Collar rot (Phytophthora)

A dark ooze at the base of the trunk and general decline: a soil fungus attacks the collar, often in heavy soil that stays waterlogged.

How to recognise

• Clear the soil at the base and inspect the collar: brown, soft or oozing bark below the surface is the classic sign.
• Check whether the soil often stays waterlogged there (a hollow, overwatering, clay soil).

What to do

• Expose the collar to let it dry in the air and remove soil piled against the trunk.
• Improve drainage: avoid standing water, water less often, mound up if needed.

Prevent

• Plant the graft union well above soil level and avoid watering right against the trunk.
• In heavy soil, improve drainage at planting (sand, compost, raising the bed).

Trees affected