pistachio Septoria leaf blight

Symptoms

Small angular brown spots on leaves with yellow halos, premature defoliation, weakened trees with reduced kernel fill, accelerated alternate-bearing cycle.

Plants affected

• pistachio

Easily confused with

• pistachio leaf blight

  How to tell them apart: Mycosphaerella pistacina is the teleomorph (sexual stage): look for tiny black, slightly raised pseudothecia (pinhead fruiting bodies) embedded in older, greyed-out necrotic patches on the upper leaf surface, often on fallen or over-wintered leaves. Spots tend to be larger, more diffuse, with a faded tan-grey centre and an irregular margin. The damage is most evident late in the season and on senescing foliage. Microscopically the fruiting bodies release two-celled ascospores rather than thread-like conidia.

• pistachio twig blight

  How to tell them apart: On pistachio leaflets look for many small (1-4 mm), roughly circular to angular brown spots, each ringed by a yellow (chlorotic) halo; spots stay flat and dry and often coalesce into larger reddish-brown blotches that trigger heavy late-summer defoliation. Hold a leaf to the light: the necrotic centres carry only pinpoint dark fruiting bodies (pseudothecia/pycnidia), never a glistening black slimy spore mass. Damage is confined to leaf blades and the disease spreads in wet, humid orchard conditions. Pestalotiopsis lesions start as brown leaf spots too, but they enlarge into greyish-tan necrotic patches with a darker brown margin and frequently sit at the leaf tip or edge rather than scattered across the blade. The diagnostic sign is on the dead tissue: tiny raised JET-BLACK fruiting bodies (acervuli) that under moisture ooze a shiny black spore mass; crucially the fungus then advances into twigs and shoots, causing cankers and tip dieback that Mycosphaerella never produces. Suspect it especially on stressed or wounded trees.

• pistachio rust

  How to tell them apart: Septoria leaf spot caused by Mycosphaerella pistacina shows small, sharply defined, angular brown-to-black spots on the upper leaf surface, typically 1-3 mm and often bounded by leaf veins. Tiny black dots (pycnidia) sit within the older spots and can be seen with a hand lens. Spots stay flat and do not raise into pustules; heavy infection causes general yellowing and premature leaf drop in humid late-summer conditions. Pistachio rust caused by Pileolaria terebinthi begins as faint chlorotic or pale necrotic flecks, but soon erupts into raised orange to yellow-brown pustules (uredinia) mainly on the lower leaf surface that release rust-coloured powdery spores onto a finger. Later in the season these darken to chestnut-brown to black telia. The powdery, erupting, raised texture and spore rub-off are the decisive signs absent in flat Septoria spots.

Common questions

How do I recognise pistachio Septoria leaf blight on pistachio?

Small angular brown spots on leaves with yellow halos, premature defoliation, weakened trees with reduced kernel fill, accelerated alternate-bearing cycle.

Do I have to report pistachio Septoria leaf blight?

No. pistachio Septoria leaf blight is not a notifiable organism, so there is nothing to report to an authority. Treat it as a normal garden problem.

How is pistachio Septoria leaf blight 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.