Yellow Leaf Spot of Wheat

Note Number: AG1114
Published: June 2006
Updated: May 2009

This Agnote provides Victorian grain growers with information on the management of yellow leaf spot disease in wheat.

Yellow leaf spot in Victoria

In the past, yellow leaf spot was only seen at low levels in Victorian wheat crops. However, in recent years the wide spread cultivation of susceptible wheat varieties like Yitpi, increased stubble retention, and intense wheat production have seen the incidence of yellow leaf spot increase.

What to look for

Yellow leaf spot, also known as tan spot, is a common disease of wheat. The disease is most often observed in seedlings, but when conditions are suitable, it can progress up the plant where it causes significant yield loss.

The first symptoms appear on leaves as small yellow-brown oval spots or lesions. Lesions may expand to 1 cm in diameter, and are surrounded by a yellow margin (Figure 1 and 2). Individual lesions may vary in shape and size, often expanding and joining together with other lesions. The tips of severely affected leaves soon yellow and die (Figure 3). Symptoms of yellow leaf spot can be confused with aluminium toxicity.

Disease cycle

Yellow leaf spot, caused by the fungus Pyrenophora tritici-repentis, is predominantly a stubble-borne disease. The fungus survives from season to season on stubble in small black fruiting bodies (Figure 4). These fruiting bodies contain large numbers of spores which are forcibly ejected during humid conditions. Spores land on nearby wheat plants and will infect leaves if they remain wet for more than 6 hours.

Often the early infection of seedlings does not progress to adult plants. However, when conditions are wet during the season, a second type of spore is produced. This secondary spore is dispersed by the wind and can result in rapid disease development higher up the plant; and in other wheat crops. It is secondary spread that causes high yield loss.

Economic importance

In isolated cases, particularly in wheat crops sown into wheat stubble, heavy infestations have caused high yield losses. In the Mallee in 2001, conditions were conducive for secondary infection and losses of 10-15% occurred in the more susceptible varieties.

Management

Yellow leaf spot is most severe where successive wheat crops are grown on retained stubble. Rotating wheat with barley, oats or a non cereal crop will reduce the impact of this disease. Foliar fungicides are registered to control yellow leaf spot, but they may not be economical. Management options include:

• Not sowing wheat into infected stubbles.
• Avoiding susceptible varieties (see Cereal Disease Guide AG1160). Reducing the number of susceptible crops grown in a district will reduce inoculum load from season to season.
• Fungicides are most likely to give an economic return when yield potential is above 3.0 t/ha, a susceptible variety is being grown, and 5% of the Flag (-2) leaf and Flag (-3) leaf are affected (see Figure 5). Under these conditions, a fungicide application should be made prior to or just after rain, between flag leaf emergence and late booting. This will prevent the disease from moving up onto the flag leaf (see Cereal Foliar Fungicides AG1190).
• Seed treatments are not effective against this disease.

Further References

More detailed information can be obtained from the DPI Information Note Series

Cereal Diseases Guide (AG1160).

Cereal Foliar Fungicides (AG1190)

Wallwork H (2000) Cereal Leaf and Stem Diseases.

Wurst M, Wilhelm N, Brennan R (2001) Winter Cereal Nutrition: The Ute Guide.

Contact/Services available from DPI

DPI Field Crops Pathology, Grains Innovation Park, 110 Natimuk Rd, Horsham 3400. Tel (03) 5362 2111, or the DPI Customer Service Centre 136 186.

Acknowledgements

This agnote was developed by Grant Hollaway June 2006 and reviewed by Frank Henry, Farm Services Victoria - BioSciences Research, May 2009. Financial support by the GRDC is gratefully acknowledged.