Black Spots on Sugar Maple Trunk: Borers or Bleeding Canker?

Your sugar maple has black, tar-like spots and stripes on the trunk and a main limb, resembling burn marks. You're worried it's a fungus or injury from swings and climbing.

Two Likely Causes

1. Borers (insects): Flatheaded or roundheaded borers tunnel under bark, causing sap to ooze and darken. Look for small holes, sawdust-like frass, or loose bark.

2. Bleeding Canker (disease): A bacterial or fungal infection that causes dark, wet-looking streaks. Less understood, harder to treat.

Recommended Action Plan

• Fertilize with 10-10-10 at 1 lb per inch of trunk diameter, scattered around the drip line and watered in. Do this before rain to avoid extra watering. Healthy trees resist both problems better.
• Spray trunk with Merit (imidacloprid) to kill borers if present. Apply per label—this is a systemic insecticide absorbed by the tree.
• Avoid "weed and feed" lawn fertilizers—they contain herbicides that harm trees.

Boosting overall tree health is the best strategy for either issue. Monitor for worsening dieback or increased borer evidence.