Yellow flag iris: pretty, pushy invasive plant

Campbell River’s Most Unwanted, Part 3

An excessively pushy streak puts the invasive yellow flag iris in the top three on Campbell River’s most unwanted list.

“After bashing the blooming broom and tackling knotweeds, take a closer look at the aquatic yellow flag iris,” says Terri Martin, the City’s environmental specialist. “It’s true that such a pretty plant is a listed noxious weed under the Provincial Weed Control Act, which imposes a duty on all land owners to control this extremely pushy invasive plant.”

What’s the problem? They might be pretty, but…

Native to Europe, western Asia, and North Africa, yellow flag iris was introduced to Canada in the 19th century as an ornamental plant for ponds and water gardens. It has since spread to many waterways, including ditches, marshes, streams, shallow ponds and estuaries.

“In Campbell River, we’re particularly concerned about a very large infestation in the

estuary around Baikie Island,” Martin says. “Some of the plant communities that have been choked out by the iris are listed as rare or threatened and aren’t known to exist anywhere else in Campbell River.”

“Yellow flag iris creates a monoculture, replacing dozens of species of native plants. They outcompete native sedges that form the base of the estuary food web, reducing available nutrients and habitat for all species, including salmon,” says Sandra Milligan, Greenways Land Trust president. “Estuaries are the most productive ecosystems in our province, providing essential habitat needed for salmon to transition between fresh and salt water habitats, both as young smolts and as adults returning to spawn.”

This particularly persistent plant spreads by seeds and by underground stems or rhizomes, which transmit new shoots above the ground and roots below. The resulting mats of rhizomes can connect several hundred plants to produce a dense thicket that traps sediment, which effectively dry out the marsh.

“We don’t know the source of the infestation in the estuary but it is likely that seeds and plant fragments from an unknown source upstream drifted down and took hold,” Martin adds.

What’s been done so far?

Since 2012, the City has been tackling yellow flag iris on Baikie Island with help from the Nature Conservancy of Canada and Greenways Land Trust. The infestation was already well established and initial attempts to dig plants by hand proved inefficient. In 2013 and 2014, a small machine was brought in to assist removal efforts under the direction of a specialized contractor versed in invasive species control and restoration. To date, more than 20 tonnes of iris have been removed.

In 2017, the City funded approximately $2,500 for removal from Baikie Island City. Greenways Land Trust secured an additional $8,825 from the National Wetland Conservation Fund.

Led by Greenways Land Trust, efforts underway for 2018/2019 include removing regrowth from previously treated sites, digging out additional plants and experimenting with a soil covering to determine if shading is a viable option to deter these invaders. The general strategy is to remove small infestations in the outlying areas and then tackle denser infestations in the centre.

Progress has been made, but several more years of treatment will be necessary to meet the goal of near eradication.

New this year – Environmental Protection Bylaw amendments

Earlier this summer, the City adopted an amended Environmental Protection Bylaw to regulate defined invasive plants and noxious weeds by restricting planting and requiring removal.

“We are really pleased with the efforts by Greenways Land Trust and the many volunteers who work under their umbrella to gain control of the Baikie Island infestation,” says Councillor Marlene Wright, who holds the environmental portfolio. “The hope is that the community will help identify and remove any yellow flag iris upstream to prevent new infestations downstream.”

How to identify yellow flag iris

• The only “wet-footed” yellow iris

• The only iris in North America with entirely yellow flowers

• Blooms April to July

What to do about Yellow Flag Iris on private property

Quick removal of yellow flag iris when the patch is small and easier to dig by hand can help prevent it from spreading to other locations. For larger patches that are harder to dig all at once, be sure to at least clip seed heads off (look for these in July). Wear gloves to protect hands from toxic resin.

Grow native and regional plants instead

The most important part of invasive plant management is prevention. Native cattail and non-invasive iris species are among the options listed in the Grow Me Instead booklet from the Invasive Species Council of BC. This publication profiles 26 of the province’s most unwanted horticultural plans and offers many suitable alternatives for a range of growing zones.

Notes on disposal

Bag and take remnants of yellow flag iris to the Campbell River Waste Management Centre (landfill) for disposal at a reduced tipping fee ($65 per metric tonne). Because of their ability to spread, this species should not be placed in a backyard compost, curbside yard waste program or taken to the yard waste drop off centre on Willis Rd.

Please report yellow flag iris infestations to the City via email to terri.martin@campbellriver.ca.

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