Dr. Phyto

common rhododendron

Rhododendron ponticum

Diseases & pests on this plant

• vine weevilOtiorhynchus sulcatus

  Distinctive U-shaped notches around leaf margins (similar to Sitona on legumes), C-shaped white legless larvae (up to 10mm) feeding on roots inside pots, sudden plant collapse during summer despite normal watering (larvae have eaten all roots), adults visible at night feeding on foliage.

• Cercospora leaf spot of rhododendronCercospora rhododendri

  Small (3-10mm) round-to-angular brown spots on upper leaf surfaces, spots often have purplish-red borders + grey-tan centers, severely affected leaves yellow + drop, mostly cosmetic on healthy plants but stresses weak/young plants.

• Phytophthora root + crown rotPhytophthora cinnamomi

  Sudden wilting + collapse of mature trees during summer heat stress, dark sunken cankers at base of trunk often oozing dark sap, root system rotted away to small white feeder roots only, gradual general decline + sparse foliage 1-3 years before final collapse, characteristic V-shaped soil-line lesion when bark peeled back.

• sudden oak death / Ramorum blightPhytophthora ramorumEU-notifiable quarantine organism

  Dark brown leaf blotches often starting at leaf tip + spreading along midrib, bleeding cankers on stems + trunks (oozing dark sap), wilting + dieback of branches, complete tree death possible within 2 years (oak + larch); shrub hosts (Rhododendron) show leaf blackening + stem dieback.