Eyespot of winter cereals – an emerging disease

Eyespot is a fungal disease of cereals which occurs in medium and high rainfall zones and has been known to occur in paddocks in New South Wales and South Australia for many years. More recently, with changes in farming systems, eyespot has been causing increasing problems in South Australia. In 2016, wet seasonal conditions meant severe eyespot expression occurred leading to a build-up of inoculum levels in affected paddocks. This has meant significant incidence of eyespot in 2017, despite drier conditions early in the season, and will contribute to inoculum levels in 2018.

Eyespot lesions are found on stem bases and have a distinct eye-shape, with a darker border and a pale centre with black spotting caused by fungal growth (Figure 1). One or more lesions can be present on a stem. True eyespot (caused by Oculimacula yallundae) can be misidentified as sharp eyespot (caused by Rhizoctonia solani).

Figure 1 Distinct eye-shaped lesions with dark borders and paler centres with black spots caused by eyespot. Right hand stem shows stem buckling due to stem weakening

Figure 1 Distinct eye-shaped lesions with dark borders and paler centres with black spots caused by eyespot. Right hand stem shows stem buckling due to stem weakening. Source: Marg Evans, SARDI

Research trials conducted by SARDI and funded by the GRDC indicate that susceptible bread wheat varieties may have yield losses in the range of 19%-35% (0.6-1.3 t/ha). Eyespot lesions alone are a major contributor to those yield losses.  Lesions also weaken stem walls, resulting in the weakened stems buckling and lodging. As the stems fall in all directions, crops which lodge due to eyespot (Figure 2) are difficult to harvest, leading to further yield losses and an increased risk of weather damage to grain.

Figure 2 Lodged crop as a result of eyespot infection in Saintly durum wheat crop at Tarlee, SA.

Figure 2 Lodged crop as a result of eyespot infection in Saintly durum wheat crop at Tarlee, SA. Source: Marg Evans, SARDI

Eyespot is hosted by all cereal types and inoculum is stubble borne. Spores develop after infected stubble becomes wet at the start of the season. Once the new crop emerges, spores splash up from the infected residues onto the base of the plants during rainfall events. At least 3 days of wet (about 3 mm or more) weather is then needed for infection to occur.

Lesions develop very slowly and will usually not be readily visible until mid to late grain fill, when it is too late to manage the disease. The presence of eyespot in paddocks is often noticed only when lodging occurs and as lodging may happen in small areas or not at all, eyespot can be causing yield losses in paddocks well before its presence is identified.

Distribution and occurrence

In Australia, issues with eyespot are generally restricted to the medium and high rainfall zones of South Australia. Occasional reports of a crop being affected by eyespot in the high rainfall areas of Victoria have occurred in the last few years. In the past, eyespot affected crops on the Southern Slopes of New South Wales, but there have not been any recent reports of issues. Farming systems with intensive cereal rotations, stubble retention and reduced or no tillage are most at-risk from this disease. Early sown cereal crops are most likely to be affected.

Management of eyespot

To manage eyespot effectively, growers must know whether the disease is present. This can be done by crop inspection, including checking lodged cereal crops closely for eyespot lesions (Figure 3) on stem bases. As eyespot can be difficult to detect visually, submitting soil samples to the PREDICTA(R) B analytical service for testing is a powerful tool for determining which paddocks are at risk from eyespot.

Figure 3 Growers need to check lodged crops closely for eyespot lesions on stem bases.

Figure 3 Growers need to check lodged crops closely for eyespot lesions on stem bases. Source: Marg Evans, SARDI

Fungicides are a major tool for managing eyespot, but currently no fungicides are registered for this purpose in Australia. To manage eyespot effectively it is recommended that fungicide be applied prior to canopy closure – at stem elongation (GS30) . Registration of two fungicides and one plant growth regulant are currently being sought.

Variety resistance is another tool for managing eyespot and research trials conducted by SARDI and funded by the GRDC have demonstrated a range of resistance levels in Australian cereal varieties (Table 1).

A break from cereals will reduce eyespot inoculum, but if levels are high then it will take more than one break year to reduce eyespot risk to a low level. Burning infected residues will greatly reduce but not entirely remove inoculum and is not a desirable management tool in modern farming systems.

Table 1. Eyespot provisional resistance ratings for current SA cereal varieties

Main season wheat   Long season wheat   Barley
Trojan MS Beaufort MR-MS Fathom MRMS
AGT Katana MS-S Einstein MRMS Oxford MR-MS
DS Darwin MS-S Forrest MS Hindmarsh^ MRMS-S
DS Pascal MS-S Gazelle MS La Trobe^ MRMS-S
Emu Rock MS-S Manning MS Rosalind* MS
Yitpi MS-S Wakelin MS Compass MS
Axe S Bolac MS-S Scope MS
Beckom* S Orion S Spartacus* MS
Cobra S Wedgetail S
Corack S
Cosmick S Durum wheat   Triticale
Cutlass* S Hyperno MS Fusion MS
Gladius S Saintly MS
Grenade CL+ S Aurora S
Harper* S
Hatchett CL+* S Notes
Mace S ^Hindmarsh and La Trobe are sister lines – at some sites they were rated MRMS and at others they were rated S
Scepter* S
Scout S
Shield S
Tenfour* S *Ratings based on one season of data only
Wallup S
Wyalkatchem S

S = Susceptible, MS = Moderately Susceptible, MR = Moderately Resistant

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