Giant hogweed is one big and scary weed

Noxious weeds: Giant hogweed can reach heights of six metres

It’s not often a weed grabs the attention of both urban and rural landowners across the province, yet in 2015, giant hogweed was a weed everyone had an eye out for.

As we wrap up the growing season in 2017, this prohibited noxious short-lived perennial is still on folks’ minds and is often mistaken for the very common native plant, cow parsnip.

Concerns were raised because giant hogweed can cause painful burns and/or blistering, and even hospitalization in some cases. Luckily cow parsnip — giant hogweed’s significantly less harsh cousin — is much more prevalent in Alberta.

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So how do you tell the difference?

It can be tricky and there are many similarities, but size is a good way to tell them apart. Giant hogweed can reach a height of 20 feet and have a stalk diameter of one to three inches while cow parsnip generally is five to eight feet high and has a stalk diameter of one to two inches.

Stems also differ in that giant hogweed has purple spots and stiff bristles, compared to cow parsnip’s few purple areas, deep ridges, and fuzzy hairs.

Flower clusters are very similar and both plants have lobed leaves (although giant hogweed can have a leaf span of about five feet).

Prevention is the best way to inhibit weed spread. Once established, control is best done in the spring when the plants are small, although residual herbicides applied in the fall may help. Clipping flowers will reduce the spread of seed. Since the weed requires soil disturbance to spread, cultivation is only productive when all or most of the plant root has been removed. Annual removal may be necessary.

For more information on this or any invasive plant, contact your local agricultural fieldman or the Alberta Invasive Species Council. This is the final instalment of the series for 2017. Look for more articles next spring.

Aimee Delaney is a conservation assistant for Red Deer County.

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