Ragwort bio-control agents working well in Manawatu

Annual property inspections in the Manawatu have produced positive results for ragwort bio-control agents.

Ragwort senecio jacobaeae is a hardy plant with conspicuous yellow flowers, has the ability to compete with pasture species and contains alkaloids that are toxic to stock.

Horizons Regional Council environmental management officer Neil Gallagher, in a council media release, says three bio-control agents are at work in the region to reduce ragwort spreading between properties.

“Ragwort is capable of producing in excess of 50 000 seeds per plant and while sheep are capable of controlling small plants, its unpalatable to horses, deer and cattle,” he says.

“We have three bio-agents that attack ragwort; the cinnabar moth, ragwort flea beetle and ragwort plume moth. All three of these were present at a recent visit to two Manawatu dairy farms and the landowners considered the bio-control to be at a really good level.”

Kiwitea dairy farmer Wayne Bennett says the bio-agents took a few years to establish themselves but they have been really successful.

“Two years after buying our farm it was nearly completely covered in ragwort. Thanks to the combined efforts of the cinnabar moth, flea beetle and plume moth, ragwort is hardly there now,” says Mr Bennett.

“We’re extremely happy with how well bio-control has worked on our farm as we don’t like to use a lot of spraying to control weeds.”

Mr Gallagher says of particular interest this year is the abundance of cinnabar moth caterpillars.

“These caterpillars were originally imported from England in 1926 and then re-released in the 1980’s. The caterpillars damage ragwort by feeding on leaves and flowers, with the severity of the attack depending on the number of caterpillars as well as working in conjunction with the other two bio-agents,” he says.

“At the two dairy farms visited there were was an abundance of caterpillars and damage seen at both. It was obvious the combined effects of the bio-agents working together were keeping the ragwort at acceptable levels.”

Over the next few months Horizons pest plant staff will continue to monitor sites to assess how the agents are performing and move them to places where they are needed

For more information regarding bio-control agents Neil Gallagher can be contacted on free phone 0508 800 800.

Bio-control is a technique used worldwide to restore balance between a weed and the environment by recruiting some of its key natural enemies. Pest plants that have been introduced to New Zealand are often not considered a weed in their home country because there are bioagents there to control them. If it can be determined what these agents are then there is hope to restore the balance.

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