Now is the time to look out for St John's Wort

By Callen Thompson, Mixed Farm Advisor, Central West Local Land Services

St John’s wort is spreading in the region, particularly the Warrumbungle Shire. Landholders are urged to identify and control this invasive weed to reduce the impact on their land and the environment.

We have known of infested areas around Coolah, Merrygoen and east of Coonabarabran for some time, but in the last two years there has been a marked increase with wort spreading through farms, lifestyle blocks and bushland. St John’s wort is actively flowering, so now is a good time for land managers to identify and control wort on their properties. St John’s wort will quickly overtake pastures and natural areas, particularly in hilly and inaccessible areas. Once it takes hold it is very difficult to control.

St John’s wort is an upright woody weed with a bright yellow flower. Flowering occurs from late October through to January. Stems are green through the flowering period, but will turn brown in late summer or if moisture runs out. The stems become reddish brown in winter.

St John’s wort spreads easily with sticky seeds that can stick to machinery, livestock or pest animals. The seed can pass through the digestive system and will remain viable. Seed can also spread by water movement or by wind over short distances. The seed may remain viable for up to 12 years.

St John’s wort is poisonous to livestock. It contains a chemical called hypericin, which causes photosensitivity. Other symptoms include weight loss, stillbirths and in severe cases, death. Young stock are more susceptible, with suckling stock still effected through the milk of their mothers. St John’s wort will compete with pasture species and can also create a vegetable fault in wool.

St John’s wort is spreading in our area, so it is important for all land managers to know how to identify it. Land managers should take particular notice in spring as the yellow flowers are easy to spot, even with the tall grass this year. It is worth noting that plants that are less than a year old, will not flower, so you may have young plants present that are hard to spot.

Once you identify wort, it is important that you control it quickly and  prevent seed set. Unfortunately, physical removal is ineffective as new plants will grow from root fragments, in fact wort can be spread through cultivation. Isolated plants or patches of plants can be controlled by spot spraying with a registered herbicide. It is important that you identify the immature plants that may not be flowering and spray them as well. They are often close to the older flowering plants.

Larger areas can be sprayed with a boom spray. For spot spraying and boom spraying, it is best to use a selective herbicide product that will not kill grass species, allowing for competition and limiting bare ground. Because seed can last for so long, monitor sprayed areas and respray as needed.

Stopping spread onto your property, and within your property is very important. Ensure that any hay or seed you bring onto the property is weed free and make sure all machinery and vehicles are cleaned down before entry.

Avoid grazing areas of wort and then moving stock to wort free areas. If you must graze wort, quarantine stock for at least five weeks to prevent seed deposit from faeces, fleece or fur. Do not move machinery or vehicles through infested areas and make sure contractors, roo shooters and other visitors are aware of these areas.

St John’s wort is spreading in the Warrumbungle shire. It is important for all land holders to be vigilant, learn how to identify it and control it as soon as they see it. If you would like help identifying St John’s wort, please contact your local councils weeds officer or Callen at Local Land Services (0417 348 687).

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