SM NEATE and DK ROGET

CSIRO, Land and Water and Cooperative Research Centre for Soil and Land Management, PB No 2, Glen Osmond, SA 5064, Australia

Background and objectives
The three major root diseases of cereals in southern Australia are, in order of importance, take-all caused by Gaeumannomyces graminis var. tritici, rhizoctonia bare patch caused by Rhizoctonia solani AG-8, and cereal cyst nematode (CCN), Heterodera avenae.

Low-cost systems of sustainable disease control have developed in low-rainfall cereal production systems in southern Australia because low yields (an average of 1.8 t/ha) and low returns (an average of less than $US 140/t) do not allow for high-value applications of pesticides, nutrients or amelioration treatments.

Materials and methods
Long-term experimental field sites were chosen to be representative in climate and soil type of the majority of the cereal-growing areas of southern Australia. Avon, started in 1978, has a solonized brown soil with a 320 mm annual rainfall (260 mm in growing season). Treatments were 2-year rotations of wheat-wheat, grassy pasture-wheat, medic pasture-wheat, peas-wheat and oats-wheat in a factorial design with tillage treatments of direct drilling and conventional cultivation. Kapunda, started in ....

Conventional cultivation consisted of three cultivations with 15 cm shares before sowing, reduced cultivation was one cultivation with 15 cm shares before sowing, and direct drilling was no cultivations prior to seeding and sowing with a 1 cm or less wide point.

Annual measurements of root disease, plant growth and yield were made.

Results and conclusions
Multiple cultivations are the traditional way of controlling rhizoctonia bare patch. This has led to soil erosion and soil structural decline being a major problem. The increase in this disease with reduced tillage prevented widespread adoption of conservation farming practices. A direct-drill system that reduces rhizoctonia root rot to levels equivalent to cultivation has been developed. It is based on (i) 3 weeks prior to sowing the chemical removal of volunteer plants that germinated with o....

Management of take-all and CCN is based on rotation with non-host crops or the use of volunteer legume-based pastures where grasses are chemically removed early in the season. Both diseases decline under fallowing and non-hosts, but fallowing is discouraged because of its detrimental effect on soil structure.

The management of CCN has been significantly improved by the development of resistant and tolerant cereal cultivars. These new cultivars have replaced the use of nematicides which were in common use during the 1980s. There is no useful resistance to rhizoctonia root rot or take-all diseases in the major cereals.

An area of major research effort is in soils suppressive to root diseases of cereals. After 8-10 years of stubble retention and cropping, both rhizoctonia bare patch and takeall declined in field plots to insignificant levels and have remained there since, despite fluctuating levels in the surrounding farmers' fields [2]. Investigation of the soil revealed the development of microbiologically based disease suppression [3]. Unique characteristics of this suppression are that it is not associated with

References
1. MacNish GC, Neate SM, 1996. Plant Disease 80, 965-971.
2. Roget DK, 1995. Australian Journal of Experimental Agriculture 35, 1009-1013.
3. Wiseman BM, Neate SM, Ophel-Keller K, Smith SE, 1996. Soil Biology and Biochemistry 28, 727-732.