Weed of Week – St John’s Wort

We’re into week six of our Weed of the Week campaign, continuing to share important information on our region’s priority weeds. This week we’re looking at St John’s Wort.

Snowy Monaro Regional Council encourages our community to get to know our region’s unwanted (priority) weeds. Knowing what to look for and how to help, we can work together to protect the environment, help our farmers and support our community.

The impact of weeds on natural vegetation can be devastating and is estimated to cost the NSW economy approximately $1.8 billion annually (NSW Department of Industry, 2018).

What is St John’s Wort?

St John’s Wort (Hypericum perforatum) is an exotic, perennial, woody weed with perforated leaves and yellow flowers. It grows to about 30 – 90cm tall. Wort spreads via seed as well as underground runners and is very difficult to manage.

Why is St John’s Wort a problem?

• In extreme cases it can be toxic to stock and can cause photosensitisation (resulting in sunburn), failure to thrive, abortion and even death if grazed extensively by susceptible stock.

• St John’s Wort is a priority weed in the Snowy Monaro Regional Council area due to its toxic potential and invasiveness. This weed can be found along the road corridor, on lands around towns, on ungrazed farmland and on many rural properties.

• St John’s Wort will also readily invade bushland – including native grassland, woodland and forested areas – competing with native vegetation and reducing biodiversity.

• St John’s Wort spreads quickly through paddocks and along tracks and trails. It invades both native vegetation and improved pasture.

• Seeds stick to fleece and fur and can reduce wool quality.

• Vehicles, equipment, livestock and native animals can all spread seeds.

What can you do?

• Learn to identify and effectively control St John’s Wort in its early stages of invasion.

• Search your property for new germinations or regrowth of St John’s Wort. Plants are more obvious from early December when they begin flowering. You can find new leaves emerging from October. If you find plants, control them prior to the flowers forming capsules as this will prevent seed set.

• Avoid the use of non-selective herbicides which will destroy beneficial vegetation surrounding St Johns Wort plants. Maintaining a strong, competitive pasture is essential to every weed control program.

• Like many weeds, a well-managed, intensive grazing program can provide very effective control of St Johns Wort. Carefully consider your standard of fencing and livestock susceptibility before embarking on this adventure.

• Biological controls, including Chrysolina beetles, Gall midge (Zeuxidiplosis giardi), Green aphid (Aphis chloris) and St John’s wort stunt mite (Aculus hyperici) can be effective in controlling St Johns Wort in some situations. Seek advice before employing biological controls.

• Dispose of any plants you remove manually on-site or in the designated Weeds bins at a Council Landfill. Do not dispose of plant waste in your local park or reserve.

• Download the free NSW WeedWise app for detailed information on how to identify and manage local priority weeds: https://www.dpi.nsw.gov.au/biosecurity/weeds

• Visit Council’s website to understand how we can help you with weed management: https://www.snowymonaro.nsw.gov.au/140/Biosecurity-and-Weeds

/Public Release. View in full here.