sudden oak death / Ramorum blight

Symptoms

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.

Easily confused with

• vine weevil

  How to tell them apart: On rhododendron, Phytophthora ramorum is a fungus-like pathogen: look for dark brown to blackish necrotic blotches spreading from the leaf tip or along the midrib, blackened petioles and shoots, and wilting tip dieback that progresses downward, often after wet, mild weather. Otiorhynchus sulcatus (black vine weevil) is an insect: adults chew unmistakable angular U-shaped notches into the leaf margins (never on the leaf interior), while the legless, C-shaped white grubs with brown heads eat the roots and girdle the stem base, causing whole-plant wilt with intact, un-notched green leaves. Decisive sign: marginal leaf notching plus white root grubs means weevil; spreading dark leaf and shoot lesions with no marginal notches means Phytophthora. If you suspect ramorum, do not move the plant.

• Phytophthora root + crown rot

  How to tell them apart: On Camellia japonica, Phytophthora cinnamomi is a soil-borne root rot: it rots the fine feeder roots (turning them blackish-brown and brittle), produces a reddish-brown V-shaped canker at the soil line/crown, and the canopy slowly yellows, wilts and dies back over 1-3 years while symptoms rise FROM the base upward; the roots are visibly decayed. Phytophthora ramorum is an aerial blight with healthy roots: look for dark brown, water-soaked leaf lesions with a sharp defined margin starting at the leaf tip or petiole and running down the midrib, blackened spreading stem cankers and shoot dieback on the UPPER plant, plus rapid leaf drop a few days after infection. Rule of thumb: damage rising from the soil line with rotten roots = P. cinnamomi; lesions and dieback on leaves and shoots with sound roots = suspected P. ramorum. P. ramorum is an EU-quarantine notifiable organism (Reg. 2019/2072 Annex II), so if the upper-plant pattern fits, do NOT prune or move the plant and report it to your national plant-health authority (NPPO) first.

• camellia flower blight

  How to tell them apart: Check WHICH organ is browning. Ciborinia camelliae (camellia flower blight) attacks only the flower: tan-brown rings spread from the petal base, the whole bloom turns brown and collapses within about 48 hours, dropped petals carry hard black sclerotia (seed-like discs) on the ground, and the leaves stay green and healthy. Phytophthora ramorum (Ramorum blight / sudden oak death) instead attacks the foliage and wood: dark brown blotches start at the leaf tip and run down the midrib, shoots die back, and stems show bleeding dark cankers — never any sclerotia. If the browning is on leaves, shoots or stems (not confined to the petals), treat it as suspected P. ramorum, which is an EU-regulated notifiable quarantine organism: do not prune or move the plant and report it to your national plant protection organisation (NPPO).