The beetle behind most plumeria borer damage is only about half an inch long. Its grubs, though, do their work out of sight inside the wood, which is why a plumeria borer problem often shows up late. By the time a branch wilts or snaps, the tunnels are already there.
This guide covers which borers attack plumeria, the signs to look for, and how to tell borers from rot or cold damage. It also covers what actually helps once a grub is inside a branch. We’ll be honest about where the research is thin, because for plumeria it still is.
Which beetle is the plumeria borer?
The insect most growers mean is the plumeria longhorn borer, Lagocheirus obsoletus. It is also listed under the name Lagocheirus undatus. A 2019 Hawaii study calls it a pest of plumeria and other ornamental plants that feeds on many host species.
The adult is mottled brown and stocky for a longhorn, with tiny spines on the thorax. The Big Island Invasive Species Committee describes it as about half an inch long. Plumeria is its main host, though it has also been recorded on cacao and kukui.
It is best documented in Hawaii, where it has become established on Hawaii Island. Catalogs also list the species from the southwestern United States, Mexico, Costa Rica, Cuba and Jamaica. How common it is on plumeria in Florida, Texas or Australia is not well documented, so we won’t claim a range we can’t verify.
Other wood boring insects can also tunnel into plumeria branches, and growers often cannot tell them apart without seeing the adult or grub. The signs and the fixes below apply to most of them. Only a specimen sent to a local extension office or pest agency will settle the exact species.
Signs of a plumeria borer problem
Borer damage is mostly hidden, so you are looking for clues on the outside of the branch. Longhorn grubs are beetle larvae. Beetle borers usually pack their waste inside the tunnel, so exit holes may only appear after the adults leave.
- Small round holes in the bark, especially near branch forks and the base of the trunk.
- Frass, which looks like fine sawdust or coarse granules, around a hole or on the leaves and soil below.
- Sap oozing from a hole, sometimes drying into a crust.
- Wilting or yellowing tips on one branch while the rest of the plant looks fine.
- Dieback that moves back from a branch tip.
- A branch that snaps in wind and shows a tunnel or hollow center at the break.
Plumeria is a succulent, fleshy plant with milky latex, so a tunnel can look different than in a hardwood tree. Cut a suspect branch open lengthwise if it is already dying. A tunnel packed with sawdust, or a pale fat grub, confirms a borer.
If you find the adult beetle, take a clear photo. In Hawaii, that committee accepts pest reports from residents. Elsewhere, your state or county extension office can help with identification.
Borer, rot or freeze damage: how to tell
Several stem problems look alike from a distance. A drooping, dying branch could be a borer, rot or cold injury. The inside of the stem and the pattern of the damage usually tell you which.
| Cause | What you see outside | What you find inside |
|---|---|---|
| Borer | Small holes, frass, one branch failing | Dry or packed tunnels, sometimes a grub |
| Rot | Soft, dark, sometimes smelly tissue, often from the base or a cut | Wet, mushy, discolored flesh with no tunnels |
| Freeze | Blackened, limp tips after a cold night | Water soaked or brown tissue, no holes or frass |
If the tissue is mushy and wet, read our guide to plumeria stem rot and the page on a soft plumeria stem. If a cold night came first, our page on plumeria freeze damage and pruning walks through the assessment. For a wider look at branch trouble, see plumeria stem and branch problems.
Borers and rot can also occur together. A tunnel lets water and fungi into the stem, and a rotting branch can attract insects. If you see holes and soft tissue, treat the borer first by removing the branch, then deal with any rot you find.
Why borers pick certain plants
Extension sources on borers in general say that stressed, wounded or neglected plants are the easiest targets. Drought, bark damage from mowers or string trimmers, and mulch piled against the stem all raise the risk. The same advice should hold for plumeria, though we found no plumeria specific study that tests it.
A healthy, well watered plant on a proper schedule is harder for a grub to take over. Our complete plumeria care guide covers the light, watering and feeding that keep growth strong. Dead stubs and old broken branches are also an invitation, so tidy them up.
Borer infested branch
Grubs live inside the wood, so the damaged branch has to be cut out below the tunnel.
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Cut into clean wood below the lowest hole with a sharp bypass pruner.
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How to control a plumeria borer
Once a grub is inside the wood, removing that wood is the dependable fix. Here are the steps growers and extension guides commonly follow.
- Find the full length of the damage by tapping or lightly cutting into the branch.
- Cut at least a few inches below the lowest hole or tunnel, into clean, solid tissue. Growers commonly cut until the inside looks healthy and white.
- Use clean, sharp tools and wipe the blades between cuts. A bypass pruner works for thin branches, and a pruning saw suits thicker wood.
- Do not leave the cuttings on the ground. Bag them, chip them small, or bin them so any grub or pupa inside cannot finish its life cycle.
- Check the cut face. If you still see a tunnel, cut again lower.
The Fiskars bypass pruner above suits branches up to its rated cutting size, according to the label. For thicker limbs, a folding pruning saw is easier on your hands, but neither tool kills the insect.
Plumeria sap is a skin and eye irritant, so wear gloves and eye protection. Our page on plumeria sap and toxicity has the details. Our pruning guide shows where to cut for good regrowth.
Should you seal the cut?
Growers disagree. Many plumeria growers dab sealant, fungicide powder or similar on large cut faces to keep rot and insects out. Tree research more generally has found that wound dressings do not speed healing and may trap moisture.
We found no study that tests wound sealing against plumeria borers specifically. A reasonable middle path is to make clean cuts, keep the cut face dry, and skip heavy coatings. If you do seal, use a thin layer after the latex has stopped running.
When to prune
If you have an active infestation, prune a dying branch right away. A grub can keep eating and spreading while you wait. A broken branch is also a hazard.
For routine pruning, timing may matter. The University of California pest guide for a different group of branch borers notes that adults fly in spring and advises avoiding fresh wounds then. The flight season of the plumeria borer is not well documented, so we can’t give you exact dates.
In most climates, growers prune plumeria in late winter or spring as the plant wakes up. The winter care guide explains the dormant season. If you see adult beetles around your trees, consider delaying elective cuts until they stop appearing.
Do sprays and insecticides work?
Honestly, not well. The University of Maryland Extension states that no conventional insecticides will kill borer larvae once they are inside branches. That matches the common grower experience with borer grubs in general.
Some extension guides mention beneficial nematodes squirted into active tunnels. They are labeled for other borers, and we found no test on plumeria. If you try them, follow the label and expect mixed results.
Spraying bark with a contact insecticide might reach adults walking on the surface. It does not touch grubs deep in the branch. Be careful with any product near flowers and pollinators, and always follow the label.
Keeping new borers out
- Remove dead stubs, broken limbs and fallen cuttings.
- Keep mulch a few inches back from the trunk.
- Avoid nicking bark with trimmers and mowers.
- Water and feed on a regular schedule.
- Look over branch forks every few weeks when the plant is growing.
When to call an arborist
A potted plumeria is easy to inspect and cut yourself. A mature plumeria tree in the ground is harder. Call a certified arborist if the trunk itself is tunneled, if several large limbs are affected, or if a heavy branch hangs over a house, path or car.
An arborist can judge whether a tree can be saved and can remove weakened limbs safely. In places where the plumeria borer is a regulated or tracked pest, such as Hawaii, ask your local extension office or pest committee for the right way to dispose of infested wood.
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Frequently Asked Questions
Can a plumeria recover from borers?
Often yes, if the borer is limited to a branch and you cut below the damage. Plumeria usually branches again from below the cut. If the main trunk is hollowed, the outlook is worse, and you should get a second opinion.
What does borer damage look like on plumeria?
Look for small round holes, sawdust like frass, sap oozing and a single branch that wilts or breaks. Cutting the branch open may show a tunnel. Rot looks wet and mushy by comparison, and freeze damage has no holes.
Is the plumeria longhorn borer found outside Hawaii?
The species is recorded in the southwestern United States, Mexico and parts of the Caribbean and Central America. How much it affects plumeria in those places is not well documented. Your local extension office can tell you what is active in your area.
Can I save a cutting from a borer infested branch?
Only use a piece that is clean, solid and tunnel free along its whole length. Do not root a section with holes or frass, since a grub could still be inside. When in doubt, discard it.
Should I spray my plumeria for borers?
Sprays rarely reach grubs inside the wood. Pruning out infested branches is the most dependable step. Sprays are better kept for pests that live on the surface.