosystem. Many of these species are not as nutritionally valuable to animals as the native plants. The loss of species to these invaders will also change the products that these forests produce.

Smith goes on to say, “While there have been non-native species in the past, none have seemed to move in with the aggressiveness that this current cadre seem to do. On the insect side, 12 percent of Ohio’s forests are ash and will be lost to emerald ash borer. While 50 percent of Ohio’s forests were American chestnut at one time (and lost to chestnut blight), there was not the invasive plant aspect that makes this almost a one-two punch.”

For example, when the forest canopy opens up due to dead and dying trees, the possibility for seeds from invasive species such as Ailanthus sp., honeysuckle and autumn olive to get a foothold increases. Without a management plan for these species, they end up outcompeting the native tree and shrub species in the forest ecosystem. This leads to a changing forest for our wildlife species and impacts the forest products that can be harvested along with many of the other intrinsic values we depend on the forests to provide.

Economic Impacts of Invasives

Amy Stone, emerald ash borer outreach specialist for OSUE, points out that the ecological and economic impacts from invasive species such as emerald ash borer and Asian longhorned beetle are enormous. The long-term impact, including the management of invasive plants that often come in after trees die can be a long battle that includes increasing costs each year. The individual cost to homeowners to remove dead trees in the urban landscape as well as replace them is high.

Invasive species can be quite costly, both in their impact and removal. A University of Wyoming study noted a $200 million impact in the Great Lakes region by invasive species brought in on ships. These losses are to commercial fishing, sport fishing and the area’s water supply. As of 2008, total state and federal costs for Asian longhorned beetle eradication alone added up to around $373 million.

What Can Gardeners Do?

As gardeners and people who care for the environment, we need to get everyone thinking about invasive species and their influence. Be on the lookout for anything unusual, odd, different, or problem-causing. The sooner an invasive species is discovered in an area, the lower the potential for economic and environmental impact. Eradication efforts can begin at an early stage rather than after the species has become entrenched in the area.

Share invasive species information with friends, family and others. Moving firewood is one of the easiest methods of moving emerald ash borer and Asian longhorned beetle in an area. Don’t take firewood when you go camping. Purchase it locally. Point out garlic mustard to your friends while hiking through a natural area. Get involved in invasive species plant eradication efforts in your state.

Learn all you can on the topic of invasive species and spread the word quickly! An educated public that can recognize the importance of reporting unusual or unfamiliar insects or other pest activity is critical to early detection. Become “invasive” yourself by telling others — get all eyes on the ground and in the trees monitoring for any potential invasive pests. We are only going to see more instances of invasive species in the future; take action to protect our natural environment.


Asian longhorned beetle exit holes in the bark of a tree. Inset: Adult Asian longhorned beetle.

Asian Longhorned Beetle

The Asian longhorned beetle has been pegged by scientists as potentially the most damaging pest in the United States. It was first discovered in Chicago and has since been eradicated there. However, there are outbreaks in New Jersey, New York, Massachusetts and most recently Ohio. This beetle has a wide taste for trees (primarily maple but also elm, hackberry, horsechestnut, London planetree, poplars and willow) and kills them completely.

The adult beetle is approximately 1 to 1½ inches long with a shiny black body and distinctive spots and long antennae banded with black and white coloration. The larvae are also quite large and create a dime-sized exit hole in the trunk of the tree.

The beetle spends most of its life as a larva inside the tree, feeding on tissue directly beneath the bark when it first hatches. Eventually it begins to burrow deep into the tree, feeding on woody tissue. It pupates inside the tree and emerges as an adult in July and August. The adults feed on twigs, mate and lay eggs. They tend to lay eggs on the same tree every year until the tree dies.

Be on the lookout in your neighborhood, parks and natural areas for trees with:

• Shallow depressions in the bark where the beetle lays the eggs

• Dime-sized exit holes where the adult beetle emerges

• Sawdust-like material, called frass, on the ground and branches

• Dead branches and canopy dieback

• Also watch for the adult beetles as they can be seen on trees, branches, walls, outdoor furniture, cars and sidewalks.

• Go to for photos, details, and who to contact in your state if you suspect the Asian longhorned beetle in trees.


(From State-by-State Gardening January/February 2012. Photos courtesy of Pamela J. Bennett.)   


Pamela J. Bennett is the state Master Gardener volunteer coordinator and horticulture educator for Ohio State University Extension.