Five Pests You Need to Watch this Summer
Spring is a great time of the year. With life emerging from its long winter sleep, it’s among nature’s most active seasons. But spring is also a time when plant pests emerge. These pests can ravage your trees and kill them. Basically, you can divide tree pests into three broad categories—sap-sucking insects, wood borers, and defoliators.
Pests invade trees when they’re under great stress. Pests introduced from outside their native range can severely impact crops and natural tree populations, generating billions of dollars of economic and ecological damage. However, what insects you’ll need to watch out for this summer depends on your location.
Tree pests cause tremendous to natural and managed land annually. Most tree damage is caused by 20-22 common insect pests. These pests can devastate a tree if left untreated and cause extensive economic damage by destroying landscape trees that has to be removed and replaced. The impacts of pests are often made worse by climate change, which may allow additional pest life cycles per annum.
Not all pests are deadly, however. Some play critical roles in natural and managed systems, contributing to carbon cycling and forest regeneration. They may even contribute to shaping patterns of global tree diversity. Below are five pests to look out for and descriptions of telltale signs that they have invaded your trees:
1. Arborvitae leafminer
If you see brown foliage now on your “Green Giant” and “Emerald Green” cultivars, it’s a sign that these pests are feeding on your plant’s leaves. This leafminer pest is a small caterpillar, green or brownish, with a dark head and a spot just behind its head. Mature caterpillars generally appear between April and June. While this pest likes all arborvitae varieties, they prefer American pyramidal, globe, and golden arborvitae.
2. Cedar Rust
Cedar apple “rust” can affect the health and vigor of your apple trees by causing early defoliation and reducing fruit quality. They present as orange gelatinous spheres and indicate the presence of fungal spores from the Gymnosporangium family, which can later infect Malus species. Cedar rust is especially harmful to Junipers. Severe infections of this disease, which first appear on leaves as small greenish spots and then gradually enlarge and change color, can kill a tree.
3. Holly Leafminer
As the name suggests, it feeds on English, American, and Japanese hollies. If you see tiny green blisters on a lower leaf’s surface, chances are good the female of this pest has laid eggs there. The Holly leafminer “causes the presence of yellow, brown, or reddish mines on the leaves. In the beginning, the mines are narrow and winding. But they then become large blotches as the larvae overwinter in the leaf. The upper and lower surfaces of leaves remain after feeding and are easily separated. Larvae are yellowish and about 1/16″ long. The adult is a small black fly.
4. Boxwood Leafminer/Blight
These pests are among the most destructive—and deadly— of the boxwood insect pests. The larvae feed on the tissue between the leaves’ outer surfaces, producing blotch-shaped mines in the boxwood leaves. Circular leaf lesions are a crucial symptom of boxwood blight, as are leaf yellowing and leafminer injury blistering. Infested leaves appear blistered from late summer through the following spring. New leaves, however, don’t show signs of mining until deep into summer, when the larvae are larger. Premature leaf drops may result from heavy infestation by fall or early spring.
5. Pine Needle Blight
A common fungal disease among pines, especially mugho and Japanese white pines, pine needle blight attacks pine needles, causing spots, blights, and premature defoliation. Initially, spots emerge in summer or late fall. It’s a group of diseases. Cyclaneusma needle cast symptoms appear as light green to yellow spots on infected 2-year-old or older pine needles. Dothistroma needle blight causes yellow to tan spots in the fall. Lophodermium needle cast appears in late fall to early spring. It presents as brown spots with yellow margins on young needles. Brown bands form later.
These five pests are common in the Northeast. But don’t panic if you see one or more of them on a tree’s leaves or something foreign on its bark. Instead, get to work diagnosing the problem and deciding on the best treatment for the pest. Treatment for these pests, however, varies. So, if you need help treating them, contact the RI Tree Council as soon as possible. We’ll help you eliminate these pests and boost your tree’s health.
John Campanini is technical director of the Rhode Island Tree Council (RITree). A graduate of the University of Rhode Island, he was city forester for Providence for more than twenty years before retiring.