• Predicting limb breakage means learning to see and interpret the external signs that a limb is likely to fail in the near future.
• Some failures can not be predicted, and some predictions will not be right. But a sound policy can be based on "best guesses" from years of careful field observations.
• As used here, a "limb" is bigger than 3-4" in diameter (=branch), at least somewhat horizontal, and attached to a larger leader or trunk.

• Symptom: limb without bark, missing or dead leaves in crown

Problem: limb death

• Symptom: small or misshapen leaves, or early color in one spot of the crown

Problem: limb decline

• Symptom: wounds with holes or cavities, esp. on the upper side or one above the other

Problem: internal decay column, hollow limb

• Symptom: "dogleg" (sharp turn) in a limb at the point where there is an old wound

Problem: decayed stress point

• Symptom: tuft of leaves at end ("lion's tail"), or great limb length (e.g., in silver maple)

Problem: unusually high mechanical load

• Symptom: long cracks ("frost cracks") along the length of a limb, esp. if on both sides

Problem: delamination of internal layers, separation of the beams

• Symptom: diameter over 15" in a hazard species, esp. if limb is larger than central leader

Problem: limb weight beyond the normal strength of a species

• Symptom: woody plants in a union (crotch), swelling around or seepage from the union

Problem: included bark, internal decay, weak attachment of limbs

• Evaluate the target. What will the limb hit if it falls, and how serious would that be? If the limb threatens people or property, you should probably remove it.
• Identify the species. A symptomatic limb on a weak-wooded species (such as silver maple or cottonwood) is more dangerous than on a strong-wooded species (such as oak).
• Get an aerial inspection, if possible. It is difficult to tell the extent of a defect from the ground, even with binoculars.
• Make sure a correct cut is done, usually taking it back to the collar on the leader. Limbs are pretty big, so the wound will close slowly, and you want to minimize infection.
• Don't remove more than 1/3 of the crown. Besides, if that many limbs are suspect, you should probably consider removal as a more cost-effective alternative.

• How to Detect, Assess and Correct Hazard Trees, Minnesota DNR, 1993 (if unavailable, call us at 716-461-1000), or contact a professional who is skilled in hazard evaluation.