Parsley Dropwort (Oenanthe pimpinelloides)
Parsley dropwort, often called carrot weed in New Zealand, is a deep-rooted perennial from the Apiaceae family. It’s most problematic in Northland, where it invades pastures and roadside areas, and is now spreading south through Auckland, Coromandel, and Waikato.
This weed is highly persistent due to its tuberous root system, which allows it to regrow after cutting or spraying. Stock generally avoid it because of its strong chemical compounds, particularly once it develops woody flower stems in late spring. In lawns and lifestyle blocks, the woody stumps left behind after mowing can be hard on bare feet and ruin the surface finish.
In pastures, parsley dropwort competes aggressively with grass, lowers feed quality, and taints hay made from infested paddocks.
Identification
Parsley dropwort has upright, branching stems that grow 30–70 cm tall and end in white umbrella-shaped flower clusters (umbels). The leaves are bright green and divided into rounded, irregularly lobed segments, giving them a slightly “parsley-like” look.
The key distinguishing feature is the presence of small, swollen tubers along its roots. These tubers store energy, allowing the plant to regrow after control attempts or during dry periods.
It can be confused with wild carrot (Daucus carota) and hemlock (Conium maculatum), but parsley dropwort leaves are broader and less finely divided. Wild carrot has very fine, feathery leaves, while hemlock leaves are deeply cut and fern-like.
Why It’s a Problem
Parsley dropwort is not readily eaten by livestock and becomes dominant where grazing pressure is uneven or soils stay moist. Its tuberous roots make it hard to eradicate, and it spreads easily through contaminated hay or machinery movement.
In lawns and turf, its coarse, woody flower stalks disrupt mowing and create hard stems that damage mower blades and leave the surface uneven.
Management and Prevention
Cultural control methods:
- Avoid spreading infested hay or soil: Tubers and seed can easily move to new areas.
- Mow early: Cutting before flowering can limit seed production, but regrowth will still occur from tubers.
- Improve drainage and soil health: Parsley dropwort prefers moist, compacted soils.
- Re-sow and thicken turf or pasture: Dense growth reduces the bare soil areas where parsley dropwort establishes.
Chemical Control
Parsley dropwort can be difficult to control due to its underground tubers, but trials in Northland have shown several effective options.
Most effective control options:
- 2,4-D ester (Pasture-Kleen, 3 L/ha) applied in winter or early spring (June–August) before flowering.
- MCPA offers similar control and can be useful where buttercups are also present.
- Clopyralid (NZLA BWC) at high rates gives good suppression and is suitable for spot-spraying in lawns or turf.
- Glyphosate and metsulfuron are effective in waste areas or for total vegetation control.
- 2,4-D/dicamba mixtures can also be used for spot treatment on scattered plants.
Once the plant begins flowering, control success drops significantly. Wiper applications with glyphosate or metsulfuron may help where the weed stands taller than surrounding grass, though care should be taken to avoid damaging desirable species.