Botanical name: Rosa rubiginosa
Family name: Rosaceae
Overview
Sweet brier.
Sweet brier (also spelt sweet briar in many places) was originally grown as an ornamental rose but is now a major scrub weed in the South Island, especially in Central Otago and inland Canterbury. It is also found in the North Island, though generally only as a roadside weed.
It grows in tussock grassland and poor pastures where stony ground and light rain (often only 400 mm per year) limit competing growth. Pasture competition prevents new plants from establishing, though established plants are very competitive.
Rabbit infestations have helped the spread of sweet brier by reducing pasture vigour. Cattle, possums and birds spread the seed by eating the fruits ("rose hips") produced around the seeds.
Distinguishing features
Sweet brier leaves and stem
Sweet brier looks very much like a scrambling miniature rose, because this is basically what it is. Flowers are smaller than most cultivated roses, and are pink. The woody stems have many spines, some straight and some pointing downwards. Flowering occurs in summer and the pink fruits are ripe by early winter.
Leaves are composed of leaflets in a similar way to blackberry, but leaflets are spread down a stem, rather than radiating out from a central point as in blackberry.
There are also other species from the Rosa genus other than Rosa rubiginosa that have escaped into the wild, due to the growth of so many ornamental species from this genus throughout the country, and most have similar leaf shapes and some are also called sweet brier.
Control
Sweet brier fruits.
Most scrub weeds can be prevented from establishing in pastures if the pastures are competitive and sweet brier is probably more susceptible to competition than some scrub species. However, sweet brier causes problems where it is difficult to get competitive growth from pastures. Once it is present, goats can bring it under control.
Herbicides that will control it are metsulfuron, glyphosate and a triclopyr + picloram mixture. However, the economics of doing this in central South Island pastures is one of the main issues to consider, especially if more sweet brier will establish soon after control due to the low vigour of pastures.
