Rhizoctonia fungicide responses have been investigated in two South Australian Grain Industry Trust (SAGIT) funded projects in the South Australian Mallee, finding that applying fungicide to control rhizoctonia root rot increased barley yield by 0.3 tonnes per hectare at Wilkawatt in 2015 even though growing season rainfall was only 114mm.
The trial, led by South Australian Research and Development Institute (SARDI) Soil Biology and Diagnostics research leader Dr Alan McKay, in collaboration with Dr Jack Desbiolles from the University of South Australia (UniSA), was designed to provide an understanding of factors that affect a crop’s response to liquid fungicide banded in-furrow.
A second SAGIT and GRDC-funded project, also managed by SARDI and UniSA to examine Rhizoctonia control in the Mallee, found that triple-disc openers can match knife-points in yield response to fungicide applied to control the disease.
“Previous SAGIT and GRDC funded research has shown that new fungicides can provide useful control of rhizoctonia root rot, and that yield responses increased when growing season rainfall increased from 200 to 400 mm rainfall.” Dr McKay said.
The soil opener project included trials at Geranium, Lameroo, Parrakie and Moorlands in 2014 and 2015, which were both low rainfall seasons, and compared a range of disc seeder treatments with knife points. The work was conducted with UniformTM fungicide.
“In 2014 triple disc openers at Parrakie gave the best response to fungicide, with a yield gain of 0.22t/ha in wheat,” Dr McKay said.
“At Geranium the results were similar for triple disc and knife point at about 0.14t/ha in 2014 and 0.22t/ha in 2015.”
At the Lameroo trial, conducted in 2014, there were no yield responses to fungicide in wheat and this appeared to be correlated with high levels of Pratylenchus neglectus, leading to the hypothesis that the root lesion nematode was affecting the fungicide response.
“The effects of time of sowing and Pratylenchus neglectus on the yield response to fungicide have previously not been well understood.”
The Wilkawatt project followed in 2015 and studied the effects of time of sowing and two levels of Pratylenchus neglectus on wheat and barley treated with Uniform® fungicide banded at 200 millilitres per hectare above the seed and 200mL/ha below the seed.
“We found that while the time of sowing had the greatest overall effect on the crop, with earlier sowing resulting in higher yields, the time of sowing did not influence fungicide control of Rhizoctonia,” Dr McKay said.
“Regardless of the time of sowing and P. neglectus levels (two or 10 nematodes per gram of soil), the fungicide provided a positive yield response in barley, averaging 0.3t/ha or 18 per cent.
“In wheat, the fungicide provided no yield benefit where there were an average of 10 P. neglectus/g soil, a moderately low level for the southern region. However, in the low-nematode treatment, wheat yield increased by 0.2t/ha (12 per cent) when the fungicide was applied.
“This indicates that applying fungicide where there are significant levels P. neglectus is not likely to be cost-effective in wheat during a low rainfall growing season.”
“Where PREDICTA B testing has shown a risk of Rhizoctonia, growers can maximise their return on investment in fungicide by prioritising application on barley, followed by wheat where root lesion nematode levels are low,” Dr McKay said. The liquid fungicide application in-furrow also lends itself to variable rate application in paddock soil zones found at greater risk, to reduce input cost per paddock ha.
“Responses are also likely to be greater as growing season rainfall increases from 200 to 400mm, and where there is stored moisture from summer rains.”