For the first time since 2001, NSW Department of Primary Industries (DPI) has identified significant levels of the leaf disease, septoria tritici blotch (STB), in commercial wheat crops in NSW.
Speaking during the 2016 Henty Farm Machinery Field Days, DPI plant pathologist, Andrew Milgate, said cases of STB infection were confirmed in Narromine, Forbes and Young district wheat crops and recently STB was confirmed in a Coolamon wheat crop.
“The severity of infection is concerning and we urge growers and agronomists to be vigilant and maintain crop inspections to determine if STB or other diseases are present,” Dr Milgate said.
“Mild, wet conditions continue to favour disease development - we advise growers obtain correct identification of any pathogen and take actions recommended by an agronomist.
“While STB has been uncommon in NSW for more than a decade, it has become a significant foliar disease in the high rainfall regions of Victoria, South Australia and Tasmania.
“Re-emergence of STB in NSW poses a threat to early sown crops in high rainfall areas - risk of widespread infection and subsequent crop loss in low to medium rainfall areas of NSW remains low.”
In most cases the disease has occurred alongside yellow leaf spot (YLS) and in some the combined severity of infection has warranted advice to spray with fungicide to prevent further losses of leaf area.
Dr Milgate said changes in virulence to variety resistance and the development of fungicide resistance in the Australian STB population was of particular concern.
“In the last 12 months, triazole fungicide resistance has been confirmed in additional isolates collected from Victoria, South Australia and Tasmania.
“Now isolates containing resistant mutations have been confirmed in NSW,” he said.
Integrated approach to leaf disease control
The NSW wheat belt has seen great rain during the growing season: and with the prospect of an outstanding 2016 grain harvest, despite some loss due to water logging and flooding, NSW DPI Wagga Wagga plant pathologist, Andrew Milgate, is advising NSW wheat growers to take steps to mitigate further loss by treating crops likely to be infected by septoria tritici blotch (STB).
Be vigilant, Dr Milgate warns wheat growers.
“Early screening of resistance levels shows most fungicides will be effective in the paddock and to avoid further losses in efficacy growers are urged to use multiple strategies against STB,” Dr Millgate said.
“An integrated approach to disease control should include mixes or rotations of fungicides, crop rotation and avoid susceptible cultivars to reduce inoculum.
The severity of infection is concerning and we urge growers and agronomists to be vigilant and maintain crop inspections to determine if STB or other diseases are present.
“Integrated disease management aimed at reducing the disease burden on crops will lift yields and help prevent fungicide resistance.”
It is critical growers adopt strategies to reduce selection rates of further mutations, to maintain and extend the useful life of currently available fungicides, according to Dr Millgate.
“One strategy which is expected to slow the selection of strains with higher resistance is to mix or alternate different azoles,” he said.
“In crops where two fungicide applications are used, different actives should be used each time.”
Dr Millgate said STB infections produce distinctive black fruiting bodies in necrotic (dead) lesions, which develop three to four weeks after infection.
- STB information and management advice is available from the Grains Research and Development Corporation website.