Agriculture Victoria researchers are warning farmers that varieties they consider resistant to foliar fungal diseases such as stripe rust may be more at risk than first thought.
Plant pathologist Grant Hollaway said the University of Sydney had detected seven different strains of stripe rust disease last year, including an old strain, which meant the resistance ratings needed to be considered according to the strain.
He said the industry was providing two ratings this season, one reflecting resistance to the more common strains of the disease and one judged against the old strain.
"A dual rating is provided, where a variety can be moderately resistant / susceptible according to the strain of rust," Dr Hollaway said.
Together with fellow Ag Vic research Mark McLean, Dr Hollaway said while the previous year had been fantastic for crop production it also was conducive for disease.
The pair warned the risk of fungal disease this year will be higher, particularly for the diseases that thrive on a 'green bridge' over the summer period.
Dr Hollaway recommended that growers have paddocks clean of volunteers and other weeds for a minimum of four weeks to lower the risk of fungal disease carryover.
Speaking at a Grains Research and Development Corporation update in Bendigo last month, Dr Hollaway said Ag Vic trials had showed yield losses of up to 50 per cent last year due to foliar diseases in untreated plots.
He said farmers needed to pay close attention to rotations and crop selection to avoid an unhealthy reliance on fungicides should the season prove favourable for disease this year.
"Disease management plans should consider paddock and variety selections and where the risk warrants it, the proactive and prudent use of fungicides," Dr Hollaway said.
However, he cautioned against the prophylactic use of fungicides, saying it led to a greater risk of resistance to a relatively small group of effective products.
On the barley front, Mr McLean said both spot form and net form of net blotch (SFNB and NFNB) had been common last year.
He said many plants displayed symptoms of infection from both diseases.
In trials, yield loss varied between 9pc and 20pc, with the higher losses found in susceptible varieties.
"These losses show that susceptible varieties, like Planet, should be managed for multiple foliar diseases in favourable seasons to minimise losses," Mr McLean said.
On the oat front, Dr Hollaway said red leather leaf was proving an increasing issue, particularly in medium to high rainfall zones, with some level of the disease found in 80 per cent of crops surveyed in Ag Vic oat crop research.
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