Guarding the Landscape

Strategies for controlling common outdoor pests

By Rob Duca | Pictured above:Fall cankerworm / Photo Tim Tigner, Virginia Department of Forestry, Bugwood.org

They are called pests for a reason. They are a nuisance, a constant irritant, and seem perpetually intent on destroying your landscape. They defoliate your trees and turn the leaves yellow, brown or black. They wreak havoc on your azaleas and rhododendrons.

And then there were this year’s scourge, the ever-present gypsy moth caterpillars, hanging on trees, covering decks and leaving a mess in their wake.

What to do?

“It all starts with monitoring,” says Natascha Bachelor of Davey Tree Service in East Falmouth, Massachusetts. “Not all pests are everywhere all the time. I encourage clients that if they see something they haven’t seen before, give us a call and we’ll come out and offer advice.”

Gypsy moth caterpillar larvae | Photo USDA APHIS PPQ, Bugwood.org

There wasn’t much to be done about the gypsy moth caterpillars this year. They simply had to run their course. But prevention is vital in protecting your trees, shrubs and plants from many common yard pests, and in most cases homeowners can apply treatments without the need to hire a professional.

“But it’s very important that you read and follow the label,” Bachelor says. “If it’s too hot or the treatment is over-applied, you can burn the plants.”

Normally, gypsy moth caterpillars are kept in check by a fungus, but that fungus requires moisture to survive and do its job. “We had a drought over the past two years, so the fungus didn’t have enough moisture and the gypsy moths got out of control,” Bachelor says. “It’s hard to say what next year will be like until we see how many survived.”

Taming tree raiders

One pest that can be controlled is cankerworms, which eat away at leaves, stripping the tree of nutrients. They usually attack elm, oak, apple, maple, linden, beech, cherry, hickory and ash trees, leaving chewed, ragged-looking leaves that fall prematurely in the spring. It is important to apply a pesticide in the spring, and then follow it with an insecticidal tree band in the fall.

The Eastern tent caterpillar leaves large, silky spider webs, especially on black cherry trees. They also affect ash, birch, sweetgum, willow, maple and oak trees. With these caterpillars, you should first clip and destroy the tents, but wait until winter to remove the silky webs. A professional can then apply a treatment to control the larvae.

Rhododendron lace bug infestation | Photo Jim Baker, North Carolina State University, Bugwood.org

Managing pesky plant-eaters

If you detect leaves curling, a sugary substance called “honeydew,” a black, sooty mold and stunted growth, the villain is plant lice, which feeds on tree leaves and stems. Plant lice can be stopped with horticultural soap treatments or insecticides.

A reddish-orange color on the undersides of the leaves on your trees and shrubs is a good sign that you are dealing with lace bugs. They are particularly drawn to azaleas and rhododendrons, and will also make leaves appear yellow and bleached out.

“Those plants want to be in the shade, but many people plant them in full sun, and that attracts the lace bugs,” Bachelor says. “A mild insecticide will work. Spray it on the underside of the leaves.”

It’s best to use insecticidal soap, neem oil or narrow-range oil. A broad-spectrum insecticide will destroy the lace bug’s predators, which could lead to a spider mite problem. One method of natural control is to work compost into the soil and mulch around the plants to keep the soil evenly moist, because lace bugs prefer hot, dry and sunny environments. Although the damage won’t disappear, the plant will return the following spring with healthy leaves.

Lace bugs have two seasons. Therefore, it’s important to apply treatments between mid-May and early June, and a second time between mid-July and early August. “Repeated treatments depend on the intensity of the population,” Bachelor says.

Oak lace bug | Photo USDA Forest Service, Northeastern Area , USDA Forest Service, Bugwood.org

Plants that turn black are the result of scale bugs, which are small, oval and flat, with a protective tan to brown shell-like covering. They generally target the undersides of leaves and around leaf joints. “As it sucks the sap out of the plant it takes the sugar, which runs onto the leaves and leaves a mold that causes that black color,” Bachelor says. “It’s really quite striking.”

Bachelor recommends using horticultural oil to rid scales, which usually affect varieties of holly plants.

Regulating mighty mites

Finally, there are mites, which are difficult to monitor because they can’t clearly be seen without magnification. Some mites produce webbing and cause discoloration of leaves that eventually leaf drop. They are most likely to affect hemlocks and spruce trees. “If the foliage gets a rusty brown color, then you’ve probably got mites,” Bachelor says.

Horticultural oil is the preferred treatment, and, in this case, Bachelor recommends hiring a professional. “Mites reproduce in high heat every eight days, so a rotation of treatments is very important,” she says.

Left unchecked, all these pests can turn your landscape into a liability. But with careful monitoring and treatment, you’ll be able to enjoy your beautiful trees, shrubs and plants year after year.

Eastern tent caterpillar | Photo Pennsylvania Department of Conservation and Natural Resources – Forestry, Bugwood.org

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