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Published: 2002-12-11 00:00:00

Environment Waikato wants farmers and landowners to get tough on ragwort and thistles this summer.

The Council’s Plant Pest Officers are mounting a concerted effort for the next six months to help control the weeds.

Ragwort is widespread throughout the Waikato and can be spread by livestock and in contaminated hay. It is a biennial herb growing up to a metre tall, which reduces the productivity of land and is particularly toxic to cattle and horses. It may also taint milk and honey. Each plant can produce more than 50,000 seeds that remain viable for at least eight years, and it can reproduce from crowns, roots and seeds.

It is also common on waste land, river beds, swamps and open forests, quickly dominating pasture and excluding other plants.

Under Environment Waikato’s Regional Pest Management Strategy, ragwort has two control standards for different parts of the Region, depending on how prevalent it is. The aim is to prevent its spread into un-infested pasture, and reduce and contain infestations.

In the Hauraki, Thames Coromandel, Waipa, parts of Franklin, Waikato, Matamata, Piako, South Waikato and Otorohanga and Hamilton city areas it is a “total control” plant pest, meaning all plants must be removed and prevented from flowering.

A biological control programme is also operating using the ragwort flea beetle at a number of Waikato sites.

Nodding and plumeless thistles are aggressive pasture species which reduce the carrying capacity of land and obstruct and injure stock. They are found on roadsides, waste land in crops, hill country and grasslands widespread throughout the Waikato.

They are total control plants in Thames Coromandel, Matamata Piako, South Waikato, Waipa, Hamilton City and Hauraki districts and in parts of the Waikato, Franklin and Otorohanga districts. In other areas they are boundary control pests which must be cleared for 50 metres from boundaries.

Grubbing is effective for removing scattered plants, or seedlings and small plants can be controlled with boom spraying in autumn to early winter.

Three biological control agents have been released in the Waikato to feed on thistles – the Receptacle Weevil, Crown Weevil and Gall Fly.