Australian cotton growers are exposed to and manage a variety of cotton diseases. This project had a number of objectives to address knowledge gaps and obtain data to improve the management of Fusarium wilt, Verticillium wilt and reniform nematode.

Many of the current strategies to manage Fusarium wilt have been developed as a result of the project work carried out at Mr Graham Clapham’s property ‘Cowan’. The “Cowan” trial site is recognised by the cotton industry as a high disease incidence site, providing unbiased information on disease management practices. Some specific outcomes include: (i) the identification of some agricultural practices, such as crop rotations, that may reduce the incidence of the disease. These practices reduce populations of Fov in the soil and increase yield potential, thereby contributing to the sustainability of cotton production.

A published PCR based diagnostic assay detects two of the three Australian strains of Fov. Testing in this project confirmed published results as well as confirming that the test detects the “Mungindi” strain. This test has enabled faster confirmation of Fusarium wilt to industry. Faster detection allows for faster implementation of strategies to manage this disease.

Nutrition trials where three cultivars differing in Fusarium resistance were grown highlighted the importance of planting the highest F. rank variety in Fusarium infested fields to maximise yield. Interestingly, fertilising with NPK had no effect on seed cotton yield or disease severity, except for one exception where the addition of P and K had a negative effect on yield for the lowest F. ranked cultivar compared to K alone. The lack of response is curious as the field plot was planted to crops for several seasons without fertiliser inputs so as to deplete the nutrition. This was done to enable the influence of nutrient inputs on disease to be assessed in a controlled experiment. Results indicate that for Sicot 74BRF and Sicot 75BRF there was no benefit to applying N, P or K on seed cotton yield or disease severity. Further work is needed to better understand fertilisation of soil, nutrient uptake and nutrient requirements for maximising yield.

Verticillium wilt caused by Verticillium dahliae, although present in Queensland has rarely been detected during annual disease surveys and historically has not caused significant yield reductions. However, in the 2014/15 season, the highly virulent strain VCG 1A of V. dahliae was detected for the first time, causing significant disease in susceptible varieties. Following molecular characterisation and VCG analysis of V. dahliae isolates it is known that three strains of the pathogen are present in Australian fields. The ‘defoliating’ strain VCG1A and ‘non-defoliating’ strains VCG 2A and 4B were identified using specific primers and VCG analysis.

Pathogenicity studies determined that VCG’s 1A and 2B are highly pathogenic and VCG4B is mildly pathogenic, on cotton. Current management strategies such as crop rotation with non-hosts are not successfully managing the highly virulent strains and further research into management strategies are required.

Seed plating studies showed that V. dahliae was not detected in any of the seed, hand-picked from plants showing wilt symptoms from the CSIRO breeding program. This data suggests that Verticillium is not seed-borne in Australian cotton. Testing is on-going.

In 2012 reniform nematode was detected for the first time in the Dawson/Callide region of Central Queensland. This nematode was determined to be widespread in this region causing up to 40% yield reduction. In this project, monitoring of fields was a non-destructive way of providing an indication of possible nematode problems and provided useful information towards developing economic threshold levels of reniform nematode in Australian cotton. Management strategies were also investigated such as crop rotation and seed treatments.

Data from three seasons suggest that a population of 1000 reniform /200mL of soil post-harvest results in a 10% yield reduction. Deep coring to 100 cm has shown that reniform are present at depth, thereby providing a reservoir of nematodes that may reinfest the planting zone when cotton is sown. Corn and sorghum are non-hosts of reniform and significantly reduce soil populations compared to cotton and are therefore good rotation options for growers to manage this pest. However even after two rotations out of cotton, populations returned to high levels when cotton is grown. Seed treatments tested in this project had no significant effect on soil population of reniform. Multiple strategies will be required to manage this pest.

The research results obtained during this project have been widely disseminated throughout the industry.