Grains Research and Development

Date: 01.09.2002

Barley disease warning: net form of net blotch

CORRECT IDENTIFICATION, careful crop management and strategic use of fungicides will be needed if barley growers are to avoid widespread damage from the net form of net blotch.

In a preemptive warning for southern region crop advisers, SARDI Cereal Pathologist Hugh Wallwork has indicated the net form of nct blotch will become more prominent as a leaf disease, as varieties previously rated resistant become more susceptible.

The fungus has already mutated twice in recent years in SA. Firstly on Skiff in 1996 and then in 2000 the disease was observed affecting the popular varieties Schooner and SloopPBR logo, varieties that previously showed little or no infection. Only low levels of infection were observed in 2001 due to unfavourable conditions for this disease.

Cereal pathologists in SA, Victoria and southern NSW believe it is only a matter of time before the breakdown becomes evident in the other southern states.

Until now, control of the net form of net blotch has mainly been through the use of resistant varieties.

Identification

Researchers highlight the importance of correct identification , as the net form of net blotch is a far more severe leaf disease than the spot form of net blotch.

The net form of net blotch (Pyrenophora teres f. teres) is a fungus, which is closely related to the spot form, and its biology is quite similar. The net form is carried via infected seed as well as stubble.

The net form of net blotch develops as fine, dark-brown lines along and across the leaf blades, creating a distinctive net-like pattern. Older lesions appear as larger, dark, elongated lesions with a yellow margin.

Infection requires moist, warm conditions (15- 25°) and so is favoured by early sowing. Humid conditions while the crop is maturing may allow the fungus to infect seed, leading to greater infection in crops the following year.

For accurate identilication, send samples to your nearest cereal pathologist (see contacts over page). Publications such as the Cereal Diseases Ute Guide and a new edition of the Cereal Leaf and Stem Diseases book are available from GRDC's publications outlet, Rural Connect, on 1800110044.

Free copies of the GRDC Back Pocket Guide to Wheat and Barley: Leaf Symptoms can be obtained via the order form on the GRDC web site www.grdc.com.au/bookshop/frcc.htm or by ringing GRDC on 02 6272 5525.