Management to reduce Rhizoctonia and crown rot
Options to reduce Rhizoctonia include:
- choosing a grass-free canola, pulse or pasture;
- good summer and autumn weed control;
- sowing into warm soil;
- disturbing soil below the seed;
- avoiding herbicide damage;
- ensuring adequate nutrition;
- considering in-furrow fungicides and/or seed treatments; and
- clay delving in non-wetting sands.
Options to reduce crown rot include:
- choosing a break from cereal crops and controlling grass weeds;
- early canopy closure in break crops to enhance stubble breakdown;
- selecting a less susceptible wheat or barley variety;
- sowing cereals between the rows of the last cereal crop;
- avoiding cultivation/stubble burial close to sowing a cereal crop;
- matching nitrogen to season potential; and
- ensuring adequate nutrition.
Cereal root diseases cost grain growers in excess of $200 million per year in lost production, yet much of this can be prevented
Crown rot disease in wheat.
PHOTO: Sharon Watt
PreDicta® B is a DNA-based soil testing service provided by the South Australian Research and Development Institute (SARDI), and supported by the GRDC, that identifies which soil-borne pathogens pose a significant risk to broadacre crops prior to seeding.
PreDicta® B includes tests for:
- cereal cyst nematode (Heterodera avenae);
- take-all (Gaeumannomyces graminis var. tritici (Ggt) and G. graminis var. avenae (Gga));
- Rhizoctonia barepatch (Rhizoctonia solani AG8);
- crown rot (Fusarium pseudograminearum and F. culmorum);
- root lesion nematode (Pratylenchus neglectus and P. thornei);
- stem nematode (Ditylenchus dipsaci); and
- blackspot of peas (Mycosphaerella pinodes, Phoma medicaginis var. pinodella and Phoma koolunga).
Growers can access PreDicta® B diagnostic testing services through a SARDI-accredited agronomist. The agronomist will interpret the results and provide advice on management options to reduce the risk of yield loss.
About 1700 agronomists and consultants across Australia have been PreDicta® B accredited through SARDI’s annual Agronomist Root Disease Risk Management training courses, which are supported by the GRDC.
SARDI processes PreDicta® B samples weekly from February to mid-May (less frequently at other times of the year).
Recommended PreDicta® Bsampling strategy for crown rot
- PreDicta® B is a valuable tool for quantifying the level of risk for crown rot (and other soil-borne pathogens) prior to sowing. However, this requires a dedicated sampling strategy and is not a simple add-on to a soil nutrition test.
To sample correctly, growers and advisers should do the following:
- In the southern and western regions, collect three cores of one-centimetre diameter and 10cm deep from each of 15 different locations within the target paddock or production zone.
- In the northern region, collect two cores of 1cm diameter and 15cm deep from each of 15 different locations within the target paddock or production zone.
- Take the soil cores along the rows of the most recent cereal crop, if still visible, and retain any stubble collected by the core (most soil-borne pathogens are concentrated under the rows of the last cereal crop).
- If the rows cannot be seen, take the cores at random.
- Add one piece of cereal stubble (two pieces in the northern region), if present, to the sample bag at each of the 15 sampling locations to improve the detection of crown rot. Each piece should be a single dominant tiller, 5 to 7cm long, from the base of different plants, and include the crown.
- The maximum sample weight should not exceed 500 grams.
- Significant stubble disturbance through harrowing, cultivation or mulching increases the risk of crown rot development if the stubble is infected with Fusarium. Collection of soil samples prior to stubble disturbance is likely to underestimate the crown rot risk.
- Record all sampling details listed on the sample bags provided in the PreDicta® B kit.
High disease-risk situations, where soil testing may be considered or targeted, include:
- intensive cereals (cereal following cereal)
- lower-rainfall regions: Rhizoctonia, crown rot, Pratylenchus; and
- higher-rainfall regions: take-all, Pratylenchus;
- cereal following a grassy pasture: Rhizoctonia, crown rot, Pratylenchus;
- intensive wheat/chickpea rotations: Pratylenchus (northern region);
- susceptible/intolerant cereal varieties grown on stored moisture: crown rot, Pratylenchus (northern region);
- durum wheat: crown rot (southern and northern regions);
- paddocks with unexplained poor yield from the previous year;
- newly purchased or leased land with no disease history;
- bare patches, uneven growth, whiteheads in previous crop;
- canola, wheat, barley rotations: Pratylenchus (western region);
- surviving grass weeds and volunteer cereals: Rhizoctonia, crown rot, take-all, cereal cyst nematode;
- wild radish and turnip: P. neglectus; and
- decaying weeds at sowing (for example, large capeweed plants): Pythium.
Table 1 shows the frequency of PreDicta® B paddock samples from 2015 with medium-to-high disease-risk ratings. In the southern and western regions, Rhizoctonia, crown rot and take-all are prevalent, with P. neglectus and P. quasitereoides also common at medium-to-high levels in the west (P. quasitereoides levels are reported in the ‘test under development’ section of the report without risk categories). In the northern region, medium-high levels of P. thornei and crown rot are evident in many of the samples.
Table 1 The frequency of PreDicta®B paddock samples in 2015 with medium/high disease risk for the major cropping regions in Australia.
||Number of samples
|Cereal cyst nematode
| P. neglectus
*Provisional risk categories
Note: it is assumed that paddocks tested will have a bias towards higher levels.
In the PreDicta® B soil test reports, both the pathogen levels and the associated disease-risk categories are listed. In addition to this, the range of potential yield loss is described for each pathogen that is detected. These ranges are presented in Table 2 and continue to be reviewed by pathologists nationally.
Table 2 Potential grain yield losses in wheat with medium/high disease risk levels.
| Cereal cyst nematode
| Crown rot
| Crown rot (durum)
| Southern region
| Western region
I = Intolerant, MT = Moderately tolerant
*Provisional risk categories
Note: losses will be in the higher range when seasonal conditions are conducive to disease
Crown rot in winter cereals fact sheet
Analysis underlines value of PreDicta® B for cropping decisions
Rain prompts disease watch
GRDC Project Code