Yellow Woodsorrel - Weed of the Week

The Three-hearted Scoundrel

A much-dreaded weed of nursery workers, greenhouse managers and landscapers, yellow woodsorrel (Oxalis stricta) boasts its heart-shaped leaflets and bright yellow flowers in lawns and gardens during warm months of the year. It is a weak perennial capable of spreading by virtue of its rhizomes, as well as by seeds that can readily germinate. Due to a distinctive sour taste, it is sometimes referred to as sour-grass, and its name even derives from the Greek word “oxus,” which means sour. The sour nature of this weed can be attributed to oxalic acid present in the members of its family, Oxalidaceae. Creeping woodsorrel (Oxalis corniculata) is a closely related species, but it grows more procumbent to the ground and spreads by stolons.

The exact origin of yellow woodsorrel is unclear. Some consider it native to North America, whereas others have reported it to be of East Asian origin. It is considered to possess antiseptic properties and to soothe throat and stomach discomforts. Although it is edible in small quantities, large quantities can be toxic due to its oxalic acid content. Fresh yellow woodsorrel leaves are sometimes used as a garnish in salads to give it a tangy flavor.

Yellow Woodsorrel Identification

Yellow woodsorrel is characterized by light green stems that are sometimes purple at the lower part, often unbranched, giving rise to tri-compound leaves with long petioles and heart-shaped leaflets. The heart-shaped leaflets help to distinguish it from clover leaves, which are not heart-shaped but look similar otherwise. Its leaves usually fold up during nighttime and unfurl by day to photosynthesize. Flowers are marked by five bright yellow petals. Seeds are oval-shaped and yellow when ripe and are characterized by a hard, ribbed, sticky seed coat, allowing it to grip on to surfaces, such as farm machinery and containers. Yellow woodsorrel seeds are borne in cylindrical seedpods that are about ½ inch long, resembling a miniature okra, capable of bursting open and dispersing the seeds 10 to 15 feet away. Lower nodes produce slender adventitious roots. Yellow woodsorrel usually attains a height up to 8 inches, but it can grow taller in certain environments. Seeds do not require a dormancy period prior to germination. Light is a requirement for germination, which occurs between 60°F and 80°F (15°C to 26°C).

Controls for Yellow Woodsorrel

Hand-weeding or mechanical removal can be tedious, but it is effective if all the rhizomes are completely removed from the soil. Shallow tilling can aggravate the problem by breaking up and spreading the vegetative parts. Landscape fabric or other impervious mulches can be effective. In landscapes and nurseries, the pre-emergent herbicides indaziflam (Marengo), isoxaben (Gallery, component of Snapshot TG) and oryzalin (Surflan) effectively control this weed prior to germination. Indaziflam can control it when applied during early stages of growth as well. Pre-emergent herbicides, such as isoxaben (Gallery), pendimethalin (Pendulum) or dithiopyr (Dimension) are effective to prevent establishment from seeds in cool-season turf. In landscapes and nurseries, once the weed has emerged, using a hand-held weed wiper to carefully apply glyphosate (Roundup or other formulations) can be effective to manage yellow woodsorrel. Application of a systemic herbicide containing triclopyr or 2,4-D + dicamba can help control yellow woodsorrel after it emerges in turf.

Author:  Rakesh Chandran, WVU Extension Weed Science Specialist 
Last Reviewed: September 2020

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