WATER PEPPER
Persicaria hydropiper
DESCRIPTION
Water pepper is a summer annual often found in NZ pastures, especially in wet locations.
It is similar in appearance to willow weed, and the two are often confused. In practical terms the confusion doesn’t matter much, because the treatments are much the same.
Water pepper is an erect species, reaching about 75cm high. The stems are normally reddish in colour.
The leaves are narrow and pointed, about 12cm x 2cm, and quite willow-like in appearance. The leaf edges are slightly wavy. Water pepper leaves are bright green and usually evenly coloured, whereas willow weed differs by having dark blotches on the upper surface of its otherwise similar leaves.
Flowers are most commonly light pink or sometimes white, at the end of short stalks that curve downward. Flowering occurs from November to June.
HABITAT
Water pepper prefers wet places, including stream margins, around canals and ditches, and in ill-drained pastures. Pasture locations that have been heavily pugged over winter will often encourage spring establishment of water pepper.
Distribution is NZ-wide and common in both North and South Islands.
LIVESTOCK
Stock avoid water pepper due to the strongly bitter taste of the foliage. There have been local reports of suspected poisoning of stock, and in some countries (Australia, USA) water pepper is considered to be toxic to livestock.
PASTURE MANAGEMENT
Minimising pugging where possible will help, as will improving the drainage of pasture low spots.
PHYSICAL CONTROL
The plant has shallow roots and is easy to pull by hand, but infestations in damp areas will often be fairly substantial and beyond reasonable hand-pulling potential.
HERBICIDES TO CONTROL WATER PEPPER WEED
Selective control in pasture is possible, but becomes more difficult as the water pepper plants get larger. Once the plants are mature, selective control is going to involve the acceptance of clover damage. Better to treat water pepper at the seedling stage, when it is susceptible to herbicides that aren’t damaging to clover.
In situations where selective control is not required, G-360 GLYPHOSATE, G-540 GLYPHOSATE or Granny Herbicide soluble granular glyphosate can be used effectively at all growth stages.
Spot Treatment Herbicides to Kill Small Infestations and Seedling Waterpepper weed
- WHACK – 2,4-D 800 – 50g/10L water by knapsack or handgun. Add SprayWetter – 10ml/10L water to boost penetration and reduce rain risk period.
- Ranger Herbicide – 1g/10L by knapsack or 5g/100L by handgun, plus SprayWetter – 10ml/10L water. This option is a little more effective than WHACK – 2,4-D 800 when the water pepper seedlings get larger, but there will probably be some clover damage.
Boom Spraying Weed Killers to Kill Waterpepper Seedlings
- WHACK – 2,4-D 800 – 1.98-2.97kg/Ha in 300L water, plus 300ml SprayWetter .
- Rainbow & Brown MCPA750 – 2-3L/Ha applied to small seedlings only. Add SprayWetter – 100ml/100L water.
- Ranger Herbicide – 20g/Ha, plus SprayWetter – 100ml/100L water. Expect some temporary yellowing of pasture, and clover vigour may be checked for up to 3 months. Damage will be minimised, and often avoided, where pasture is growing well at spraying, and growth conditions remain ideal following application.
