Farm hygiene important in pest management

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David Murray, Toowoomba
Farm hygiene is an important component of integrated pest management (IPM), particularly when it comes to managing pests such as cotton aphids and Cotton Bunchy Top (CBT) disease.



Recent surveys of cotton-growing areas indicate the presence of aphids and CBT, and wetter conditions through the coming winter could favour the growth of weeds that are hosts for aphids and also increase survival of cotton volunteers that carry CBT to the next season.

The photo (right) shows volunteer cotton with CBT symptoms adjacent to the current season cotton crop (Photo: Lewis Wilson, CSIRO)

CSIRO and Cotton CRC entomologist Dr Lewis Wilson suggests that growers maintain good farm hygiene to reduce the risk of aphid or CBT problems next season.

CBT can stunt the growth of cotton plants and, if plants are infected when young, dramatically reduce yield.

CBT is spread by cotton aphids when they feed. Both cotton aphids and the disease need a host plant for survival through winter.

Cotton is a good host and volunteer or ratoon cotton plants can be found on farms all year. These plants can carry the disease and aphids through winter. Aphids can then move to cotton crops in the following spring and infect plants with the disease.

Photo: Fallow field with a high number of volunteer cotton plants, a potential resevoir for cotton aphid and CBT (Lewis Wilson, CSIRO).

While it is likely that CBT will survive on alternative weed hosts, these relationships have not been studied.

In recent field inspections on the Darling Downs, cotton volunteers were found on virtually every farm.

Many of these volunteers showed clear symptoms of CBT, such as angular leaf mottling and small leaves (see photo below, Photo: Lewis Wilson, CSIRO).

Cotton CRC extension officer Rod Gordon said that regular rainfall through the summer had encouraged growth of cotton volunteers, many of which were glyphosate-tolerant and difficult to control with herbicides. Wet fields have also limited opportunities to control volunteer cotton, with some fallow fields and field margins containing quite high densities.

The importance of controlling volunteer cotton in fallows can not be stressed enough. Minimising host availability is critical to ensure that we do not see a repeat of the 1998 CBT outbreak.

More information on cotton aphid and CBT can be found on the Inside cotton website (search for CBT).