Oxalis/yellow woodsorrel

Oxalis/yellow woodsorrel

The issue: Oxalis or yellow woodsorrel (Oxalis stricta) is a weak perennial, native to eastern and central U.S. that is more of a lawn, yard and garden weed, but can invade woodlands, meadows, and field crops as well. It prefers moist soils but tolerates dry soils once established. Oxalis is most often introduced to an area from bedding plants and nursery stock.

The trifoliate leaves have a long petiole and are similar to clover and shamrock leaves, but the leaflets are more heart-shaped. The leaflets fold in half during the night. The yellow, five-petaled flowers are about a half inch across and give rise to a five-ridged, torpedo-shaped seedpod that is held mostly upright. It can grow up to a foot tall, but as the stems lay along the ground it may root at the nodes.

Oxalis reproduces by seed, rhizomes and stolons. Mature seedpods rupture, expelling seeds up to 16 feet away. The seeds require light to germinate. Control efforts must focus on eliminating seed production and spread.

Integrated pest management options:

· Prevention: Check bedding plants and nursery trees and shrubs. Watch new plantings for germinating oxalis and remove immediately.

· Mechanical: Hand dig new and small infestations before seed production.

· Cultural: Set mower height no lower than 2.5 inches; provide growing conditions for healthy competition; organic mulch at least 3 inches deep.

· Biological: None.

· Chemical: Pre-emergent herbicides with dithiopyr, pendimethalin, prodiamine, or isoxaben are labeled for oxalis; post-emergent herbicides with 2,4-D, dicamba, MCPP—don’t apply when temperatures will be above 85 degrees for three days. Be sure the target weed and crop, or landscape situations are listed on the product label. Always read and follow herbicide label directions.

Combine them: These control options are all more effective when combined with the other efforts described.

For more information, contact Ron Patterson, University of Idaho Extension horticulture/agriculture educator in Bonneville County, at 208-529-1390 or rpatterson@uidaho.edu.