Parks, Recreation and culture spring 2010

Invasive Alien Alert Milk , Milk thistle (Silybum marianum) is an What Harm Does the Do? How To Remove and Dispose? invasive plant from that When not controlled, Milk thistle can • For small areas with few , pull or from April to October. This noxious invader produce ten tonnes of foliage per hectare, dig up rosettes and plants which have chokes out native species, depriving them pushing out native and rare plants in begun to grow upright stems, before of light and room to grow. Its large, woody sensitive areas. Milk thistle can also cause seed heads form. Use a shovel to cut thorns can pierce shoes and can be toxic nitrate poisoning in animals such as cattle the plant off about 2.5 centimetres to animals that eat its . and sheep. below the ground so the plant will not A single Milk thistle blossom can produce re-sprout. Chopping the leaves from one thousands of seeds from May to July, so a Where Is It Located? side of a rosette can provide access to single seed can start a new invasion. City Milk thistle has a limited distribution in the central growing point. Greater Victoria. In Victoria, the area around Parks staff are removing Milk thistle from • CAUTION: Wear protective clothing to Haegert Park is the only site where Milk public lands and are asking residents to avoid puncture wounds from the spines. thistle has been spotted. The plant may help remove this nasty alien invader should To be fully effective, all mature seed have been imported to the area as a garden they see it in their garden. heads need to be bagged and removed plant or part of a seed contaminant. so no new seeds remain. Immature What It Looks Like A new invader to British Columbia, Milk seeds can still continue to develop Milk thistle is a robust, branching winter thistle grows in both sun and shade, in cut plants, and the less stem that annual/biennial plant that reaches up to and in moist and dry locations. Plants remains attached to the head, two metres in height. It produces one germinate well in roadsides, ditches and the faster the seed head will dry out. large, pink-purple flower per stem and newly disturbed garden beds. They can • Place plants in sealed garbage bags, has spines along the stems and also quickly spread to natural areas such as the seeds can ripen even after they edges. Heavy spines surround the flower as Garry Oak meadows. have been pulled. head (see above photos). Milk thistle has distinctive white marbling patterns on shiny What You Can Do • Label garbage bags as ‘Milk Thistle.’ green leaves. If you see Milk thistle on public lands, • Drop off marked bags at the City’s One plant can produce over 6,000 seeds please report it to City Parks staff to Public Works Yard at 417 Garbally Road, in just one year. It can also overwinter prevent this invader from spreading. on Saturdays from 7 a.m. – 2 p.m., free as a rosette of green leaves close to the You can also help by checking for this of charge. Proof of residency is required ground. While the plant flowers, its seeds noxious weed on your property and in the form of a valid driver’s licence. fall nearby and are spread by erosion, removing it. animals, rain and human activity. Fall rains help germinate the seeds, however, seeds When To Remove It? can lie dormant in the soil for at least The time to remove Milk thistle is in April and nine years. early May, before the plant goes to seed.

To report Milk thistle (Silybum marianum) in Victoria, please contact: City of Victoria, Parks Division T 250.361.0600 E [email protected]

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