Rules: Dragon Weaknesses

A dragon is vulnerable to the type of energy that opposes its elemental subtype, as noted in the Monster Manual. A dragon takes half again as much (+50%) damage as normal from attacks involving its opposing energy type, regardless of whether a saving throw is allowed, or if the save is a success or failure. The feats Overcome Weakness and Suppress Weakness reduce this vulnerability.
Clerics with access to the air, earth, fire, or water domains can turn, destroy, rebuke, or command dragons of the appropriate elemental subtype. Since the effectiveness of these abilities is based on the defending creature’s Hit Dice, older and larger dragons seldom fall prey to them, but they can be effective against smaller and younger dragons.