Department of Agriculture, Western Australia plant pathologist Ciara Beard has warned that leaf spotting diseases yellow spot and septoria nodorum blotch have been an early problem for many growers in the Northern and Central Agricultural regions this year with the earlier rains providing ideal conditions for the diseases.

No seed dressing or in-furrow fungicides are currently registered for these diseases. Some seed treatments are registered for control of septoria tritici blotch but they are generally not used in this context.

“DAWA has trials this year at Badgingarra, Mingenew, Dalwallinu and Merredin, that will look at some of these treatments alongside foliar sprays to investigate if they have any benefit for yellow spot and septoria nodorum disease control,” said Ms Beard.

Yellow spot and septoria diseases have similar looking symptoms and frequently occur together.

They both have tan coloured blotches with mostly thin yellow margins that will vary in size and shape and are most likely to be found on the older leaves. Septoria tritici blotch (which is considered rare in WA) is distinguished from the others when it develops small black fruiting bodies (pycnidia) in rows that are visible to the naked eye.

The fungal diseases survive on last seasons infected straw and readily infect new seedlings under conducive seasonal conditions. Development of both these diseases is favoured by frequent periods of wet/moist leaf surfaces. Trial results from the northern agricultural region have demonstrated yield losses of between 6 – 30% from the effects of leaf spot diseases."

Application of fungicide to manage these diseases is more likely to be economic when applied at or around flag leaf emergence (Z39). In wheat on wheat crop rotation situations where disease establishes early, a fungicide spray may need to be applied at early stem elongation (Z31 first node) to retard early disease development.  A second spray after three weeks or after flag leaf emergence will normally be required.

Departmental trials conducted in the northern agricultural region over previous years have shown that spraying for leaf spot diseases is more likely to be worthwhile when applied around the flag leaf emergence stage, to protect the flag and flag-1 leaves.  This applies particularly to crops in medium to high rainfall areas with a yield potential of over 2.5 t/ha situations and where there is evidence of increasing leaf spot activity down the canopy. 

More information on this and other pests is available through PestFax, which is sent direct to readers via e-mail, by requesting free subscription from PestFax@agric.wa.gov.au.  

Current and back issues can be found at: www.agric.wa.gov.au and search on the word PestFax.

This service relies on reports from its readership.  If you have recently observed or heard news of insect or disease pests in crops and pastures contact the editor: Peter Mangano at pmangano@agric.wa.gov.au