The place of bio- control agents

The only exception to this has been the parasitoid introduced to control clover root weevil; this began working well within a couple of years.

“But in most cases biological control is slow. Farmers are reasonably impatient people and they like to see things happen tomorrow. We have to accept that most biological control is slow, but the beauty is once it’s there it’s free and it will do its thing for a long time.”

Biological control suits sheep and beef hill country farms, Fraser says. It’s too difficult to use a tractor and too expensive for a helicopter so there is a definite need for biological control. 

While chemical sprays are an option, most farmers would prefer the other options.    

“The other thing about biological control is that you won’t eradicate the pest or the weed. The word is control, Fraser told Rural News. “You have to have the weed (or other pest) there as the host for the bio-control agent to live on. If you got rid of all the cali thistle then the beetle would die as well.”

Fraser says many pests in New Zealand have natural predators in their countries of origin that could be exploited as bio-control agents. 

“A lot of the weeds and pests that have come into New Zealand have done well because they have escaped from their natural predators.” Biological control aims at reuniting the pest with its natural enemies.