Andrew Verrell, Steven Simpfendorfer, Paul Nash and Kevin Moore
NSW Department of Primary Industries, Tamworth Agricultural Institute

Take home messages

• Leave last years cereal residue standing
• Residue sweeping (straw whippers) can reduce the incidence and severity of Crown rot
• Sowing between previous cereal rows can reduce the incidence and severity of Crown rot and increase grain yield

Background

The Crown rot (CR) fungus Fusarium pseudograminearum (Fp) survives as mycelium in winter cereal and grass weed residue. Incidence and development of CR are influenced by the interaction between soil and plant water potential (Papendick and Cook 1974; Beddis and Burgess 1992; Verrell 2004), soil nitrogen (N) (Wildermuth et al. 1997a; Felton et al. 1998; Verrell 2004), variety and inoculum level. The disease can kill tillers and whole plants (Wildermuth et al. 1997c) and can also lead to whiteheads – a symptom associated with small or no grain (Burgess et al. 2001). CR has increased in the GRDC northern region since 1985 and this appears linked to the use of susceptible varieties and to the expansion of residue retention systems under zero-tillage (Burgess et al. 2001). Importantly, Dr David Backhouse (UNE) has shown that infection does not occur unless a piece of residue harbouring the CR fungus touches the plant.

The Common root rot (CRR) fungus Bipolaris sorokiniana (Bs) can persist as mycelium in crop and grass weed residues but survives mainly as conidia in soil (Weise 1987). When N is not limiting, CRR can cause yield loss through early infection and reduced tiller density (Verrell, 2004). Severity of CRR was lower where stubble was removed compared with retaining stubble and was also lower under zero-tillage (Wildermuth et al. 1997b).  Reis and Abrao (1983) found more conidia of Bs in soil under conventional tillage versus zero-tillage. Wildermuth et al. (1997b) found Bs inoculum levels were four times higher in soil within previous cereal rows than between previous cereal rows.

These findings suggest that inoculum of CR and CRR should remain concentrated in the previous cereal rows, providing the cereal residue is not disturbed and redistributed through cultivation. This raises the question: Can this spatial distribution of inoculum be used to reduce disease in a following wheat crop by: (i) deliberately sowing into the inter-row space between the previous stubble rows, and (ii) by manipulating surface residue?

Methods

A replicated field experiment was conducted in 2004 at Tamworth to examine the effect of row placement and stubble management on CR, CRR and yield of durum wheat (cv Bellaroi). The trial was sown into 2003 durum stubble. This stubble was either retained in tact, slashed and removed, or moved sideways with straw whippers. The 5- row plots were either sown between the 2003 rows or on top of them. Pre-sow sampling of the 2003 stubble showed background levels of Fp ranged from 12-60% (mean 40%).  Prior to harvest, severity (symptoms) and incidence (recovery of pathogens) of CR and CRR were determined by counting whiteheads and by plating crowns plus subcrown internode tissue.

Findings

Plant density (mean 63 plants/m²) and tiller density (mean 260 tillers/m²) were unaffected by any of the treatments. Recovery of Bs was very low across this site and was unaffected by either row placement or stubble management (mean 6%). Recovery of Fp was reduced where straw whippers were used (Figure 1a) and where wheat was sown between the previous cereal rows (Figure 1b) compared to other treatments. The high incidence of Fp were the stubble was removed is possibly due to excess fragmentation of the straw due to slashing.

Whitehead assessments were made at early grain-fill and were lowest where stubble was removed with straw whippers (Figure 2a) and where wheat was sown between the previous rows (Figure 2b).

Grain yield was not affected by stubble management practices but responded to row placement with a significant increase in yield when wheat was sown between the previous cereal rows (Figure 3a). Grain yield showed a strong linear decline as whiteheads increased (Figure 3b).

Conclusions

The conditions of this experiment (i.e. durum on durum) were very conducive for CR and would approach a worst case scenario for most wheat growers. Even under such high disease pressure, sowing between the previous cereal rows reduced incidence of Fp and whiteheads and this increased grain yield by 9%.

Using straw whippers to ‘sweep’ away residue in front of the ground engaging gear also reduced the incidence of Fp and whiteheads.

This single experiment has shown the potential for precision planting and residue manipulation to reduce disease in a zero-till system. Further research will look at integrating the spatial distribution of inoculum with crop sequencing, water and N management and varietal selection.

Hopefully this will prompt growers and agronomists to evaluate this under commercial conditions.

Acknowledgements

This work was funded by GRDC.

We gratefully acknowledge technical assistance provided by Karen Cassin, Robyn Shapland, Richard Morphett, Chris Bowman and Kay Warren in conducting this research.

Contact Details

Dr Andrew Verrell,
Ph: 67631213, Fax: 67631222,
email: andrew.verrell@agric.nsw.gov.au

References

Beddis, A.L., and Burgess, L.W. (1992). The influence of plant water stress on infection and colonization of wheat seedlings by Fusarium graminearum Group 1. Phytopathology 82, 78-83.

Burgess, L.W., Backhouse, D., Summerell, B.A., and Swan, L.J. (2001). Crown Rot of Wheat. In: Fusarium: Paul E Nelson Memorial Symposium. Summerell, B.A., Leslie, J.F., Backhouse, D., Bryden, W.L., and Burgess, L.W. (editors), APS Press, The American Phytopathological Society, St. Paul, Minnesotta, 271-294.

Felton, W.L., Marcellos, H., Alston, C., Martin, R.J., Backhouse, D., Burgess, L.W., and Herridge, D.F. (1998). Chickpea in wheat based cropping systems of northern New South Wales. II. Influence on biomass, grain yield, and crown rot in the following wheat crop. Australian Journal of Agricultural Research 49, 401-407.

Papendick, R.I. and Cook, R.J. (1974). Plant water stress and development of Fusarium foot rot in wheat subjected to different cultural practices. Phytopathology 64: 3, 358-363.

Reis, E.M., and Abrao, J.J.R. (1983). Effect of tillage and wheat residue management on the vertical distribution and inoculum density of Cochliobolus sativus in soil. Plant Disease 67, 1088-1089.

Verrell, A.G. (2004). Water, nitrogen, crown rot and common root rot interact to limit wheat production in northern NSW cropping systems. PhD thesis, The University of Sydney.

Weise, M.V. (1987). Compendium of Wheat Diseases. 2^nd edition. The American Phytopathological Society, Minnesota, USA.

Wildermuth, G.B., Thomas, G.A., McNamara, R.B., and Sparks, T.M. (1997a). Nitrogenous fertiliser increases severity of crown rot. Proceedings, 11^th Biennial Conference of the Australasian Plant pathology Society, 167.

Wildermuth, G.B., Thomas, G.A., Radford, B.J., McNamara, R.B., and Kelly, A. (1997b). Crown rot and common root rot in wheat grown under different tillage and stubble management treatments in southern Queensland. Australian Soil and Tillage Research 42, 211-224.

Wildermuth, G.B., Thompson, J.P., and Robertson, L.N. (1997c). Biological change: diseases, insects and beneficial organisms. In: Sustainable crop production in the sub-tropics: An Australian perspective. Clarke, A.L., and Wylie, P.B. (editors), QDPI, Brisbane, Queensland, 112-130.