A lilac branch that wilts while the rest of the shrub stays green, or bark crusted with tiny gray bumps, means an insect is at work. Borers, scale and leafminers are the lilac pests that leave these marks, and each shows up in its own season. Spotting the sign early helps you decide where to inspect and what to remove.
Which Insects Damage Lilacs?
In Maryland, lilac borers can cause serious damage. It is a wasp-like moth whose larvae tunnel inside the wood; in Maryland, heavy infestations may kill plants. Scale insects feed on the bark, and leafmining moths work inside the leaves.
What varies is mostly timing. Moths emerge in mid-May in Maryland and late May in Connecticut, while in northern Utah adults are active late April through late July. Late lilac may be attacked by the borer, and Manchurian lilac can be troubled by leafminers, thrips and willow scale in North Carolina.
The state selector just below this section leads to the page for your state, where the months for your area are laid out.
From the almanac
Lilacs in your state
The dates on this page depend on where you live. Your state's page carries its frost dates, its USDA zones and the year laid out month by month.
Northeast
Southeast
- Alabama
- Arkansas
- Delaware
- Florida
- Georgia
- Kentucky
- Louisiana
- Maryland
- Mississippi
- North Carolina
- South Carolina
- Tennessee
- Virginia
- West Virginia
Midwest
Southwest
West
Pacific Northwest
Canada
How to Find and Control Lilac Pests
Lilac pests arrive in a rough order through the year, so the gestures below follow the same order.
- Look over the bark in spring, so that scale is caught while the nymphs are emerging to feed, as they do in Wisconsin. In Kentucky, oystershell scale looks like crusty bumps of oyster shell, each about 1/10 inch long.
- Check the leaves for blotchy, tunneled patches so leafminer damage is spotted early.
- In Montana, watch for wasp-like moths in late spring, when egg laying on trunks and branches begins.
- Inspect the trunk base, from the soil line up to 3 feet, since in Iowa most borer infestations sit low on the plant.
- Cut out wilting or heavily infested stems and destroy them, so that larvae do not finish developing in wood left lying around the yard.
- Thin out 1/3 of the oldest branches to the ground each year, as Montana guidance suggests, so that the clump renews itself instead of aging into rough, wounded wood.
In Montana, preventing borers is the recommended way to control them, which is why the early checks matter. In North Carolina, late summer is another time to look. In North Carolina, adults emerge in August and September and lay eggs on rough bark or wounds.
Lilac Pests by Lilac Type
Pest checks vary somewhat by lilac type. A few types, though, come with their own notes, and those notes change where you look first.
Borer moths lay eggs on lilac trunks and branches, while leaf and bark pests vary by type. Leaf and bark pests are where types begin to differ.
| Lilac Type | What changes | Why it matters |
|---|---|---|
| Late lilac | May be attacked by the lilac borer | Trunk base checks come first |
| Manchurian lilac | Leafmining moth, thrips and willow scale may be problematic (North Carolina) | Leaves and bark need as much attention as the trunk |
For the lilac you actually have, the practical change is where to start. With a late lilac, begin at the base of the trunk. With a Manchurian lilac, look at the foliage and twigs as well. For other lilacs, use your state page to plan inspections around local pest activity.
Lilac Pest Control Mistakes to Avoid
Pruning While Moths Fly
Adult moths are drawn to fresh cuts as places to lay eggs. A pruning session during flight time can hand them exactly what they are looking for.
Wait until the moths have finished flying in your area, then make the cuts. The months differ by state, so the moth dates matter more than the calendar on the wall.
Trimming Only the Wilted Tip
Larvae tunnel in the solid wood and sometimes the pith for 8 to 10 inches, so a cut at the wilted tip can leave them behind. The damage then continues below the cut.
Cut well below the wilting, into clean wood, and destroy what you remove. In Florida, severely infested branches may break off if they are left in place.
Waiting for Damage to Show
By the time a branch wilts, the larvae have been feeding inside for a while. In Utah, a single female can lay about 400 eggs, so adult sightings deserve attention.
Watch for adults instead. In Montana, insecticides are applied two to three weeks after the first adult moths are captured to disrupt egg laying. Ask your local extension office what is approved in your state.
Lilac Pests in Your State
The sign that calls for action is a branch wilting low on the shrub while its neighbors stay green, often with rough, wounded bark nearby. Moth flight and scale emergence fall in different months from state to state, and the months for each state are on the page for that state.
- Go to your state page before pruning, to find when moths are likely to be flying.
- Use your state page to time the bark check for scale.
- In North Carolina, visit again in August and September, when egg laying on rough bark begins.
Common Questions
What Does a Lilac Borer Larva Look Like?
In Utah, full-grown larvae are described as about 1-inch-long with a white body and a brown head. Look for them when you cut into a wilted stem.
Do Lilac Borers Also Attack Privet?
In North Carolina, females lay eggs on the rough bark or wounds of lilac and privet. A privet hedge near your lilacs deserves the same checks.
How Soon Do Borer Moths Mate After Emerging?
In Utah, females emit a pheromone that attracts males within 7 to 14 days after emergence. Egg laying follows soon after, which is why the first moth sightings are the signal to act.