It's the season to report pest plants

During the summer and early autumn, it becomes a lot easier to identify pest plants that can lay incognito for much of the year.

From December through to April, many pest plants produce distinctive flowers or seeds making them easier for the public to identify. Our biosecurity officers need your help to report these pests and stop the spread of these highly invasive species.

Moth Plant (Araujia hortorum)

Moth plant was found recently in a back garden in the Belfast suburb of Christchurch. While it does have pretty pink and white flowers, moth plant can rapidly grow into dense infestations smothering other plants. Its nickname is cruel plant as it clogs up the fragile mouth parts of butterflies, leading to starvation.  

Now is the time to check your back garden, the pods are easy to identify:  

• Its seed pods are very distinctive, pear-shaped, thick and leathery containing many black thistle-down seeds.
• Its bell-shaped flowers are white with occasional pale pink streaks. 
• Its leaves are dark green, hairless and dull with a grey downy underside.

Do not confuse moth plant with the edible vegetable – choko. The pods may look similar, but moth plant is not edible, the sap is poisonous and can cause skin irritation.  

Purple loosestrife (Lythrum salicaria)

Purple loosestrife has been located recently in Centennial Park in Timaru. This declared pest thrives in damp ground or shallow water and very quickly forms tall, dense infestations preventing any other plant species to grow. Purple loosestrife can spread quickly as a single mature plant can produce over two million ground pepper sized seeds each year.  

Purple loosestrife is easy to spot now by its large, flower spikes covered in purple flowers:

• It grows between 1-2 metres tall.
• Its stems are woody and pink at the base.
• Its leaves are narrow sometimes covered in fine hairs. 

Knotweed (Fallopia/Reynoutria spp.)

A new site of knotweed has been found in Governors Bay after a report by a keen-eyed public member. There are only two other known knotweed sites in Waitaha/Canterbury, help us keep it that way by reporting any potential sightings.

Knotweed grows very quickly, and its tough shoots and roots can break through hard structures like gravel, tarmac, and concrete causing, damage to foundations, paving and roads, and flood prevention structures. It has even caused significant damage to properties overseas and has impacted house values and sales and insurance claims. It has the potential to impact significantly on our waterways by impeding water flow, narrowing channels, and impacting recreational values.

Asiatic knotweed

• 2-3 metres tall.  
• Leaves are triangular with pointed tips, up to 15cm long.  
• Zig-zagging stems are hairless and reddish/purple when young and fade to green when mature. They become hollow with purple speckles.  
• Small off-white flowers appear on dense flower heads between December – March.

Giant knotweed

• Up to 4 metres tall.
• Leaves are heart-shaped and very large, up to 40cm long and 22cm wide, sometimes covered in fine hairs underneath.
• Stems are thick, hollow and often green to reddish-brown.  
• Flowers appear between November – April. No seed is produced.

Bohemian knotweed (Asiatic x giant hybrid)  

• 2.5 – 4 metres tall.  
• Leaves can either be shovel or heart-shaped shaped, both shapes can appear on a single plant.

Great willowherb (Epilobium hirsutum)

When you’re out and about exploring your local wetlands, lakes, and rivers, keep your eyes peeled for the invasive plant, which is a great willowherb. This pest is currently only found in Waitaha/Canterbury.

From December to April, great willowherb grows distinctive pink flowers with a white centre making it easier to identify:

• flower petals have a notch on the edge and are 2–3 cm in diameter
• leaves are slightly hairy with a ragged edge attached directly to the stem.
• An aggressive invader, great willowherb can reach up to 2m tall and can rapidly form dense infestations that outcompete native species. 

A big thank you to everyone who has taken the time to report potential pest sightings to our biosecurity team. With the help of the community reporting, we have been alerted to some highly invasive pest plants at new sites and been able to quickly control them to prevent further spread.

If you think you have found any of these pest plants, don’t attempt to remove them. Instead, take a picture, record the location and report any sightings via our online form or call us on 0800 324 636.