RELENTLESS hot and dry seasonal conditions are threatening to strip millions of dollars in yield from winter cereal crops across the northern region by exacerbating the effects of the fungal disease crown rot.
Crown rot is caused by the fungus Fusarium pseudograminearum and is one of the most serious disease threats to winter cereal crops in Australia.
It's important to remember that infection requires direct contact with the plant and most infection points are below the ground.
NSW Department of Primary Industries (NSW DPI) senior plant pathologist Dr Steven Simpfendorfer said the expression of crown rot was widespread this season and was likely to significantly affect yields in some areas, particularly in durum wheat crops.
"There are several factors that have exacerbated the expression of crown rot this year. Generally speaking starting soil moisture levels were significantly lower than in 2012 but an even bigger issue has been the above average temperatures and lack of rainfall during winter, particularly during the grain-fill period," Dr Simpfendorfer said.
"Previous trials have shown that with high infection, yield losses can be more than 50% but importantly, even at low inoculum levels, you can still get yield losses of 25% if the season runs against you.
"The conditions have been shocking this year - we've been sitting on high infection levels for a number of years but until now the effect has been somewhat buffered by soil moisture levels and milder temperatures during grain-fill.
"This year many crops have simply run short of stored moisture and plants have had to expend additional energy to uptake limited moisture for grain fill from a greater depth in the soil. Increased evaporative demand with hotter temperatures during grain-fill has also increased the expression of crown rot this season."
Dr Simpfendorfer said moisture stress during the grain-fill period encouraged the fungus to proliferate at the base of the tillers blocking up the vascular system and destroying some of the lower nodes prompting the development of whiteheads.
Depending on how far through grain formation the crop is this can mean no grain or impact heavily on screenings.
Growers are being urged to monitor crops closely for signs of the disease so appropriate risk management strategies can be put in place to reduce the pathogen's survival and infection of the 2014 winter crop.
The Grains Research and Development Corporation (GRDC) advises growers to assess crown rot risk by checking for browning of the stem base or by taking soil and stubble samples for analysis.
According to the GRDC factsheet, Crown Rot in Cereals, the most effective way to reduce yield loss is by maintaining crown rot inoculum at low levels, particularly through a grass-free break from winter cereal cropping.
However, drier in-crop conditions during break crops in 2012 and 2013 is reducing the efficacy of these breaks with the crown rot fungus surviving longer in infected cereal stubble.
Other risk mitigation strategies include paddock selection based on previous crown rot infection levels, selection of appropriate cereal crop and variety to disease prevalence and susceptibility, and strategic sowing times.
The GRDC has also been supporting research to identify new germplasm for plant breeders that will allow future wheat and barley varieties to yield well under crown rot pressure.
Dr Simpfendorfer said effective management of the pathogen's on-going survival and infection levels was a balancing act between inoculum levels and soil water.
"Often in management we focus on getting rid of infected stubble and therefore inoculum breakdown which is often to the detriment of soil water and this can actually make the crown rot worse," he said.
"It's important to remember that infection requires direct contact with the plant and most infection points are below the ground.
"So although cultivation can accelerate stubble breakdown, it can also distribute infected stubble throughout the soil as well as hindering water infiltration.
"The key message for growers is just to leave infected stubble alone - that's why inter-row sowing especially in no-till systems works so well as part of an integrated disease management program."
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