Solanum mauritianum
This months ‘Weed of the Month” is the ugly, itchy invader woolly nightshade, sometimes known as tobacco weed. It made our Dirty Dozen list because it is spreading rapidly around the Whangarei Heads peninsula, and left to its own devices, over time it will take over the road edges, shrublands, forest margins, forest gaps, forestry and coastal areas. Both visually and ecologically it is not something we want out at the heads. It is also easy to identify and control, so we can make a difference if the community works together to tackle it.
What does it look like?
A kerosene/capsicum-smelling shrub or small tree, growing up to 10m tall, with whitish, branching soft-woody stems. All parts covered in dense felt-like hairs. The large velvety, oval leaves (10-35 x 3-15 cm), are grey-green on the upper surface, and white to yellowish underneath with prominent ‘ears’ (25mm) at base which clasp the stem. Produces dense clusters of mauve to purple flowers (15-20 mm diameter) with yellow anthers, followed by clusters of round berries (1 cm diameter) that ripen from hard green to soft, dull yellow and whitish, branching, soft-woody stems.
Why is it a problem?
Forms dense, often pure stands, crowding out other plants, and inhibiting or preventing the establishment of native plant seedlings (it is allelopathic – meaning they produce toxins that poison the soil).
It grows and matures rapidly, producing many well-dispersed seeds most of year. Berries are toxic and the hairs/dust from the plant irritates skin, eyes, nose, throat. It tolerates wet to dry conditions, salt, all well-drained soils, hot to cool temperatures, semi-shade, damage and grazing.
It will invade heavily disturbed forest and light gaps, shrublands, coastal and estuarine margins, and wetlands.
How much of it do we have on the Whangarei Heads Peninsula?
This weed is spreading fast. Long time residents know there was none here at all until the 1980s, when seeds came in on machinery at Manganese point, and from there it has now spread all over the Heads, and its rate of increase is increasingly rapid (weed invasion starts slow and then becomes exponential). However, it is still not YET a dominant species in most of our natural areas, and by taking action stopping the spread we can make a huge difference.
How does it spread?
Birds, especially native pigeon, eat the large fruits and spread the seeds. It often grows and spreads along roadsides and disturbed areas.
What can we DO about it?
Lots! Woolly nightshade grows and matures to produce large amounts of seed very quickly, but it quite easy to kill. By tackling the outlying individuals we can greatly reduce the rate of spread and the amount of seed entering the local environment. Keeping forests healthy and intact also reduces the spread as woolly nightshade invades more open and disturbed habitats. There is also a biocontrol agent in development.
How do I control it?
- Pull up all small plants, dig out large ones ensuring no remaining roots are exposed to light as these will regrow.
- Cut & stump application: Cut tree down and treat stump within 10 minutes with (200ml Tordon Brushkiller/1L water) or (100ml triclopyr/1L water ) or Picloram gel). Undiluted glyphosate can also be used but extra care must be taken when using undiluted herbicide.
- Frill and fill: make deep cuts (8cm wide, 2cm deep) into the sapwood at regular intervals around the base of the tree, taking care not to ring-bark the plant. Immediately saturate the cuts with (200ml Tordon Brushkiller/1L water), or Picloram gel). Wait until the liquid subsides/absorbs and then apply again. Undiluted glyphosate can also be used but extra care must be taken when using undiluted herbicide.
- Drill & fill: Drill (c.12mm drill bit) sloping holes into the sapwood at 20cm intervals around trunk, & immediately fill each hole with (200ml Brushkiller /1L water), or with 10-15mls of undiluted glyphosate (extra care must be taken when using undiluted herbicide.
Spray: (25ml Tordon Brushkiller /10L water), or (60ml triclopyr +10ml penetrant/10L water).
Does not tolerate shade well. Maintain shade by planting dense cover, protecting habitat integrity. Kill standing where possible to allow easy access for seedling follow up. Follow up for 3 years. Maintain rolling front of control.
CAUTION: when using any herbicide or pesticide PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and safety requirements are followed.
Click here for more information on the herbicides referenced in the control methods
