Rhododendron

Rhododendron horizon

Ericaceae · broadleaf deciduous shrub · introduced

Last updated March 8, 2026

Data Coverage 2 of 6 dimensions

Site Data

Threats

Cultivars

Phenology

GDD Thresholds

Puget Sound

Diseases (28)

Phytophthora spp. Root Rot (Phytophthora spp.) Podosphaera aphanis var. aphanis Powdery Mildew Ovulinia azaleae Ovulinia Petal Blight Non-pathogenic (iron deficiency) Lime-induced Chlorosis Symptom category — not a single disease Leaf Spot Exobasidium vaccinii Leaf and Flower Gall Cylindrocladium scoparium Cylindrocladium Blight and Root Rot Botrytis cinerea Botrytis Petal Blight Xylella fastidiosa or abiotic Marginal leaf necrosis Rhododendron and Cutting Rots Non-pathogenic (abiotic stress) Leaf Burn abiotic (drought, heat stress) or bacterial (Xylella fast... Leaf Scorch Phytophthora spp. Phytophthora Root Rot and Wilt Phytophthora ramorum Ramorum Leaf Blight Botryosphaeria dothidea Botryosphaeria Dieback Seifertia azaleae Bud Blight Rhododendron necrotic ringspot virus Necrotic Ringspot Many different Phytophthora Blight and Dieback Phytophthora ramorum"filthy five\" genera are inc Ramorum Leaf Blight and Shoot Dieback Thekopsora minima and Naohidemyces vaccinii Rust Taphrina wiesneri Witches' Broom Armillaria ostoyae Armillaria Root Rot Botrytis cinerea Botrytis Shoot Blight Pestalotiopsis sydowiana Gray Blight Non-pathogenic (physiological disorder) Physiological leaf spot Phytophthora spp. Phytophthora Blight Phytophthora spp. (P Phytophthora Root Rot Phytophthora ramorum Ramorum leaf and shoot blight (Sudden oak death)

Cultivars (1)

'Monarch'

Common name: Horizon Monarch Rhododendron; Mature height: 6 ft