Yellow woodsorrel (Oxalis stricta), also commonly called oxalis
or sheep sorrel, is a spring or summer annual weed throughout the south,
mid-west and eastern states. Yellow woodsorrel is a problem weed found in
lawns as well as in ornamental plantings. In lawns, the weed develops a
creeping growth habit often rooting at the nodes of low growing stems. In
ornamental beds or gardens the plant develops an upright or bushy growth
Description. Yellow woodsorrel leaves are divided into 3 heart-shaped leaflets, green to purplish in color, with long petioles attached to a weak, branching stem. Stems may be prostrate or erect up to 50 cm tall. Plants have a taproot, but some species spread by weak rhizomes.
Flowers of yellow woodsorrel have 5 bright yellow petals and are about 2 cm wide. Flowers develop in clusters in an unequally branched umbel. Seed develops in a slender capsule 5 to 15 mm long with 5 ridges and a pointed tip. Mature seed scatter several feet when the capsule bursts.
Control. Yellow woodsorrel is most effectively controlled by preemerge herbicides such as dacthal, oryzalin (Surflan), pendimethalin (Pre-M), isoxaben (Gallery), dithiopyr (Dimension) and oxadiazon (Ronstar). Preemerge products must be applied in early spring for effective control of early emerging weeds. Repeat applications may be needed with some products to obtain season long control.
Yellow woodsorrel is resistant to post emergent products such as 2,4-D and MCPP. Postemerge products containing dichlorprop (Weedone DPC) and triclopyr (Turflon D) are effective on yellow woodsorrel if applied early postemerge. Repeat applications may be required to control more mature plants.