Poplar bacterial canker
Sunken, oozing cankers on young shoots, branches and the trunk of poplar, with a slimy creamy-white or brown spring ooze — a nursery-carried bacterial disease that deforms the bole and opens the way for borer and die-back.
- Pathogen
- Bacterium (Xanthomonas populi)
- Spreads by
- Infected cuttings/ETPs, rain-splash & tools; wounds
- Favoured by
- Warm, wet spring weather; wounded, stressed young trees
- Main risk
- Deformed bole, downgraded logs, entry for borer & die-back
Overview
Poplar bacterial canker is caused by Xanthomonas populi, a bacterium that infects Populus deltoides and related poplars through leaf-scars, pruning cuts and bark wounds. It builds slowly inside the bark and, in spring, breaks through as sunken, elongated cankers on young shoots, side branches and eventually the main trunk. From these cankers a slimy creamy-white or brown ooze leaks out in the first warm-wet weather of the season — the diagnostic sign that separates this disease from the fungal die-back that also attacks stressed poplar.
A repeatedly cankered tree loses its side branches, develops a knotted, deformed bole that is downgraded from peeler to packing-wood grade at the mill, and gives Apriona stem borer and wound-invading fungi (Botryodiplodia, Cytospora) ready entry points into the trunk. The disease travels most readily on infected planting material — cuttings and ETPs lifted from a diseased mother block — so on a fresh planting the largest single control decision is where the ETPs come from. Once the pathogen is inside the trunk there is no cure spray; management combines clean planting material, tolerant clones, dry-season pruning back into healthy wood, and protecting fresh cuts with a Bordeaux paste or copper wash.
How to identify it
- Sunken, elongated, cracked cankers on young shoots, side branches and, over time, the main trunk of the tree.
- A slimy creamy-white or later brown bacterial ooze leaking from the canker in the first warm-wet spring weather.
- Repeated die-back of the tip of an affected shoot or branch, and a knotted, deformed section of the trunk where old cankers have healed over crookedly.
- A pattern of new cankers on the same young block year after year — the tell-tale sign the planting material itself came in infected.
What causes it and when
- The bacterium Xanthomonas populi, which enters through leaf-scars, pruning cuts and mechanical bark wounds and multiplies inside the bark before breaking out as a canker.
- Most fresh infection on a new block travels in on infected cuttings and ETPs lifted from a diseased mother block — the single biggest source.
- On a live block the bacterium spreads short distances by rain-splash, on unclean pruning tools and, once cankers are open, by insects visiting the ooze.
- Cankering and ooze are worst in the warm, wet spring flush, and on trees stressed by water shortage, mechanical wounds or a heavy defoliator/borer year.
Cultural & organic control
- Plant only healthy, canker-free ETPs and cuttings from a WIMCO/PFRI-linked or state-forest nursery — refuse any batch with visible cankers on the stem.
- Grow tolerant/less-susceptible clones (the PFRI Uday, Bahar and Kranti releases are among the better options; ask your state forest research institute for the current list).
- Cut affected shoots and branches back to clean healthy wood in the cool dry months (December–February) and burn the trimmings — not compost them.
- Paint every fresh cut and pruning wound with Bordeaux paste or a recommended copper wash so the bacterium cannot enter through it.
- Disinfect pruning tools between trees with a bleach or spirit dip so a diseased tree does not seed the next one.
Chemical control
- There is no curative spray for tissue that is already cankered — copper is protective, not curative.
- A protective copper-based bactericide (e.g. copper oxychloride) applied to the trunk and lower canopy just before the warm-wet spring flush, and again after any major pruning, cuts fresh infection through wounds.
- Combine copper with prompt Apriona stem borer control — borer wounds are one of the main entry points the bacterium exploits.
- Confirm the current recommended copper schedule for your area with your state forest research institute (FRI Dehradun) or the nearest KVK.
Prevent it coming back
- Never take cuttings or lift ETPs from a mother block that has cankered trees — that is how a clean new field turns into a chronically cankered one.
- Prune and sanitise in the dry season, disinfect tools between trees, and protect every fresh cut with Bordeaux paste.
- Keep the block well-watered in its first two summers and control defoliator and Apriona borer promptly, so trees are neither stressed nor wound-invaded.
- Where a block is already chronically cankered on all trees, felling early and replanting with clean ETPs on a rotated site is often cheaper than nursing the diseased block to full rotation.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
My young poplar trees have sunken cracked patches on the trunk with a creamy ooze in spring. What is it?
Those sunken, elongated, cracked cankers with a slimy creamy-white or brown ooze in the first warm-wet spring weather are poplar bacterial canker (Xanthomonas populi). There is no cure spray for tissue that is already cankered — cut affected shoots and branches back to clean healthy wood in the cool dry months, burn the trimmings, paint fresh cuts with Bordeaux paste, and protect the new spring flush with a copper spray. If cankers appear on many trees in the same young block, the planting material itself likely came in infected — flag it to the nursery.
Why does the block I planted last year already have canker on many trees?
A pattern of fresh cankers on the same young block year after year almost always means the cuttings or ETPs came in infected — Xanthomonas populi is carried inside the planting material from a diseased mother block. That is why the single biggest control decision on a fresh poplar planting is where the ETPs come from: only lift or buy from a WIMCO/PFRI-linked or state-forest nursery that keeps canker-free mother blocks, and refuse any batch with visible cankers on the stem.
How is poplar bacterial canker different from ordinary die-back on a poplar tree?
The two often occur together but have different causes and different management. Bacterial canker is caused by the bacterium Xanthomonas populi and shows sunken cracked cankers with a slimy spring ooze on the bark; it travels on infected planting material and is prevented by clean ETPs, dry-season pruning and copper on fresh cuts. Die-back is caused by wound-invading fungi (Botryodiplodia, Cytospora), shows drying-back of shoots from the tip and dry sunken bark discolouration without an ooze, and is prevented by not stressing the tree — irrigation, wound protection, borer control. A block with heavy canker usually has some die-back too, because the canker wounds open the way for the fungi.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.