Kellie Penfold reports on research aimed at minimising the impact of root and crown diseases in the northern cropping zone.
The rapid adoption of controlled traffic dryland cropping, along with GPS and auto-steer technologies, may well provide one of the most effective solutions for minimising the yield-reducing effects of crown rot and common root rot.
Considered two of the most damaging diseases in winter cereals, crown rot (CR) and common root rot (CRR) are conservatively estimated to cost Australian graingrowers more than $78 million a year through reduced yields and quality.
Traditionally affecting areas where a hot, dry finish is experienced, such as northern NSW and southern Queensland, these fungal-based diseases are also progressively becoming a problem further south and even in the west with the increased stubble retention.
Researchers with the NSW Department of Primary Industries (NSW DPI) have been working with private agronomists and grower groups to establish recommendations for the management of CR and CRR by focusing on farming techniques, crop rotations, soil biology and the effects of stubble retention versus burning.
But simple trials started in northern NSW last year, expanding to cover a wider area this year, have already come up with one tool which appears to significantly reduce CR and CRR infection levels from one crop to the next.
Dr Steven Simpfendorfer, a member of the cereal disease management team at NSW DPI, Tamworth, says the trials illustrate that sowing in between previous winter cereal rows decreases the severity and incidence of CR and CRR in a following wheat crop.
Recent work by University of New England researcher Dr David Backhouse found that infection by Fusarium pseudograminearum (Fp), the fungus which causes CR, does not occur unless the plant comes in direct contact with a piece of residue harbouring the CR fungus.
Previous research had also shown inoculum levels of Bipolaris sorokiniana (Bs), the cause of CRR, are four times higher within cereal rows than within the inter-row space.
"In a no-till cropping system, inoculum of the CR and CRR fungi become concentrated in rows remaining from previous winter cereal crops. Conversely, cultivation results in greater dispersal of the stubble and more uniform distribution of pathogens throughout a paddock, even though incorporation can increase the rate of residue breakdown," Dr Simpfendorfer says.
Therefore, NSW DPI researchers wanted to test their theory that by using precision agriculture, the threat could be decreased. Working with agronomists and growers, they chose 12 wheat and barley paddocks in northern NSW for trials last year.
Each paddock was established under no-till using precision sowing equipment, with strips deliberately sown back on the previous cereal rows and the rest of the paddock sown between the previous rows.
Within each paddock, six sampling points were selected and marked at tillering. At harvest, wheat was sampled from these sites to assess the severity and incidence of CR and CRR.
"Row placements influenced the level of both diseases but had a greater effect on CR," says Dr Simpfendorfer. "Sowing between the previous cereal rows reduced the number of plants infected with Fp by 52 per cent. Averaged across all sites, disease severity decreased by 60 per cent.
"Actual severity was 27 per cent to 96 per cent lower than in those areas sown directly back on the previous rows. The variation in results appeared to be related to the extent of fragmentation of previous cereal residue."
Least disease developed in interrow sown crops where previous cereal rows remained upright with negligible disturbance, even after sowing in 2004.
Dr Simpfendorfer says the findings provide growers with another tool in a suite of management options to gain more control over CR and CRR.
"It is not a tool to allow growing continuous wheat without consequence, but it is another strategy that can be added to grow cereals with more confidence," he says. "It"s something practical that growers who already have the technology can try, because thanks to GPS and steering guidance they know where the crop was sown in previous years and they can now move the spacings to sow in between."
This year the research will become more specific with 40 trial paddocks in a wider area, and will incorporate use of the PreDicta B Root Disease Test, which measures fungal DNA levels in the soil using science developed by SARDI and commercialised by C-Qentec Diagnostics.
"There are still a lot of issues to figure out. At Walgett for example, they have the problem of where to put the nitrogen, as it is often pre-drilled before sowing. This means there is not a lot of room left between the previous cereal rows to establish the new crop," says Dr Simpfendorfer.
Another aspect to the research is rotations and the use of break crops, which is being done with CSIRO researchers.
It has already been found that there is more rapid breakdown of cereal residues under brassicas (canola and mustard) and faba beans thanks to their denser canopies, compared to chickpeas which have a slower growth.
Microbial changes within the soil and residue can also be beneficial to inoculum decline. Levels of Trichoderma, a group of fungi commonly associated with the biological control of pathogenic fungi, were consistently higher after brassicas than after chickpea or cereal crops within the trial plots.
"Ultimately the experiments demonstrate that canola and mustard provide an effective break crop for crown rot in northern NSW. The research has further highlighted the importance of canopy density in driving microbial breakdown of cereal residue which harbour the CR fungus, and the potential to manipulate residue biology to enhance the effectiveness and reliability of growing break crops."
GRDC Research Code DAN485
For more information: Dr Steven Simpfendorfer, 02 6763 1261, firstname.lastname@example.org
Package offer on Cereal Root and Crown Diseases, Ground Cover Direct, page 31
[Photo: Dr Andrew Verrel (NSW DPI) guides advisers through a replicated precision row plafcement experiment at Tamworth.]
[Photo: Wheat crop sown back onto previous cereal row.]
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