14 IREC Farmers' Newsletter No. 198 — Spring 2017 A biofumigant crop growing in northern NSW as part of CRDC Verticillium wilt management research. The crop will be green manured in mid- August and cotton planted at the start of October . PHOTO: Geoff Hunter, CottonInfo Namoi region. Although biofumigation does not eradicate the disease from the soil it does reduce disease severity enough to warrant its use. Woolly pod vetch has been used successfully as a biofumigant for black root rot of cotton in the USA and Australia, and it has the added benefit of providing substantial amounts of nitrogen for the following cotton crop. Integrated disease management Rice in the rotation could be an option for some cotton fields in southern NSW to reduce black root rot spore loads. Layouts and soil type needs to be suitable for this to be a practical option. The rice crop should be followed by a cereal crop (not fully irrigated) and a summer fallow over summer before a return to cotton. Summer flooding of fields for 30 days when daytime temperatures are above 30 °C may be a good alternative option for some growers. The use of biofumigant green manure crops also has merit. Woolly pod vetch has been the favoured option as it provides significant nitrogen to the following crop and is not a black root rot host. Other crops such as canola, mustard and forage sorghum need further investigation and research. The best option — don’t get to this point! Use a sensible rotation with a break of non-black root rot hosts such as cereals and clean fallow periods. It is important to have an integrated approach to black root rot management. Several control methods used together have the potential to hold black root rot at low levels, these include: l  Dynasty CompleteTM seed dressing l  farm hygiene to stop further spread l  growing biofumigation crops l  avoiding rotation with crops that are hosts for the pathogen l  cultural methods such as delayed planting of fields l  good layouts to avoid waterlogged areas. CottonInfo received funding for this investigation and microbiology testing from the Cotton Research Development Corporation. Further reading Disease management CottonInfo — Information for growers Black root rot fact sheet CottonInfo — The IDN fast fact series October 2016 Black root rot and slow early season growth of cotton CRDC, David Nehl, Final report, Project DAN 122C