Giant rhubarb

Giant rhubarb is a rhubarb-like herb reaching more than 4m wide. It competes with native vegetation and prevents seedling establishment.

Description

• Leaves are very large (up to 2.5m high and 4m wide), prickly and dull green.
• Leaves die back to large, creeping stems over winter.
• Flowers are minute, green or pink/red and on large flower spikes up to 1m tall
• Fruits are small and orange.
• Dispersal via seed. Vegetative spread from rhizome fragments.
• Habitats include riparian margins, wetlands, coastal areas, and cliffs.

Giant rhubarb is a hybrid species, a cross between Gunnera tinctoria (Chilean rhubarb) and Gunnera Manicata. Giant rhubarb looks similar to Chilean rhubarb, however, it has a dull green leaf surface where as Chilean rhubarb leaves are shiny. Giant rhubarb also grows larger and has longer, narrower flower spikes.

What you need to know

It grows into large plants with very big leaves, forming dense patches that can shade out and suppress native vegetation and exclude virtually all other plants.

Management approach

Community-led

These organisms have not been legally declared as pests but may be of interest to the public as they occur regularly in the environment. They may be capable of causing adverse effects to the values of Waitaha/Canterbury.

Consider removing both these invasive species from your property and consult your local council for appropriate disposal. Consider lower-risk alternatives for your garden, such as native plants.

Control

Physical control

• Small plants can be dug out, taking care to remove all of the rhizome to prevent re-infestation.
• Plant parts requiring disposal: Seeds and rhizomes.
• Contact your local council for appropriate disposal locations.

Chemical control

• No qualifications: Cut the leaves and flower stalks at the rhizome and paste with herbicide gel containing glyphosate or picloram.
• Certified handler/experienced agrichemical user: Foliar spray with 20ml glyphosate plus 2ml penetrant per 1L of water.
  For best results, apply herbicide in spring when Chilean rhubarb is actively growing.

Caution: When using any herbicide or pesticide please read the label thoroughly to ensure that all instructions and safety requirements are followed.

Biological control

• Biological control is currently not available for this species.