Black root rot, caused by a soilborne fungus, was first observed in Australian cotton in 1989. The disease has developed rapidly since then and now occurs in most of the cotton production area in NSW and Queensland. The fungus survives for long periods in the soil as very resilient, dormant spores that are produced abundantly on cotton roots. The severity of black root rot increases in proportion to the number of cotton crops, irrespective of fallows or rotations. The reproductive capacity and toughness of the spores make T. basicola virtually impossible to eradicate. Black root rot is favoured by cool temperatures and the infection of roots is, therefore, most severe at the seedling stage, causing stunted growth. No single control measure gives adequate protection against this pathogen and an integrated disease management approach is required.

The objectives of this research project were to evaluate novel and existing control measures for black root rot, conduct ongoing assessment of the impact of farming systems on black root rot and to consolidate and expand upon the existing disease management strategy for black root rot. A range of potential tools for control of black root rot were evaluated in glasshouse and field experiments. Key findings include:

• Confirmation that in-furrow application of the fungicide benomyl was ineffective in controlling black root rot (as previously indicated for other fungicides)

• Treatment of cotton seed with acibenzolar-S-methyl has potential for control of black root rot as part of an integrated disease management strategy

• The effectiveness of biofumigation against black root rot depends upon good growth, incorporation and breakdown of the biofumigation crop

• Delayed sowing has potential to avoid climatic conditions that favour black root rot and seedling disease and should be an effective control; the use of varieties with high fruit retention should enable delayed sowing without loss of yield potential

• Long-term rotation with non-host crops, such as cereals, has potential to decrease the population density of the black root rot pathogen sufficiently to control disease

• The host range of T. basicola was extended to include several weed species, indicating that effective control of weeds should help to reduce carryover of the black root rot pathogen

The integrated disease management strategy for black root rot has been modified to include the key findings of this research.