Cold season activities to manage tree & shrub insect pests

While many management activities for insect pests of trees and shrubs end when the frost arrives (like most, if not all, insecticide treatments), some are still applicable in the cold winter months. Examples include:

• Scout for egg masses and act accordingly. Many (not all!) insect pests overwinter as egg masses either on host plants, nearby or on any manner of surfaces (depending on the species). Finding them at this stage is a great opportunity for mechanical management.

Egg masses can be scraped, rubbed or pruned from trees and shrubs and disposed of. Examples include but are not limited to:

1. Eastern tent caterpillar or forest tent caterpillar – Both native insects lay similar (but slightly different) egg masses near the ends of the twigs of their host plants. In forests, these egg masses can be left alone as these insects are important in our ecosystems. On ornamental trees and shrubs, particularly crabapples, apples, flowering cherry, etc., these egg masses can be pruned out and removed to reduce insect pressure and pesticide use in spring. On those hosts, the egg masses likely belong to eastern tent caterpillar.

On birch, elm, hawthorn, poplar and willow the egg masses could belong to the forest tent caterpillar.

2. Bagworm – Caterpillar females die in the bag they create around themselves, typically after laying their eggs. Eggs overwinter within the bag. While older bagworm bags can remain tethered tightly to branches for years (and may no longer have viable eggs within), this season’s may contain 500 – 1,000 overwintering eggs. Remove and destroy any that are found on arborvitae, juniper, oak, London planetree and other hosts.

3. Spotted lanternfly (SLF) – SLF adults have mated and the females have laid their eggs on a wide array of surfaces (host plants, downed debris, outdoor furniture, play equipment, fences, guardrails, tires, lightbulbs, etc.). Egg masses can be scraped from these locations or the eggs within popped to kill some of the insects. Just remember that what you see is the tip of the iceberg. The vast majority of SLF eggs are high up in the canopy. SLF is not native to the Northeast.

Report any life stages (adults, eggs or nymphs) to your state department of environmental conservation.

• Pruning out dead branches. If insects, other pests, diseases or environmental factors have caused branch dieback, winter can be a great time to start pruning. During the warmer months, pruning cuts can be attractive to wood-boring insect pests. It may even draw them to the tree or shrub or create a more favorable location for them to lay their eggs (depending upon the species). Saving this activity for the cold months can avoid the accidental attraction of more primary (the cause of the dieback) or secondary (not the original pest to cause the dieback, but one that will benefit from it) pests.

• Scout for problems that might arise next year.

Boxwood leafminer symptoms, for example, may be obvious in winter. While chemical management is not possible now, make notes of which plants/properties may need attention next year. Hemlock woolly adelgid will be visible in their white woolly ovisacs in the cold months, including November through March, and doing most of their feeding over winter. Winter mortality of this insect often occurs but note sizeable populations to plan scouting again as spring temperatures warm. Check the viability of the population next season to determine if management is necessary.

While the leaves are off the trees, monitor for issues with wood-boring insects that may be obvious now that they are not obscured. Did that ash tree have leaves on it this year? How much of the bark has been removed by hungry woodpeckers feasting on emerald ash borer larvae? Consider if it’s time to evaluate the tree for hazard status. Can it be treated next year or does it need to be removed?

• Persistent soft scale issues? Have you had issues with tuliptree, magnolia, fletcher, lecanium and other soft scales? Many of these species overwinter as small, relatively flat, second instar or other instar nymphs (immatures) on the twigs of their hosts. Grab some magnification and have a look at smaller twigs and branches. Does it look like you might have a population issue to monitor next year?

• Monitor for armored scales. Check trees and shrubs for the presence of armored scale buildup on smaller branches and twigs and needles. Start with lower branches and work your way up. Some may also be present on tree trunks. Scouting for euonymus, elongate hemlock, pine needle, juniper, oystershell and other armored scales in winter can aid in making plans for spring.

• Look for old evidence of lace bugs. Hosts that hold their leaves such as evergreen azaleas may retain stippling (white or chlorotic spots on the upper surface of the leaves) and may be noticed at this time. While you cannot treat lace bugs at this time of year, make a note to monitor the plant(s) throughout the growing season in 2026 and determine if lace bugs are present, continuing to cause unacceptable injury and need management attention.

by Tawny Simisky, UMass Extension Woody Plant Entomologist