Troubleshooting
Willow Oak problems — and how to fix them
Willow Oak (Quercus phellos) is generally forgiving once you match its basics, but a few issues come up again and again. Here is what each one looks like, why it happens, and the fix.
Chlorosis on alkaline soils
Willow Oak is strongly calcifuge; planting in soils above pH 7.0 causes iron and manganese deficiency, resulting in yellowing leaves with green veins (interveinal chlorosis). Correct with soil acidification or chelated iron/manganese supplements. Test soil pH before planting.
Oak Wilt (Bretziella fagacearum)
As a member of the red oak group, Willow Oak is susceptible to this fatal vascular disease. Wilting starts at branch tips and progresses rapidly. Avoid wounding trees April–July; sterilise pruning tools. Contact a certified arborist if oak wilt is suspected.
Acorn Weevils (Curculio spp.)
Larvae of acorn weevils tunnel into the abundant small acorns, destroying seeds. Not harmful to tree health but reduces viable seed. The heavy annual acorn drop on paved areas can be a litter nuisance in urban plantings.
Prevent willow oak problems before they start
Most willow oak issues are care-mismatch, not bad luck. Dial in the basics:
Willow Oak problems — FAQ
Why is my willow oak chlorosis on alkaline soils?
Willow Oak is strongly calcifuge; planting in soils above pH 7.0 causes iron and manganese deficiency, resulting in yellowing leaves with green veins (interveinal chlorosis). Correct with soil acidification or chelated iron/manganese supplements. Test soil pH before planting.
Why is my willow oak oak wilt (bretziella fagacearum)?
As a member of the red oak group, Willow Oak is susceptible to this fatal vascular disease. Wilting starts at branch tips and progresses rapidly. Avoid wounding trees April–July; sterilise pruning tools. Contact a certified arborist if oak wilt is suspected.
Why is my willow oak acorn weevils (curculio spp.)?
Larvae of acorn weevils tunnel into the abundant small acorns, destroying seeds. Not harmful to tree health but reduces viable seed. The heavy annual acorn drop on paved areas can be a litter nuisance in urban plantings.