Plant Disease · Plant disease
Tan Spot
Pyrenophora tritici-repentis (anamorph Drechslera tritici-repentis)
Also known as: Yellow leaf spot, Wheat tan spot, Yellow spot
Tan spot is a foliar fungal disease of wheat caused by Pyrenophora tritici-repentis. It produces tan lesions with yellow halos, is strongly favoured by cereal residue left on the surface, and can reduce grain fill when it moves onto the upper leaves.
Tan spot, caused by the fungus Pyrenophora tritici-repentis, is a common leaf disease of wheat that has become more prominent with the adoption of reduced-tillage and residue-retention systems. The fungus overwinters readily on wheat stubble left on the soil surface, so fields returned to wheat after wheat under minimum tillage are at particular risk.
The pathogen produces host-selective toxins that cause characteristic tan necrotic spots and yellowing, and different races of the fungus differ in which toxins they produce. Because symptoms can resemble other leaf spots and nutrient effects, careful examination and, where needed, laboratory confirmation are useful for a correct diagnosis.
Symptoms and identification
Tan spot typically appears as small tan-to-brown flecks that enlarge into oval or diamond-shaped lesions surrounded by a yellow halo. A tiny dark spot is often visible near the centre of the lesion where infection began. As lesions coalesce, large areas of leaf can turn tan and die, and severe cases produce extensive yellowing of the canopy.
Pathogen and disease cycle
Pyrenophora tritici-repentis survives between seasons on infected wheat residue, where it forms sexual fruiting bodies (pseudothecia). In spring these release ascospores that infect the lower leaves of a new crop. Asexual conidia produced on the lesions are then spread by wind and rain within the crop, carrying the disease up the canopy through repeating cycles under favourable weather.
- Infected wheat stubble is the main source of primary inoculum
- Ascospores from residue initiate infection on lower leaves
- Wind- and rain-dispersed conidia spread the disease up the canopy
- Host-selective toxins drive the necrosis and yellowing symptoms
Hosts and favourable conditions
Wheat is the primary host, with triticale also susceptible. The disease is strongly tied to management: continuous wheat, reduced tillage, and heavy surface residue all increase the pool of overwintering inoculum. Warm, humid weather with extended leaf wetness then favours infection and spread.
- Wheat-after-wheat cropping with surface residue retained
- Warm temperatures combined with high humidity and leaf wetness
- Reduced or no-till systems that keep infected stubble at the surface
- Susceptible varieties that allow rapid lesion development
Management principles
Because infected residue drives tan spot, management centres on breaking the residue-to-crop link through rotation and residue handling, backed by resistant varieties. These reduce how much inoculum reaches a new crop and how quickly disease develops.
- Rotate away from wheat to reduce carry-over on stubble
- Manage residue through incorporation or decomposition where suitable
- Grow varieties with better tan-spot resistance ratings
- Avoid dense canopies that trap humidity and prolong leaf wetness
- Scout the upper leaves during stem elongation and heading
Relationships
Evidence-backed connections in the knowledge graph.
Risk increases under
Scope & limitations
Geographic scope: Global; common in wheat-growing regions using reduced tillage and continuous wheat, with severity varying by residue management, rotation, and weather.
Climate context: Favoured by warm, humid weather with extended leaf wetness; surface wheat residue provides the overwintering inoculum that starts each season.
- This is a general overview and does not replace field diagnosis or region-specific extension guidance.
- Pathogen races and their toxin profiles vary by region and change over time; consult local authorities for current status.
- Control-product recommendations are jurisdiction-specific and are deliberately not provided here.
Sources
This article draws on the following authoritative sources. See our sources & methodology for how they are selected.
- [1]CABI Digital Library — Crop Protection Compendium (opens in a new tab)High
CABI (Centre for Agriculture and Bioscience International)
Cited for: Pathogen biology, disease cycle, and host range
- Type:
- Reference database
- Jurisdiction:
- Global
- Accessed:
- 2026-07-12
- [2]EPPO Global Database (opens in a new tab)Authoritative
European and Mediterranean Plant Protection Organization (EPPO)
Cited for: Pathogen nomenclature and distribution
- Type:
- Reference database
- Jurisdiction:
- Global
- Accessed:
- 2026-07-12
- [3]Iowa State University Extension and Outreach (opens in a new tab)High
Iowa State University Extension and Outreach
Cited for: Identification and residue-based management in wheat
- Type:
- University extension service
- Jurisdiction:
- United States (Iowa)
- Accessed:
- 2026-07-12