What happens to all those pesky summer insects when temperatures drop? While some die off and others migrate, most take refuge underground or in our trees, entering their own state of dormancy for the winter.
Not all overwintering insects harm plants and soil. In fact, many pollinators emerge in the spring to support newly blooming flowers. While common Maryland tree pests such as scale insects and bagworms remain dormant during the winter, they overwinter on trees and become active as temperatures warm. Without proactive management, these pests can quickly cause damage in the spring and summer, sometimes before trees have a chance to recover.
Recognizing the signs of overwintering pests can help you protect your trees from these seasonal threats. This guide covers everything you need to know, including the most common pests in Western Maryland, signs of tree damage, and how our tree care team can help you stop the infestation.
Why Do Pests Overwinter?
Like other wildlife, insects must seek shelter and adapt to survive the winter. During the overwintering stage, many enter diapause, a developmental pause characterized by reduced or no feeding or movement. In some respects, diapause is similar to hibernation; insects preserve themselves until the weather is warmer.
Before or as temperatures drop, tree pests will locate a host tree and attach themselves in preparation for diapause. Each species shelters in a slightly different way—through bark crevices or through the soil surrounding a tree, for example. Below, we’ll review a few of the most common overwintering pests in Maryland and how they target trees for winter shelter.
4 Common Overwintering Pests in Maryland Trees
The vulnerability of your trees depends on your exact location, the tree species and health, seasonal conditions, and, of course, the presence of pests. Here, we’ll introduce four common insects that seek out winter shelter in Maryland trees.
Emerald Ash Borer
Emerald Ash Borer (often referred to as EAB) is an invasive species that has killed millions of ash trees in the Midwest and eastern United States. After hatching, EAB larvae tunnel beneath the bark and feed on the tree’s inner tissue, disrupting its ability to transport water and nutrients. They develop under the bark over the winter and, from late spring through summer, emerge as adult beetles, leaving behind small, D-shaped exit holes.
Bagworms
Bagworm moths get their name from the tiny, bag-like structures their larvae create and carry while feeding on tree foliage. After mating, female moths lay up to a thousand eggs in their cocoons before dying. The eggs remain during the winter and hatch when the weather warms in spring.
Considered to be caterpillars in this stage of life, bagworms do not stay in one place on the tree. They move between leaves and trees to feed, carrying their bags. In early warm-weather months, damage to infested trees may not be noticeable. But over time, sometimes by late summer, a decline in tree health and even tree death can occur.
Bagworms do the greatest damage to conifer trees (pines, cedars, etc.), although you may also find them on deciduous trees.
Scale Insects
There are two key types of scale insects: hard, armored scale and soft scale. You can usually distinguish between the two by appearance: the soft scale has a flexible, waxy exterior, and the armored scale has a shell-like outer layer. Also, only soft scale excrete honeydew residue when they feed on trees.
These insects suck plant sap using their unique piercing mouths. A large infestation can severely weaken plants and trees. The honeydew may also develop mold over time, causing further damage.
Aphids
Aphids are small, pear-shaped insects recognizable by their long legs, antennae, and horn-like cornicles on their back sides. They can be green, yellow, white, or other colors, depending on the species. While aphids are considered pests, they don’t cause the same degree of damage as EAB or bagworms. Similar to scales, they feed on plant sap and excrete honeydew residue. They can also carry and spread diseases that damage trees.
The Signs of Overwintering Pests in Your Trees
These insects, along with their effect on host trees, are sometimes difficult to identify without familiarity. Be on the lookout for these warning signs:
- Egg masses attached to bark, branches, or needles
- Bag-like structures or cocoons remaining on branches (such as bagworms)
- Unusual growths, including silk-like webs or protective coverings
- Small exit holes in the bark from pests that emerged the previous season
- Larvae, cases, or other insect structures tucked into bark crevices or branch unions
If you suspect pests or your tree’s health is declining, do not wait to schedule an inspection with a specialist. Early detection of pests and diseases increases the likelihood of tree recovery. Also, do not attempt to treat pests by yourself; only a professionally trained arborist should handle pesticide treatments.
How Tree Care Specialists Treat Overwintering Pests
ISA-certified arborists can accurately identify tree problems and present a treatment plan to restore your tree’s health. If overwintering pests are affecting only part of a tree, the tree care team may prune the damaged branches. Many arborists also use a dormant oil, also called winter wash, to kill and keep pests from laying eggs.
In severe cases of damage done by an infestation, tree removal may be the best option. Removing an infected or dying tree can prevent disease spread, preserve the health of surrounding trees, and help eliminate your pest problem.
Tree care experts can also recommend preventive measures, as a once-infested tree remains at risk of future pest damage. Some trees may require annual treatments to keep pests away, and regular monitoring and assessments will help you stay on top of warning signs.
Protect Your Trees From Maryland Pests With Baker Tree Services
The best time to address overwintering pests is before they emerge in the spring. Even if you haven’t noticed much of a change in your trees’ health and appearance, any sign of pests should be inspected and addressed immediately to prevent further damage.
With more than 20 years of experience serving our Western Maryland counties, Baker Tree Services provides expert pest and disease management services. Our ISA-Certified Arborists use proven, effective methods to combat overwintering pests and prevent disease spread.
We are committed to keeping your landscape healthy and thriving, no matter the season. To schedule an inspection, call 240-288-7223 or contact us online today.