Trials suggest stubble impact on disease pressure
Applying fungicides to manage barley spot type net blotch (STNB) can be economic where there is high disease pressure, such as retained barley stubble, even in lower rainfall years.
New research has shown there is a potential 10 per cent yield gain from using fungicides under these circumstances in Western Australia’s medium rainfall zone (MRZ).
However, where stubbles are burnt before sowing and disease pressure is low, there may be no yield or economic advantage from using fungicides to control STNB in barley crops – when there is a dry finish to the season.
These are findings from 2015 trials established on 2014 barley stubble near Corrigin - investigating best practice foliar fungicide management for this stubble-borne disease in barley-on-barley sequences.
The trials were conducted by ConsultAg, with support from the Department of Agriculture and Food (DAFWA), and instigated and funded by the Grains Research and Development Corporation’s Kwinana West Regional Cropping Solutions Network (RCSN) group.
GRDC Western Regional Panel member and barley grower Andy Duncan said the incidence of barley STNB in WA's MRZ had increased in recent years as growers planted more barley, including consecutive barley crops, on the back of high profits and lower rotation risks.
“However, varieties currently grown in this system are either susceptible or moderately susceptible to this disease and management can be difficult, especially in retained stubble systems,” he said.
“The RCSN research project’s objectives included improving understanding of the interactions of STNB, stubble and fungicides on the impact of disease, yield and profitability of barley-on-barley rotations.
“The Corrigin trial site was planted to Scope barley in 2015 on burnt and retained stubble areas and 14 different fungicide treatments were assessed.”
Ashton Gray, of ConsultAg, said the treatments included single application at growth stage Z31 (first node formed) and multiple applications at Z31 and Z37 (flag leaf visible).
The site received 190mm of growing season rainfall in 2015, which was 90mm below the long-term average, and a dry spring limited late season disease development.
“Overall, the trial found crop yields were consistently about 0.4 tonnes per hectare higher where stubbles were burnt and disease pressure was lower, compared with retained stubble areas, irrespective of the fungicide treatment,” Mr Gray said.
“Disease severity was also much reduced where stubbles had been burnt, especially at the early stages of plant growth, and screenings were lower compared with retained stubble areas.
“However, further evaluation is needed as this result may have been affected by soil water relations, frost and/or nutrition, and solely burning stubbles to manage this disease in 'typical' seasons may not provide the best yields or returns.”
Mr Gray said the trial highlighted that fungicide use for barley STNB control could contribute significantly to improving grain quality (fewer screenings) as well as grain yield.
"In the retained stubble trials, some fungicide treatments kept screenings at the same level as the burnt stubble trial," he said.
"In a wetter year, yield responses are likely to be much higher and a two-spray fungicide strategy might be needed where stubbles are retained - although there is no point applying the first fungicide before the five-leaf stage."
The trial work is being repeated in 2016 to get a better understanding of the responses to stubble management, fungicides and disease pressure in different seasons in the MRZ.
Ashton Gray, ConsultAg
08 9622 5095, 0429 930 074
Andy Duncan, GRDC Western Regional Panel
0428 996 334
Natalie Lee, Cox Inall Communications
08 9864 2034, 0427 189 827
GRDC Project Code TAR00006