6 July 2001


THE search for natural methods of controlling pests and diseases in crops is expanding and one of the exhibits planned for the Scottish Agricultural Colleges section of the Science Into Practice area was growing brassica plants to combat soil-borne disease organisms.

Research into the use of brassica plants for combating pests and disease organisms in the soil is well established in Australia, where some types of brassicas have been bred specifically for their bio-fumigation characteristics. The research project at the SAC Aberdeen is evaluating the effects under Scottish conditions. This year, a research team led by Elaine Booth is assessing the level of control the brassica treatment can achieve against rhizoctonia, the cause of black scurf in potatoes.

Brassica plants contain a group of chemicals called glucosinolates, and these have a toxic effect on some soil-borne organisms including some types of fungi and other pathogens.

Brassicas can be grown and harvested so the glucosinolates can be extracted and applied to the soil as a natural chemical treatment. But an easier – and possibly more effective – alternative is to grow the brassicas in the field where treatment is required, and then cultivate the plants into the soil where the chemical is released gradually as the plant tissue breaks down.

This is the approach Dr Booth and her colleagues are evaluating. For this years trials four different brassica species, all known to contain different types of glucosinolate, were planted as a catch crop in a field where rhizoctonia is known to be active. When the brassica plants were about 50cm (20in) high they were ploughed into the soil, which was later planted with potatoes.

Potato foliage

During the season the potato foliage is being examined for evidence of rhizoctonia infection, and after harvest the tubers will be checked for black scurf.

"Some types of brassica were traditionally grown for ploughing-in as a green manure crop, and farmers and gardeners were aware that this was beneficial for the following crop," says Dr Booth. "It is possible that some of the benefits they observed were due to the bio-fumigation effects of the glucosinolates from the brassicas.

"Glucosinolates have the potential for dealing with a wide range of pathogens in the soil including slugs and leatherjackets as well as micro-organisms. The research is at a very early stage and we still have a great deal to learn about the effectiveness of different types of brassicas and the organisms they help to control, but it is an interesting approach to crop protection and it could have considerable long term importance," she says.

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