What to Do When Your South Carolina Fruit Trees Show Cankers

Cankers are among the most serious and visually obvious problems that can affect fruit trees in South Carolina. They often start small but can girdle branches or entire trunks, causing dieback, reduced yields, and eventual death of the tree. This article explains what cankers are, how to identify the most common causes in South Carolina, practical steps for immediate response, longer term control options, and prevention measures that will keep your trees healthier year after year.

What is a canker?

A canker is a localized area of dead bark and cambium tissue on a woody plant. Cankers can be caused by fungi, bacteria, environmental injury, or by a combination of stress and pathogens. They appear as sunken, discolored, cracked, or gummy lesions on branches or trunks. When a canker girdles the branch or trunk, it cuts off nutrient and water flow and leads to dieback beyond the lesion.

Why South Carolina growers should pay attention

South Carolina has a warm humid climate, with wet winters and springs in many areas, and hot summers. Those conditions favor many fungal and bacterial canker pathogens. Additionally, common local practices and stresses — late frosts, sunscald on thin-barked trees, mechanical injury, poor drainage, and excessive late-season fertilization — increase susceptibility. Home orchards and small commercial plantings need active monitoring because cankers spread from branch to branch and between trees if not addressed.

Common canker pathogens in South Carolina

Fungi often involved

Cytospora (Leucostoma) — especially important on peaches, nectarines, and other stone fruits. Appears as sunken cankers with orange or dark gum exuding on cold-damaged or stressed wood.
Botryosphaeria — attacks many fruit trees and is favored by drought or other stress. Produces dark, sunken lesions often with marginal fungal fruiting bodies when examined closely.
Phomopsis — causes twig blight and canker on pears and stone fruits, often after wet springs.
Nectria and Nectriopsis species — cause necrotic bark lesions on apples and other trees, sometimes following winter injury.

Bacteria and other agents

Fire blight (Erwinia amylovora) — a bacterial disease that causes rapid wilting and shepherds-crook symptoms on blossoms, shoots, and cankers on apples and pears. Active in warm, wet conditions during bloom and early shoot growth.
Pseudomonas syringae and other opportunistic bacterial pathogens — can invade through wounds and create canker-like lesions.

Environmental causes

Sunscald and frost injury create dead bark that becomes a site for secondary infection.
Mechanical injuries from lawn equipment, pruning, or animals provide entry points.
Root rot pathogens or saturated soils weaken the tree and make it more vulnerable to canker fungi.

Recognizing canker symptoms

Sunken, discolored lesions on trunk or branches that may be slightly swollen at the margins.
Cracked bark that flakes away to reveal dark or brownish dead wood.
Gumming or ooze, particularly on stone fruits (gummosis).
Dieback of shoots and branches beyond the lesion; foliage beyond the canker may wilt or scorch.
Fruiting bodies or discoloration in cross section of the wood when bark is removed.
In the case of bacterial fire blight: blackened, wilted shoots with a characteristic “shepherds-crook” at the tip and sticky ooze.

If you are unsure whether a lesion is a canker, scrape the bark back with a knife. If the cambium beneath is brown or black and does not produce green tissue when alive, it is likely a canker.

Immediate steps when you find a canker

Isolate the tree mentally as a potential source of infection; avoid moving pruning debris through the rest of the orchard.
Prune out infected branches promptly, during dry weather if possible, and disinfect pruning tools between cuts.
Remove and destroy severely infected branches and small trees if the trunk is girdled or the branch structure is irreparably damaged.
Improve tree vigor to reduce spread: water during dry spells, correct nutrient imbalances based on a soil test, and reduce compaction or poor drainage.
Record the location and timing of infections to help with future management and to inform professional assessment if needed.

How to prune infected wood — step by step

Make cuts at least 6 to 12 inches (15 to 30 cm) below the visible margin of the canker. Fungal pathogens often extend beyond the visible discoloration; making a conservative cut reduces the chance of leaving infected tissue.
Use sharp, well-maintained tools. For small branches use bypass pruners; for larger limbs use loppers or pruning saws.
Disinfect tools between each cut: wipe blades with 70% isopropyl alcohol, a 10% household bleach solution (followed by rinsing to prevent corrosion), or a commercial disinfectant. For high-risk pathogens like fire blight, disinfect after every single cut.
Make clean cuts without leaving stubs. For main scaffold limbs or trunk wounds larger than 2 inches (5 cm), avoid flush-cutting into the trunk; instead, make a proper pruning cut that preserves the branch collar so the tree can compartmentalize the wound.
Remove and destroy pruned material. Do not leave infected branches on site or chip them for use as mulch. Burn or dispose of material off-site according to local regulations, or cover and remove.
Avoid using wound paints or sealers routinely; research shows limited benefit and possible interference with natural healing. Paints may be considered only for large trunk wounds in very specific situations and only with expert advice.

Chemical and biological controls

Dormant copper sprays: Applying a copper fungicide in late winter or early spring can reduce overwintering bacterial and fungal inoculum on bark and buds. Follow label directions and do not exceed label rates; copper can injure some stone fruits if applied improperly.
Protective summer sprays: For fungal canker pathogens, scheduled fungicide applications during critical infection periods (wet weather, spring) using products labeled for your tree and pathogen can reduce new infections. Active ingredients used for twig and blossom disease control include broad-spectrum contact materials; choose products labeled for canker pathogens on your specific fruit tree.
Fire blight specific control: For susceptible apple and pear cultivars during bloom, there are limited bactericidal options. In commercial pomology, streptomycin and certain copper compounds are used, but availability, timing, and legal restrictions vary. Consult Clemson Extension or a licensed crop advisor for current, legal recommendations.
Biological controls: Some antagonistic fungi and bacteria are marketed for trunk and wound protection. Their effectiveness varies and they are best used as part of an integrated program.

Always read and follow the product label. Because product availability, registration, and recommended timings change, check current local recommendations before applying chemicals.

Cultural practices to reduce canker risk

Choose resistant varieties where available. For example, select peach varieties with known vigor and field resistance to Cytospora when possible, and select fire-blight-tolerant apple and pear cultivars for low-input plantings.
Plant in well-drained soil and avoid waterlogged sites where root or collar rots weaken trees.
Mulch correctly: keep mulch 2 to 4 inches deep but pull it away from the trunk 2 to 4 inches to prevent collar moisture and rodent damage.
Maintain balanced fertility. Avoid heavy late-season nitrogen that stimulates tender growth vulnerable to pathogens and frost.
Protect trunks from sunscald and mechanical injury: paint young thin-barked trees with diluted white latex paint in winter to reduce midday bark heating and subsequent cold damage; use trunk guards to prevent mower and rodent damage.
Train young trees for open canopy to improve air flow and reduce prolonged wetness in shoots and crotches where pathogens invade.
Time pruning to minimize infection risk: avoid major pruning during wet, high-inoculum periods and avoid heavy pruning right before a prolonged wet period.

When to remove and replace a tree

Remove a tree if the main trunk is girdled or multiple scaffold limbs are infected and cannot be removed without leaving an unstable tree.
If a mature tree has recurring canker infections every year despite correct care and treatment, replacement with a resistant cultivar or different species may be the most economical option.
For young orchards, remove and replace infected trees promptly to reduce inoculum pressure for neighbors.

When removing trees, consider replanting with a different variety and improving site conditions, such as drainage and soil fertility, before replanting.

Getting professional help and local resources

Clemson Cooperative Extension is an excellent local resource for South Carolina growers. County extension agents can help identify pathogens based on symptoms and assist with management recommendations that are regionally appropriate.
For large cankers on mature trees, or if a tree poses a hazard to people or structures, hire a licensed arborist or certified tree care professional. Properly trained arborists can evaluate structural integrity, perform safe removals, and recommend treatment or replacement options.
Plant diagnostic labs can culture and identify pathogens when symptoms are ambiguous. Accurate identification improves the chance of effective management.

Practical takeaways — a checklist for action

Inspect trees regularly, especially after storms, frost events, or drought.
Prune out cankers promptly and disinfect tools between cuts.
Improve tree vigor: water, fertilize appropriately, correct drainage problems, and avoid late-season heavy nitrogen.
Use dormant copper sprays and labeled fungicides as part of an integrated program, following label directions.
Protect trunks from sunscald and mechanical injury; keep mulch away from trunks.
Consider cultivar selection and site modifications to reduce long-term risk.
Contact Clemson Extension or a certified arborist for persistent or unclear problems.

Cankers are symptoms of a tree under stress and of pathogens taking advantage of wounds or weakened tissue. The best results come from combining prompt sanitation and pruning with cultural improvements that reduce stress, plus targeted chemical controls when appropriate. With timely action and ongoing vigilance, most South Carolina fruit trees can recover from early canker infections or be protected from repeat outbreaks in future seasons.