Watercress

• Native to Western Asia, India, Europe and Northern Africa 
• Edible plant widely cultivated and commonly used as a salad green, garnish for meats and other dishes where a peppery or pungent flavor is desired.
• Member of the mustard family, which includes many well-known vegetables such as kale, turnips, and radishes, as well as many problematic weeds such as garlic mustard.
• Due to its wide acceptance as a naturalized species and use for food, there is little management except for instances of extreme conditions.
• Remains emergent and grows throughout the winter in waters that do not freeze.
• Primary pathway of introduction has been through the horticultural plant trade.  Watercress is able to escape cultivation via seed and vegetative reproduction, and may have been deliberately planted in streams.
• Utilizes allelochemicals as a deterrent for herbivorous invertebrate, this defense system is responsible for the spicy and peppery taste of watercress.
• Can become very invasive and outcompete other species in a stream. Watercress can become so dense that it blocks stream flow and floods adjacent meadows.

• Emergent, herbaceous perennial growing in wet environments with the ends of stems and leaves typically held above the water’s surface.
• Small white flowers are clustered at stem tips, flowers are on short stalks, have 4 white to purplish veined and tinged petals.  Flowers between March and October.
• Older leaves are compound with 3-11 leaflets, smooth or wavy edges, oval to lance-shaped with the terminal leaflet being the largest.  Young leaves are simple.  
• Usually observed growing as a tangle mass, stems are succulent and limp, except for tips which grow upright.  Stems are often floating, growing to 2 feet long and can freely root at the lower nodes, producing thin and fibrous roots.
• Fruits and seeds – flowers form thin, slightly curved, cylindrical pods that are 0.4 to 1 inch long and contain 4 rows of small, round seeds.

• Found growing in clumps in cold, gently flowing, shallow freshwater. Has less tolerance for stagnant or very fast moving water. 
• Habitats include lakes, reservoirs, streams, rivers and on damp soil.  Also found in mud along pond, marsh edges, and highway ditches.
• Areas of running water adjacent to springs and riverbanks or on wet soil.
• Abundant in nutrient rich waters and prefers abundant sunlight.
• Disturbance promotes watercress establishment.

• Watercress produces leafy shoots beginning in the spring, in late spring the plant begins to flower. Fruits ripen about two months after it flowers. Flowering ends in late summer, at which time it will again produce leafy shoots.
• Reproduces by seed and vegetatively.  
• Seeds are dispersed by wind, water, animals and humans. Seed float in water and germinate immediately.
• Vegetative reproduction can occur by stems falling over and forming adventitious roots or stem fragments that are dislodge from the parent plant and re-root at the nodes.
• Watercress will generally rely on reproduction by seed while in heavy vegetation will rely on vegetative reproduction strategies.

• Prevention is one of the most cost effective methods for invasive weed management.  Before moving from a contaminated areas make sure to clean and wash off clothing and boots.  Before moving watercraft or vehicles make sure to thoroughly clean all parts and equipment.
• Hand pulling and digging can be effective for smaller sized populations.  Carefully remove entire plant population, making sure to get as much root as possible.  Leave in piles in dry upland areas where stems will not re-root.  This method is labor intensive and costly. 

• Because watercress is an aquatic to semi-aquatic species special permits, pesticide endorsements and aquatic herbicides are legally required to apply herbicide. 
• Before applying herbicide contact your locally county noxious weed coordinator.
• Herbicides containing the following active ingredients are effective against Watercress:
  • Glyphosate (Non-selective, No residual soil activity)
    • Read herbicide label.
    • Apply 0.75% to 2% solution, equates to 1 fluid oz to 2.6 fluid oz per 1 gallon of water. 
    • Spray to wet but not to the point of runoff. Apply to actively growing foliage

• Bennett, M. (2007). MANAGING HIMALAYAN BLACKBERRY in western Oregon riparian areas. Oregon State University Extension Service, 1–16.
• Washington State Noxious Weed Control Board. (n.d.). Written Findings: Himalayan Blackberry. Retrieved April 8, 2020, from https://www.nwcb.wa.gov/images/weeds/Rubu_armeniacus.pdf
• DiTomaso, J.M., G.B. Kyser et al. 2013.  Weed Control in Natural Areas in the Western United States.  Weed Research and Information Center, University of California. 544 pp. 

Washington State Noxious Weed Control Board. (2008, December 9). Written Findings: Evergreen blackberry. Retrieved April 8, 2020, from https://www.nwcb.wa.gov/images/weeds/Rubus_laciniatus.pdf