thuja tip blight (Kabatina)

Symptoms

Scattered shoot tips turn yellow then brown and die back from the tip, usually in late winter and spring; a small black fruiting body (pycnidium) can often be seen at the base of the killed section where it meets healthy green; dieback is patchy across the plant rather than whole-branch. Distinguished from Phytophthora root rot (which browns whole plants from the base).

Plants affected

• arborvitae (thuja)
• common juniper

Easily confused with

• cypress aphid

  How to tell them apart: Kabatina thujae (a fungal tip blight) and Cinara cupressi (the cypress aphid) both turn Thuja foliage brown, but the signs differ. With Kabatina, individual young shoot tips die back from the tip toward the base, showing a sharp bronze-to-brown boundary against still-green older wood, and on the dead bark you can find tiny black, often slightly raised fruiting bodies (acervuli); damage is usually scattered tip-by-tip. With Cinara cupressi the browning spreads as larger yellowing-then-scorched patches lower in the canopy, you can see the large grey-brown soft-bodied aphids clustered on twigs and inner branches, plus sticky honeydew and black sooty mould, and live ants tending the colonies — none of which occur with Kabatina.

• cypress canker

  How to tell them apart: Kabatina thujae kills only the tips of the previous year's shoots: in spring you see scattered brown-to-ash-grey dead tips a few centimetres long, sharply cut off from healthy green foliage, often with a thin grey band and tiny black fruiting bodies (acervuli) right at the boundary where the dead tip meets the living shoot — there is no resin and no sunken bark. Seiridium cardinale instead causes whole twigs and branches to flag rust-red and die back from larger girdling cankers on the woody stems: look for an elongated, slightly sunken canker with cracked bark oozing sticky clear-to-amber resin, with dark pustules on the canker face, killing everything beyond it. In short: small dead shoot-tips with a black-dotted margin and no resin point to Kabatina, while resin-bleeding sunken stem cankers with whole rust-red flagging branches point to Seiridium.

• European pear-juniper rust

  How to tell them apart: Both Kabatina thujae and Gymnosporangium tremelloides show brown, dead twig tips scattered through otherwise green juniper foliage in spring, but the branch reveals the difference. Gymnosporangium tremelloides always produces a persistent spindle-shaped swelling (gall) on the twig or branch, and the dieback is on the shoot beyond that swelling; in damp spring weather this swelling pushes out distinctive bright orange, gelatinous, finger-like horns (telia) that no Kabatina infection ever forms. Kabatina thujae has no swelling at all: it kills only the tip of last year's shoot, leaving a small brown or grey-brown canker/lesion at the junction where the dead tip meets living green tissue, often with tiny black fruiting dots in the dead bark. So look for a year-round woody swelling with orange jelly (rust) versus a flat lesion at the base of a dead tip with no swelling (Kabatina).

• lavender root rot

  How to tell them apart: Both Kabatina thujae and Phytophthora nicotianae make Juniperus communis foliage turn brown, thin out and die back, but they attack from opposite ends. Kabatina thujae is a tip blight: scattered individual shoot tips (mostly the 1-year-old growth) turn dull green then ash-brown from the tip inward, and at the base of each dead segment you find a small sunken brown lesion or canker bearing tiny black pinhead fruiting bodies, while the rest of the bush and its roots stay healthy. Phytophthora nicotianae is a root and collar rot driven from below: whole branches or the entire plant bronze, fade and wilt fairly uniformly with no discrete tip cankers, the lower stem near the soil line shows dark watersoaked bark and the roots are blackened and rotten, and it is strongly linked to waterlogged or overwatered, poorly drained soil. Dig and check the roots and collar: firm white roots with isolated cankered tips point to Kabatina, soft black rotten roots and a dark collar point to Phytophthora.

Common questions

How do I recognise thuja tip blight (Kabatina) on arborvitae (thuja)?

Scattered shoot tips turn yellow then brown and die back from the tip, usually in late winter and spring; a small black fruiting body (pycnidium) can often be seen at the base of the killed section where it meets healthy green; dieback is patchy across the plant rather than whole-branch. Distinguished from Phytophthora root rot (which browns whole plants from the base).

Do I have to report thuja tip blight (Kabatina)?

No. thuja tip blight (Kabatina) is not a notifiable organism, so there is nothing to report to an authority. Treat it as a normal garden problem.

How is thuja tip blight (Kabatina) treated?

Mainly with biological and cultural measures — removing affected material, changing the conditions that favour it, and treating with agents approved in your country. The exact steps and their timing depend on the plant, the season and where you live: Dr. Phyto works them out in a free diagnosis.