Radicula sylvestris; Keek; Yellow fieldcress

Stems - Herbaceous, erect, from rhizomes, glabrous, green or becoming purple in the strong sun, ribbed, to +/-35cm tall, branching (Missouri Flora Web).

Leaves - Alternate, petiolate, deeply pinnatifid. Basal leaves to -10cm long, 2-2.5cm broad, with +/-6 main divisions per side. Cauline leaves similar but reduced. All leaves glabrous or with very few short hairs. Divisions of the leaves toothed. Upper leaves with thinner and fewer divisions than the lower. Tissue connecting the divisions of the leaves 0.2-0.3mm broad (Missouri Flora Web).

Inflorescence - Terminal and axillary racemes to +10cm long. Axis glabrous. Pedicels to 4mm long in flower, expanding to +/-1cm long in fruit, glabrous. Inflorescence compact in flower, quickly expanding. Siliques to 1cm long, 1mm in diameter, cylindric but slightly compressed, glabrous, with a beak to 1mm long (Missouri Flora Web).

Flowers - Petals 4, distinct, spatulate, yellow, glabrous, to +4mm long, 1.5mm broad, rounded at the apex. Stamens 6, erect, 4 larger and 2 smaller. Filaments yellow, glabrous, to 3mm long. Anthers yellow, 1mm long. Ovary cylindric, green-yellow, glabrous, 2mm long in flower, superior. Style .5mm long. Stigmas globose-capitate, .7mm broad. Sepals 4, distinct, yellow, erect to spreading, cupped, mostly glabrous but often with a few hairs at the apex externally, entire, 2-2.5mm long, to 1mm broad, subulate (Missouri Flora Web).

It is conservatively estimated that more than half of the 81 ecoregions have been invaded by R. sylvestris in the United States. Notable exceptions include Texas, Oklahoma, Florida, Georgia, South Carolina, Nevada, South Dakota, and Wyoming, although this may reflect inadequate sampling effort (USDA, 2008).

The first Great Lakes sighting occurred in 1884 near Lake Ontario.

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental	Socioeconomic

There is little or no evidence to support that Rorippa sylvestris has significant socioeconomic impacts in the Great Lakes.
Rorippa sylvestris is designated as a noxious weed and is considered a serious pest to horticulture (ornamentals) and potential threat to crop and grazing lands. It can reduce bulb crop value and marketability as a contaminate of nursery stock.

There is little or no evidence to support that Rorippa sylvestris has significant beneficial impacts in the Great Lakes.

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Control
Once established, this plant is very difficult to control.

Physical
Readily re-grows from rhizome fragments – most attempts at physical control only exacerbate the problem when small fragments are missed and regrow.

Chemical
Pre-emergent herbicides suppress top growth but do not kill rhizomes which quickly produce new plantlets in response to the loss of the top. Glyphosate is marginally effective.  Selective post-emergent herbicides are not available. (NC State 2012)

Preemergence control was excellent with dichlobenil granules at 3 or 6 lb/A, isozaben at 1 or 2 lb/A and a geotextile/herbicide (17.5% Trifluralin). The geotextile fitted as collars alone were not effective. Trifluralin incorporated into the surface 2 inches at 2 lb/A was effective but did allow some emergence. Trifluralin plus isoxaben or oryzalin plus isoxaben were also effective at rates of 2 plus 0.5, 4 plus 1, or 6 plus 1.5 lb/A, or 3 plus 1, 4.5 plus 1.5, or 6 plus 2 lb/A, respectively, of the two herbicide combinations. Metolachlor at 3, 4.5, or 6 lb/A was ineffective for preemergence control of 3 cm rhizome pieces. Post emergence control was not commercial with 2,4-D, triclopyr, clopyralid or a combination of the latter two, when treated in the 6 to 8 leaf stage with 0.25% or 0.5% solutions. (Elmore et al 1996)

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.