Cotton disease under attack

A novel method to better manage black root rot in cotton will see NSW Department of Primary Industries’ scientists at the Australian Cotton Research Institute near Narrabri test the potential of onions and marigolds as biofumigation crops.

It is hoped that onion or marigold crops may reduce the survival of the fungus in the soil, reducing the risk for following cotton crops.

The new method is part of a three-pronged approach by NSW Department of Primary Industries to develop an improved disease management strategy aimed at reducing the economic impact of the early season disease.

With previous work showing a correlation between the incidence and severity of disease with certain soil properties, researchers will also focus on what physical, biological or chemical aspects of the soil may actually suppress or support black root rot.

In addition, the research will determine whether Bion®, a synthetic chemical applied to the seed, can be used to slow down the build-up of the pathogen in the soil from initially low levels. The application method and direct effect on the cotton plant is also being investigated.

Black root rot is caused by the soil borne fungus Thielaviopsis basicola, which has a wide host range and is responsible for economic losses in many agricultural and horticultural crops worldwide.

The fungus infects the roots of cotton plants at the seedling stage causing slow early season growth, particularly when climatic conditions are cool and moist.  This slow start results in delayed maturity of the cotton plant, with high yield losses possible.

Because the fungus reproduces prolifically on the roots, each successive cotton crop deposits large numbers of spores in the soil, increasing the incidence and severity of the disease as cotton cropping continues.

NSW DPI plant pathologist David Nehl has been actively involved in monitoring the spread of black root rot in cotton over the past 10 years and is also researching the effects of early planting dates on the severity of the disease in cotton to provide advice to growers on how to successfully avoid the disease.

In order to boost the research effort, Dr Susanna Driessen from Western Australia was recruited last year to tackle a new project which aims to better understand the suppressive nature of some soils against the disease.

Dr Driessen said the challenge would be to develop an improved disease management strategy for this intractable disease.

“Currently, there are no fungicides registered or effective against the pathogen, with farm hygiene the only way to slow the spread between farms and within field on individual farms,” she said.

“If the research shows that some soils can suppress the disease, then the aim is to evaluate whether these soil properties can be transferred to other conducive soils as a direct control measure.

“Alternatively, they may be used as a predication of disease potential, which would then enable growers to make informed disease management decisions based on their soil type.”

Funding for the new black root rot research at Narrabri has come from the Cotton Research and Development Corporation and forms part of a co-ordinated effort through the Cotton Catchment Communities CRC to reduce the impact of black root rot on cotton production.