pistachio twig blight

Plants affected

• pistachio
• mastic tree

Easily confused with

• pistachio leaf blight

  How to tell them apart: Septoria pistaciae makes small (1-5 mm) circular leaf spots scattered over the upper leaflet surface, each with a pale tan-to-grey centre ringed by a sharp purple-brown border; with a hand lens you see tiny embedded black dots (pycnidia) in the pale centre, and in humid weather these ooze thin whitish threads (cirri). Lesions stay small and numerous, and heavy infection causes premature leaf drop. Pestalotiopsis pistaciae instead produces larger, more diffuse brown-to-greyish necrotic blotches that often start at the leaf tip or margin and spread inward in irregular zones, frequently with a faint concentric (target-like) banding. Its fruiting bodies are flatter black acervuli that under humidity push out sticky black spore masses (often with fine bristle-like setae), giving the dead tissue a sooty, smudged look rather than crisp purple-rimmed dots.

• pistachio rust

  How to tell them apart: Pileolaria terebinthi (pistachio rust) shows reddish-brown to violet, somewhat angular spots with a yellowish halo, mostly on the LOWER leaf surface; as it matures these become rough, crusty, scab-like dark-brown telia and the leaf curls or corrugates and drops early. Pestalotiopsis pistaciae instead makes greyish-brown necrotic blotches, often with concentric zoning and a darker margin, dotted with tiny BLACK pinhead acervuli that ooze a dark slimy spore mass when wet, and it commonly runs back into the shoot causing tip dieback. So: orange-to-rusty angular spots and crusty stalked telia on the leaf underside point to the rust, whereas grey zoned blotches with black specks plus shoot dieback point to Pestalotiopsis.

• pistachio Septoria leaf 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 Verticillium wilt

  How to tell them apart: Pestalotiopsis pistaciae (fungal leaf/twig blight): Look at the leaves and small twigs. Necrosis begins at the leaf margin or tip as grey-brown to ash-grey dead patches, often with a darker brown border separating dead from green tissue. On older lesions, tiny black fruiting bodies (acervuli) appear as raised dots, sometimes oozing black, tendril-like spore masses when humid. Twig dieback works from the tip inward, and affected shoots often show small bark cankers. Symptoms are scattered and worse in warm, wet, humid conditions. Verticillium dahliae (vascular wilt): The give-away is internal — peel back the bark on a wilting branch and you see brown to dark streaking in the wood (vascular discolouration); the leaf surface itself has no black fruiting dots. Whole shoots or one side of the tree wilt and the leaves scorch from the margins inward but stay attached, often in a sudden one-sided (sectorial) pattern reflecting blocked water vessels. There are no acervuli or spore tendrils on the surface. Symptoms intensify with water stress and are tied to infested soil rather than humid air.

Common questions

Do I have to report pistachio twig blight?

No. pistachio twig 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 twig 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.