What does it look like?
Periwinkle is a scrambling groundcover plant that resembles a vine. The trailing stems can grow more than 2m long and take root where they come in contact with the soil. Its leaves are glossy, 4-10cm long, 3-7cm wide and arranged in opposite pairs on the stem. It produces 5-petalled blue-violet flowers of 4-5cm diameter.
Periwinkle is a widespread escapee from cultivation. It grows best in moist, shady places like waste places, riverbanks, roadsides, forest margins and shrublands.
Why is it a problem?
This species is fast-growing, tolerant of shade, and moderately tolerant of dry or wet conditions. Its creeping and layering habit allows it to form dense, long-lived stands. It can regrow after being damaged or grazed and will dominate bare areas and outcompete native ground-cover species.
Periwinkle does not usually produce seeds but can regrow from fragments of roots and stems.
Control methods
Physical control
Dig out very small plants. Dispose of plant material at a refuse transfer station or burn. Ensure you check for regrowth. Or
Smothering: Use black plastic or weedmat. Cover sites as they are, or rake into big rolls and cover (6+ months). Hand-remove surviving plants. Or,
Mowing: For level, easily accessed land, mow with a lawnmower on a very low setting, 2-3 times a year. As it regrows, follow up by grubbing remaining roots with grubber or shovel. Dry thoroughly then leave on site to rot down. Periwinkle 1-2 years to eradicate.
Herbicide control
Weed wipe (all year round) using 500ml glyphosate + penetrant per 1L water. Or
Spray (all year round) using 200ml glyphosate (360g/l) + 1g metsulfuron-methyl (600g/kg) per 10L. Avoid use within drip line of susceptible species. Requires constant follow up. Apply twice a year in spring and autumn. Treatment is required for three or more years.
CAUTION: When using any herbicide or pesticide, PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and safety requirements are followed.
Related links
http://www.nzpcn.org.nz/flora_details.aspx?ID=2637
http://www.nzflora.info/factsheet/Taxon/Vinca-major.html
https://www.weedbusters.org.nz/what-are-weeds/weed-list/periwinkle
