AgPest » Creeping yellow cress

Wide spreading, straggling, rhizomatous perennial herb usually 20- 50 cm tall
Yellow flowers, with four petals, 4-6 mm across, appear in loose clusters at the top of the flower stem from December to February
Seed pods curved, 10-15 mm long, on stalks of similar length
Leaves hairless, deeply divided into 4 to 10 lobes. Smaller leaves with fewer lobes on flower stalk
Creeping rhizomes can result in dense mats of foliage that smother infested land or crops.

Marsh yellow cress or poniu (Rorippa palustris) is native to New Zealand, although there are also races of the same species that have been introduced from elsewhere. Flowers are paler, leaves less divided, and seed pods shorter and wider than those of creeping yellow cress. Marsh yellow cress is not as common but it is also found in wet places throughout the country.

Native to temperate Europe and southwest Asia
First recorded in New Zealand in 1952 but most likely was here much earlier and perhaps overlooked or confused with other species
Now common in places throughout the North and South Islands
A common garden weed, also found in market gardens, under tree crops and on cultivated land (especially headlands), as well as in damp pasture and river beds.

Creeping yellow cress can be a very persistent weed and is hard to eradicate because of its rhizomes
Spread is by means of rhizomes and rhizome fragments, as well as by seed
Some local populations do not produce seed because plants are self-incompatible
Plant may produce allelochemicals that inhibit the germination of other plant species
Can withstand prolonged submergence under water
Hybridises with other species of Rorippa
Rhizome fragments can be moved in plants bought from nurseries or elsewhere.

Impact on crops

Can form dense, tangled masses of stems and intertwining rhizomes floating in water or creeping over mud
Stems and rhizomes may be several metres long, and can root at several points
Especially a problem in nurseries, from which it can easily be spread with ornamental plants sold in containers.

Impact on pasture

The creeping rhizomes can create a thick mat of weed which completely smothers pasture.

Impact on the natural environment

A pioneer species, preferring to grow on bare soil or mud
A common weed of waterways, wetlands, swamps, lakes, ponds and other wetter habitats in temperate and sub-tropical regions.

Pastures should be kept dense in autumn to prevent creeping yellow cress from establishing. This can be done by selection of appropriate grass cultivars or by grazing management.

Creeping yellow cress is not affected by many common pre-emergence herbicides
Flumetsulam controls creeping yellow cress without adversely affecting clovers and grasses. It should be applied before flowering and repeat applications may be necessary in subsequent years
In other countries, triclopyr + dicamba have given effective control but this combination will kill many other plants except grasses
MCPA or 2,4-D will give at least temporary suppression
Glyphosate kills the top growth but regrowth takes place afterwards.

It is more important to prevent nurseries becoming infected with this weed as getting rid of it after it has invaded can be very difficult
Hand pulling of plants is likely to leave behind root or rhizome fragments that can later regrow
Cultivation probably spreads the weed rather than controlling it.

Popay I, Champion P, James TK 2010. An illustrated guide to common weeds of New Zealand. New Zealand Plant Protection Society, Christchurch, New Zealand. 416 p.