Bees and Wasps Swarming Elm Tree: Slime Flux Diagnosis

Our tall elm has bees/wasps swarming high up. Leaves are falling, suggesting a pest infestation attracting the insects. We're considering removal but want to understand the problem first.

Diagnosis: Slime Flux (Wetwood)

The swarming insects indicate either slime flux or alcoholic flux—both bacterial infections causing sap fermentation.

Slime Flux (Acidic Flux)

Bacteria ferment sap inside the trunk; it seeps out through wounds or bark cracks. The acidic, vinegar-smelling liquid attracts sweet-feeding insects (wasps, bees, yellow jackets). Infection can be surface-level or deep within the trunk.

Alcoholic Flux (Frothy Flux)

Microorganisms ferment sap in bark cracks and cambial wounds. The nearly colorless, acidic froth emits a pleasant fermentative odor and appears temporarily in summer. Common on stressed elms, oaks, sweetgums, and willows. Heat stress is a primary trigger.

Management

No cure exists. Wash the trunk to discourage insects: mix 1 pint chlorine bleach per gallon of water for a final rinse. Sap flow is periodic—it may disappear permanently or recur annually. Prevent future issues with proper watering (avoid overwatering), protect from mower/trimmer damage, and maintain overall tree vigor.