Turning the enemy

A new generation of environmentally friendly weapons against weeds and insect pests: seen here, Ricardo Segura recruiting potential bio-control agents on the Oronoke Flood Plain, Venezuela.

SCIENTISTS in the US are looking at some of our most damaging plant diseases to see if they can be turned into biological control agents. Gavin Ash from the Charles Sturt University attended a NATO-backed seminar in Venice this year where scientists from all over the world pooled their work on bio-control.

"In the US they're talking about modifying organisms like Sclerotinia, a fungus which attacks a wide range of plants, including crop plants, so that it would attack only weeds," says Dr Ash. "We know there is an exchange of signals between some fungi and their host plants which is triggered by the release of enzymes. If we could change the way those enzymes are expressed, then we could match the fungus and the host more precisely."

Dr Ash also cited the example of bees being used to carry biological control agents into the flowers of crops such as raspberries and strawberries, as a means of controlling botrytis, as an example of the innovative work being done with bio-pesticides.

"There's no doubt we're about to go into a new phase in the development of bio-herbicides and bio-pesticides," he says. "In the past the emphasis has been on finding naturally occurring control agents and adapting them to meet our requirements. The new move will involve genetic modification of naturally occurring control agents, something that, in the current climate, will need to be carefully handled."

Change the way we think

Dr Ash warns that if we're to make the best use of bio-herbicides and biopesticides, we' ll need to change our expectations. Unlike chemical control agents they won't completely eliminate a weed or a pest, instead they'll reduce its impact to a point where it is no longer commercially threatening.

"My team is working to find bio-herbicides that will control ryegrass and star fruit, a serious weed in rice," said Dr Ash. "We're close to a release of a star fruit agent which reduces the vigour of the weed so that it can no longer compete with the crop or set seed."

Dr Ash's work with ryegrass has the backing of growers and the Federal Government through the GRDC and he says that research into bio-agents will always probably rely on the backing of similar agencies. "Multinational chemical companies don't have the expertise to work in the field. They concentrate their efforts on 'one-size-fits-all' chemicals for high-volume markets," he says.

"We're never going to develop a bio-herbicide effective against all grass weeds for example. But at Charles Sturt we've found that we can mix bio-herbicides with as little as one-sixteenth of the recommended amount of a chemical and still get good control."

While Dr Ash doesn't believe that the biological control industry should face the same stringent certification tests as the chemical industry, he does believe that some form of licensing arrangement is overdue. "The very high costs associated with the certification of chemical controls have forced companies to concentrate on high-volume crops. We shouldn't force the biological control agents down that path but some sort of quality assurance programs to certify safety and effectiveness are needed."

Contact: Dr Gavin Ash 02 6933 2765