Disease is usually a problem in wet years, but this year Spot Form Net Blotch has been prevalent in barley crops in Northern NSW and into Queensland.
Grains Research and Development Corporation (GRDC) Crop Protection Manager - North, Vicki Green said its appearance during a dry year meant growers had to make difficult decisions on whether to treat the disease with fungicides or not.
"We've had such a dry growing season but surprisingly we're seeing Spot Form Net Blotch in quite a number of farming paddocks," Ms Green said.
"It has an impact on yield but when we have crops that are really struggling with insufficient rainfall, growers have to make the call as to whether they're going to get an economic response from spraying out the disease."
She said although wetter years were usually associated with disease, Spot Form Net Blotch seemed to take hold when plants were stressed.
"That's what we're seeing this year because plants are stressed by a lack of moisture," Ms Green explained.
"It is carrying over in stubble and that inoculum is just not breaking down in the dry conditions we are experiencing."
She said growers were advised to look at their rotational options and avoid growing barley on barley, yet this season the disease had also been spotted in paddocks that had not been planted with barley for a number of years.
"It just shows how complex the interaction between the disease and the environment is," Ms Green said.
She said when deciding whether to spray growers should also consider the end market for the product.
"Some people are cutting crops for silage which will restrict the fungicide products that can be used for disease control due to their long withholding periods," Ms Green advised.
Croppa Creek agronomist, Doug McDougall said in his district the disease had been easy to find in any barley on barley country.
"Some early preventative fungicides went out when the crop condition was reasonable but in the last two to three weeks a lot of that crop condition has declined," Mr McDougall said.
"It's not economically viable in most cases to go and control because crops are running out of moisture.
"We're not really sure whether it will get to harvest stage."
He said the disease had been spotted in both dryland and irrigated crops.
"It can have a 20-30 per cent impact on yield if left untreated, possibly more on a dry finish," Mr McDougall said.
"There's a lot of economic solutions out there and it's a reasonably easy decision in most years to apply fungicide, it's just these dry years where it's hard to justify spending any money on the crop."
Sam Conway farms properties at both Moree and Gunnedah and has seen an equal prevalence of the disease in both regions.
"It has been pretty surprising, around Moree we have Spot Form cycling on dew, even though we haven't really had any rainfall," Mr Conway said.
"There's been more activity on country with residual stubble but we are seeing a lot of Spot Form cycling on country that has been clean of barley for a couple of years."
He said in Moree, where there was limited yield potential, they had sprayed once but wouldn't again without substantial rain forecasted, whereas in Gunnedah they would put out a second treatment.
Mr Conway said they had previously tried preventative seed coatings but they hadn't had much of an impact and he thought rotations and varieties were more likely to affect susceptibility.
"There's also a big difference with varieties, Planet seems to have been very susceptible to Spot Form, it's shown up in Planet more than in Spartacus or Commander."
"That's probably the first downside we've seen with Planet since we started growing it three years ago."
