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10 Tough Ornamental Pests

By Ron Hall


If we were to create a "10 Most Wanted" list of ornamental pests, we would be hard-pressed to find 10 more notorious and destructive pests than the ones you will be reading in this article. In all, more than 1,200 different feeding insects are known to attack the ornamental plants on your clients' properties. The 10 listed below are obviously just some of the more common ones you are likely to encounter.

OK, here goes. We'll count down alphabetically, which is no indication of their respective destructiveness given that some of these pests pick their targets more selectively than others. And some, such as the Japanese beetle, seem to have an appetite for just about anything in a landscape that is green.

1. Aphids - Aphids suck out plant juices or the succulent parts of plants. Their feeding causes distorted growth and wilting. You will find them on euonymous, violets, gardenia, willows, sycamores and hydrangeas especially.

2. Black vine weevils - These pests do their damage as larvae by feeding on the roots of plants. If the roots of a distressed plant are stripped or show notches, it's time to start looking for these critters. Among their approximately 80 favorite plant species, they seem to prefer yew, rhododendron, azalea and hemlock.

3. Bronze birch borer - It is often suspected when infected trees form swollen areas to heal infected areas that the Bronze birch borer is to blame. This diagnosis can be confirmed by finding irregular, winding sawdust-packed tunnels and small D-shaped holes. These pests attach white and yellow birches, aspen, willow and cottonwood.

4. Dogwood borers - Dogwood borers feed on the cambium and inner bark of limbs and trunks. Look for peeling bark, then dieback and adventitious growth. This serious pest typically feeds on flowering dogwoods, oak, willow, chestnut and hickory.

5. Eastern tent caterpillars - These pests build triangular silken nets in the crotch of tree limbs. You will find them on wild black cherry, birch, plum, apple, maple, oak and willow.

6. Elm leaf beetles - Elm leaf beetles skeletonize leaf bottoms and cause premature leaf drop. Small circular holes caused by adults feeding on trees. Their presence is generally indicated by the small circular holes on trees. They attack elm in all locales.



The Eastern tent caterpillar builds triangular nests in the crotch of tree limbs.
Photos courtesy Steven Katovich, USDA Forest Service, Bugwood.org. Poster image courtesy of Getty Images/iStockphoto.

7. Emerald ash borer - EAB arrived in the United States in southeast Michigan in 2002, and has since spread into eastern Canada and through much of the U.S. Midwest and Northeast. Its larvae feed on the inner bark of ash trees, disrupting the tree's ability to transport water and nutrients. To date, it has killed tens of millions of ash trees, and it continues to extend its range.

8. Euonymous scales - This pest typically reveals itself by the yellow spotting it creates on leaves. Euonymous scales may cover the stems of a plant so completely that whole branches or, in extreme cases, the plant dies. As hosts they prefer euonymous, camelia, holly and pachysandra.

9. Fall webworms - Fall web- worms are a cosmetic nuisance. If an outbreak is severe it can cause defoliation. It's most commonly found in birch, crabapple, linden, oak, popler, sycamore, willows and roses.

10. Japanese beetles - Japanese beetles feed on the tissue between veins of leaves. The damage they do is apparent as they leave behind lacy skeletons where green, full leaves formerly grew. Japanese beetles are somewhat non-discriminant when it comes to their food supply. While they particularly like trees and shrubs with delicate veins, they'll whatever else is handy if the opportunity presents itself.

Ron Hall is editor in chief of Turf magazine. Information courtesy Dow AgroSciences.