A New Invader

A new invader of aquatic and riparian wetland habitats has recently been discovered in southeastern Wisconsin. Vietnamese parsley (Oenanthe javanica, also known as Java water-dropwort or water celery) reproduces via seeds and runners (stolons), which may extend into waterways and break off, spreading fragments downstream that can establish new patches.

Vietnamese parsley is most easily detected and identified during its August and September flowering period, which is later than most, but not all, of its relatives in the carrot family. Identification is relatively difficult, because Vietnamese parsley is not yet included in regional floras and field guides.

Vietnamese parsley occurs in wet riparian areas, marshes, and areas of shallow, slow moving or still water in full sun to partial shade. It was first reported in Wisconsin as an escape from an artificial pond near Brodhead, where it had been planted as an ornamental. It is also widely used as a vegetable in Asian cuisine.

Invasions of Vietnamese parsley are capable of choking streams and displacing native riparian vegetation.   Wisconsin Species Assessment Groups were assembled recently to recommend a legal classification for each new species considered for NR 40 (Wisconsin’s Invasive Species Rule). They recommended that Vietnamese parsley be classified as prohibited based upon a literature review developed by the department.

Where substrates are loose and all fragments can be collected and disposed of, pulling or digging plants may be an effective control. However, this may not be practical for large populations. Given how new Vietnamese Parsley is as an invader in North America, there are few past control efforts from which to learn. However, good results may be achieved with aquatic formulations of translocating herbicides. Near Broadhead, a July application of 4 oz. AquatNeat® (glyphosate) concentrate and 1 oz. Habitat® (imazapyr) concentrate per gallon of water resulted in 75% efficacy after one treatment. Whether mechanical or chemical, control efforts should be followed by monitoring and spot-control.

SEWISC is currently working with the Wisconsin Department of Natural Resources (WDNR) to acquire funding for control efforts in 2017. At present, Vietnamese parsley is known to occur in a tributary to the Milwaukee River in northern Milwaukee County and several locations along the Bark River near Dousman in western Waukesha County. Help us identify any additional populations in southeastern Wisconsin and expedite early detection and rapid response efforts. Report any populations of this invading plant immediately to the WDNR. Digital photographs of leaves, stems, and flowers or fruits aid in the verification of reports of this species.