Field pansy flowers and leaves closely resemble those of the garden flower Johnny-jump-ups. Flowers are cream to blue, often with both colors mixed in varying patterns within the flower. Flowers have five petals, with the lowest petal having a cup-like projection extending to the back of the flower. Leaf shape varies, with the lowest leaves being rounded, and upper leaves being narrower at the base than at the tip of the leaf. At the base of each leaf, smaller, highly divided sets of leaf-like stipules are found.
Field pansy plants are four to ten inches tall. They generally grow in groups, right in and among strawberry plants.
Field pansy is a winter annual weed. This means that it is one of a class of plants that germinates in the late summer or fall, overwinters as a seedling or small plant, and then continues growth in the spring. Winter annuals cannot withstand hot weather, and generally set seed and die as summer weather begins. Winter annuals are problem weeds for strawberry growers for several reasons. First, the lack of fall or spring tillage in strawberries means that the growth of winter annuals is not disturbed. Second, winter mulch provides protection for these weeds, and increases winter survival. And third, renovation does not affect winter annual weeds, as they have usually produced seed and died by the time renovation is performed. Renovation does disturb summer annual weeds (weeds which germinate in the spring and die in the fall), so winter annual weeds tend to become dominant in strawberries.
Field pansy is closely related to violets, pansies, and Johnny-jump-ups. Field pansy seeds germinate in mid-to-late fall or in the early spring. Flowering begins in May and continues through early June. Seed capsules are brown and split open in dry weather, throwing large numbers of small brown seeds some distance from the plant.
Field pansy is low-growing and probably does not compete significantly with strawberry plants for light. On some farms, however, this weed is present in such high numbers that it is clearly a significant nuisance. In addition, at very high numbers, field pansy may be competing with strawberries for moisture and nutrients. This weed spreads extremely quickly and is very hard to control. For this reason, it may be worthwhile to scout for this weed and eliminate it if it appears in strawberry fields. Elimination of this weed before it is able to produce seeds can prevent future problems.
Chemical: There is no post emergence herbicide available at the present time to control field pansy in strawberries. Among the pre emergence herbicides, only Dacthal has any effectiveness against field pansy. Even this control method, however, is imperfect. Dacthal has an extremely short lifespan in the soil, providing residual control of this weed for only four to six weeks. Because germination and emergence of field pansy continues throughout the fall, later- germinating weeds will escape control with Dacthal. Dacthal’s high cost may make it difficult to justify.
Nonchemical: Field pansy can be controlled non-chemically with rotation, cultivation and hand control, or combinations. Cultivation will control weeds only between rows. Field pansy is most often found growing in and among strawberry plants, and weeds in this area must be removed by hoeing and hand-pulling. Rotation can also be used to manage this weed. Winter annual weeds generally do not do well in most vegetable crops. Tillage in the fall and spring will destroy both fall and spring-germinating weeds. Rotating out of strawberries for several years should greatly reduce the number of field pansy seeds in the soil. This should reduce the potential of this weed to build up to levels at which it reduces yields.
Integrating chemical and nonchemical controls: It may be possible to boost the effectiveness of Dacthal by controlling field pansy with cultivation and hand weeding until mid-September, then applying the herbicide. This should allow the Dacthal to control emerging seedlings through the end of the season. Any seedlings, which escape control, can be controlled by hand before mulch is applied in the fall or in early-to-mid spring. Control in the spring should preferably be completed before seed production begins in mid- to late-May. Management decisions with this weed will have to balance economics and the potential of this weed to reduce income. On farms where field pansy numbers are low or where the weed has recently invaded, it may be worthwhile to take extraordinary measures to eliminate this weed. Extra time spent hoeing and/or herbicide applications may prevent a small problem from increasing to one of major proportions. Where rotation is possible, this may be the most cost-effective way of coping with this weed.
By: M.J. Else and A.R. Bonanno, University of Massachusetts
Reviewed by: Mary Concklin, UConn IPM. 2012
The information in this document is for educational purposes only. The recommendations contained are based on the best available knowledge at the time of publication. 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. The University of Connecticut, Cooperative Extension System, College of Agriculture and Natural Resources is an equal opportunity program provider and employer.