A tree generally seals itself effectively, and an untreated wound seals better than a painted one. Research shows that pruning paint can seal in moisture and promote decay. In most cases, you're better off avoiding the use of tree paint or wound dressings, but there are exceptions. Trees that are troubled by diseases or pests may benefit from wound dressing to keep out the pest. For example, an oak pruned during the dormant season seals itself effectively with no extra care. However, an oak that needs to be pruned in spring or summer (from storm damage, for instance) should be sealed with wound dressing to prevent sap beetles, which carry oak wilt fungus, from being attracted to the open wound.