There are several species of yellow wood sorrel. All are similar in appearance. Leaves are a bright, light green and are divided in three heart-shaped parts. Although they are lighter green in color, leaves are otherwise quite similar to those of clover. Leaves are often folded downward, giving them the appearance of a closed umbrella. Flowers are a bright golden yellow, with five petals. Size and growth habit of the plant vary considerably. Plants generally grow upright, but have weak stems and may creep along the ground. Entire plants are generally no more than eight inches tall. Yellow wood sorrel is most often found growing right in and among strawberry plants.
Yellow wood sorrel is an extremely common weed in Massachusetts strawberry plantings. Plants are able to grow in and among strawberry plants, thriving in the shade cast by the strawberry leaves. This makes them difficult to kill with hand weeding, hoeing and herbicides. Yellow wood sorrel is low-growing and shallow-rooted, and probably does not compete with strawberries for light, but at extremely high densities it may compete with the crop for water and nutrients. In addition, dense growth of this weed can make it hard for pickers to find fruit and may block air flow, making plants more susceptible to fungal diseases. Although this weed is fairly attractive, large quantities of it would probably be considered unsightly in a pick-your-own field.
In Massachusetts, the most frequently-found species of yellow wood sorrel is common yellow wood sorrel, Oxalis stricta. This species of yellow wood sorrel is a perennial. Common yellow wood sorrel is a simple perennial, meaning that it spreads only by seed. Plants pulled up will often have a thickened pinkish root, which enables it to survive the winter. Common yellow wood sorrel does not have runners. Seeds are contained in an upright pod which starts out green, then matures to a light green or brown color. When the pod is dry, it will split open along seams, forcefully throwing its small, red-brown seeds from the plant. This enables yellow wood sorrel to colonize new areas of the field. Yellow wood sorrel spreads extremely quickly. Within a few years, a small infestation can fill an entire field.
Yellow wood sorrel is edible. The green seed pods, leaves and stems can be eaten in salads. Plants have a pleasant lemony taste and will quench thirst on hot summer days. Yellow wood sorrel contains oxalic acid, which can be toxic if consumed in large quantities.
Chemical: Germination of seeds of yellow wood sorrel takes place over a long period of time through the year. This makes control with pre emergence herbicides difficult. Sinbar is the only pre emergence herbicide currently registered for use in strawberry which provides some control of yellow wood sorrel. At registered rates, however, control is usually less than adequate. Splitting the annual use rate of Sinbar into a renovation and late fall application is recommended. The late fall application should be made after plants become dormant. Some post emergence control can be obtained with 2,4-D. Plants will be controlled only if they are small and not hidden under strawberry foliage. The application should be made prior to mulching, over dormant strawberry plants. Strawberry plants are dormant when leaves have developed a reddish color and plants become flattened in appearance. A 2,4-D application prior to renovation is usually not effective, since plants have already produced and dispersed their seeds by early summer.
Nonchemical: Growers who do not yet have yellow wood sorrel should consider scouting for it on a yearly basis. Scouting can serve as an early warning signal for this and other troublesome strawberry weeds. Removing this weed by hand when it first appears in a strawberry bed can prevent a small problem from becoming a big one. Similarly, growers with multiple plantings may want to consider cleaning equipment when moving from infested fields to fields free of this weed. Small numbers of this weed can probably be eradicated from plantings through frequent and vigilant hand weeding. Rotating to crops other than strawberries for several years should also make a big dent in the population of yellow wood sorrel seeds in the soil.
Integrating chemical and nonchemical control: Combining chemical and nonchemical approaches may be the most economical way to attack yellow wood sorrel. Partial control can be obtained with the herbicides described above. Control of plants which escape these herbicides can be obtained with nonchemical measures such as cultivation, mulching, hoeing and hand weeding. Rotating to other crops as often and for as long as possible should also be of great help in reducing problems caused by yellow wood sorrel and many other strawberry weeds.
M.J. Else and A.R.Bonanno, University of Massachusetts Extension
The information in this material is for educational purposes. The recommendations contained are based on the best available knowledge at the time of printing. Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension system does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available.All agrochemicals/pesticides listed are registered for suggested uses in accordance with federal and Connecticut state laws and regulations as of the date of printing. If the information does not agree with current labeling, follow the label instructions. The label is the law.Warning! Agrochemicals/pesticides are dangerous. Read and follow all instructions and safety precautions on labels. Carefully handle and store agrochemicals/pesticides in originally labeled containers immediately in a safe manner and place. Contact the Connecticut Department of Environmental Protection for current regulations.The user of this information assumes all risks for personal injury or property damage.Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Kirklyn M. Kerr, Director, Cooperative Extension System, The University of Connecticut, Storrs. The Connecticut Cooperative Extension System offers its programs to persons regardless of race, color, national origin, sex, age or disability and is an equal opportunity employer.