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Rorippa sylvestris - Noxious, imported weed.
Creeping Fieldcrest - Are you getting more than you bargained for?
Known variously in Holland as "Keek", "Kiek", or "Kik", the noxious weed Rorippa sylvestris has been coming into the US in the roots of imported bulbs and plants. Known to have been introduced within the roots of Lilies, Daylilies, and Hosta, and to have spread throughout most of the US, Rorippa sylvestris is extremely difficult to eradicate.
If found in your garden:
This form of Rorippa is more widespread in the US than we first thought. A serious problem in Holland for many years, Dutch friends in the industry have reported to us that Rorippa sylvestris is now so widespread that it has been downgraded to a "nuisance" to reduce costly restrictions. In others words, it appears they have given up on eradication.
In discussing Rorippa with our local Federal Agricultural Inspector, it seems that their hands are tied. To control the influx of this weed into the US is not feasible, short of stopping all plant importation or imposing quarantines.
Check your garden now for its tiny cluster of yellow flowers. Roots of this plant are white in color and it does not make a taproot. Repeated spraying with restricted chemicals in ornamental nurseries has been reported as effective, but prevention is still the best cure.
Before planting any Lily bulbs, Daylilies, or other perennial produced outside the USA, check your purchase for fine, loose, thread like roots. A single three-centimeter piece of root can make as many as 2000 more creeping yellow field cress plants in a single year. Think you got a real bargain from the Internet Auction win from a non-inspected Internet nursery? Remember, if they aren't licensed, then they are not inspected by the United States Department of Agriculture. A business license is not a nursery license! That bargain can turn into a nightmare in short order. Before buying anything from web-only 'nurseries' proudly promoting their material, or worse yet, "plants from my garden", be safe by getting a guarantee in writing that your purchase will be free of Rorippa sylvestris. Then if you do receive more than you paid for, hope that they are still in business and have not closed up one Internet shop door to open under a new name.
How fast does Rorippa sylvestris spread?
The options for the daylily bought over the internet and now engulfed by Rorippa sylvestris? The home gardener's options were limited, she couldn't pull it; each broken root piece would grow into another equally smothering plant. Dig it out? After digging 3 to 4 feet around this plant to a depth of 18 to 24 inches, where do you deposit the root infested soil? Spray the area with herbicides? Everything toxic enough to kill Rorippa sylvestris will kill your other garden treasures as well. Her chosen solution (outside of moving to another home) was to spray, killing everything in her garden around it and starting over. And the Internet-only seller advertising "direct from my garden" that sent it to her? Gone and not to be found!
The links below have photos which should help you identify any plants in your garden.
Wild Lily bulbs making up the genus Lilium belong to the family Liliaceae comprising of approximately 200 genera made up of approximately 2,000 lily species. There are in the neighborhood of 110 to 120 Lilium species depending on whose classification you reference. For the full article, click Knowledge Base