Wild parsnip

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Scientific name Pastinaca sativa

// Problem

Wild parsnip is a poisonous invasive weed that has invaded roadsides, power lines, pipelines and other non-crop lands. The plant is ubiquitous in some regions with plants found in any disturbed waste areas and in dense extensive stands. Wild parsnip causes a painful, blistering toxic reaction only when exposed skin gets sunlight on it. Due to its dense stands of plants growing up to 200 cm, people walking through wild parsnip can get exposed to the plant toxins on their legs, arms and backs. Its presence creates problems for workers, recreation and the general public.

// What to look for

Wild parsnip grows as a biennial or short-lived perennial that dies once it flowers. It has a deep, thick tap root that can growth up to 1.5 m deep, allowing it to reach deep water. What is different than most biennials, is that the wild parsnip root and crown must reach a critical size before the plant will flower, which can take up to 5 years. As a result, stands of wild parsnip contain a mixture of seedlings, vegetative rosettes and flowering plants. Since the flowering plants die that season, control should focus on killing the rosettes and seedling plants and preventing further seed germination.

Eighty per cent of the wild parsnip seed germinates within the first year. After the second season, the germination rate of any remaining seed falls off dramatically. Good pre-emergent control for 2 to 3 years is necessary for long-term control of this problem weed.

It is important to be able to identify wild parsnip, particularly seedlings and rosettes. Seedlings have long, narrow cotyledons and a round, round-toothed first true leaf. Rosette leaves are compound with up to 15 leaflets, some which may divide again to form leaflets. The leaflets are elliptic or elongated with toothed margins, some appearing to be mitten-shaped. In flowering plants, the erect stems are hollow between the nodes and grooved and slightly hairy. The leaf petioles clasp the stems. Stem leaves grow progressively smaller until they form bracts around the flower clusters. The flower clusters are a tall, multi-branched compound umbel, with the florets having 5 small yellow petals. The whole plant has a strong parsnip odour.

// Bayer Solutions

Post-emergent solutions
Applying Navius VM or Truvist to small parsnip plants – preferably when they are 10 - 15cm tall – can improve control of established wild parsnip seedlings and rosettes. Navius VM and Truivist can be used in preventing emergence of new seedlings.

If parsnip plants are taller than 15cm, effective control requires complete spray coverage of the foliage. Use application equipment that gives the best coverage of all parsnip plants while minimizing spray drift. Remember, taller plants, railroad ties, guardrails and other obstacles can shield or shadow smaller plants and limit contact with shorter parsnip. Since dense stands have seedlings and rosettes among the flowering plants, it may take a few years to get total control.

Persistent application period
For long-term control of this problem weed, 2 to 3 years of successful annual control in spring and/or fall may be necessary. After control, establishment of competitive cover is important to prevent new infestations.

Cleaning equipment following a herbicide application to a site, after mowing, ditching or any other work on infested sites will help to prevent linear spread down rights-of-way. For cleaning protocols for contractors: http://www.ontarioinvasiveplants.ca/files/CleanEquipmentProtocol_Mar152013_D3_FINAL.pdf

After control, establishment of competitive cover is important to prevent new infestations.


// Resources

Bayer Solutions : Wild Parsnip PDF

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