Figure 1. Thyme-leaf speedwell growing in shaded area of a lawn. Photo by Peter Landschoot, Penn State

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This species is often found growing in moist soils and shaded areas with thin turf. It tends to grow in diffuse patches and is most conspicuous when flowering during spring.

Life Cycle

Thyme-leaf speedwell (Veronica serpyllifolia L.) is a member of the plantain family (Plantaginaceae) and is classified as a perennial. Plants produce stolons (runners) that creep in prostrate fashion and form new roots and leaves at nodes. This species produces flowers, fruits, and seeds during early to mid-spring.

Figure 2. Thyme-leaf speedwell stolon producing roots and leaves at nodes. Photo by Peter Landschoot, Penn State

Identification

Thyme-leaf speedwell stems are hairless, and initially grow close to the ground then turn upright, giving rise to flowers and seed-bearing fruits. Flower stems do not branch and can grow up to 12 inches tall. Leaves are oval or oblong and grow opposite one another on stems. Lower leaves are larger (½ to 1 inch in length and about a ½ inch wide) than leaves growing on upper portions of stems. Leaf margins of thyme-leaf speedwell are smooth, and leaf surfaces lack hairs; whereas common field speedwell and corn speedwell have serrated leaf margins and leaves with hairs on the surface.

Figure 3. Leaves of thyme-leaf speedwell lack hairs, have smooth margins and are opposite one another on stems. Photos by Peter Landschoot, Penn State

Flowers develop on stalks that arise from leaf axils on stems and are very small, usually ⅛ to ¼ inch across. Each flower has four white petals (one petal is smaller than the others) with dark blue or purple longitudinal stripes. Like other speedwells, each flower has two stamens and a single style. Thyme-leaf speedwell flowers are replaced by heart-shaped fruits that contain seeds.

Flowers (left) and fruits (right) of thyme-leaf speedwell — Figure 4. Flowers of thyme-leaf speedwell (left) and heart-shaped fruits (right) on short stems arising from leaf axils. Photos by Peter Landschoot, Penn State

Management and Control

The occurrence of thyme-leaf speedwell can be reduced by improving turf density through fertilization, regular mowing, and the use of turfgrasses well-adapted to site conditions. This weed can be suppressed or controlled with various preemergence and postemergence herbicides.

Table 1. Preemergence herbicide products labeled for control of thyme-leaf speedwell.
Active ingredients	Product name(s)*
isoxaben	Gallery 75 Dry Flowable, Isoxaben 75WG
prodiamine and quinclorac	Cavalcade PQ
sulfentrazone and prodiamine	Echelon 4SC
oxydiazon	Oxadiazon 2G, Oxadiazon SC, Ronstar FLO, Ronstar G

*Follow label precautionary statements, restrictions, and directions regarding tolerant turfgrass species, rates, and timing of applications. Active ingredients and products in bold type contain a specific reference to thyme-leaf speedwell on the label. Other labels list speedwell but do not specify the individual species.

Table 2. Postemergence herbicide products labeled for control of thyme-leaf speedwell.
Active ingredients	Product name(s)*
2,4-D	Clean Amine, Hardball, Weedar 64, WEEDestroy AM-40
2,4-D, clopyralid, and dicamba	Millennium Ultra 2**
2,4-D, fluroxypyr, and dicamba	Escalade 2
2,4-D, fluroxypyr, triclopyr, and flumioxazin	Sure Power (ester formulation)
2,4-D, MCPP, dicamba	Threesome, Lesco Three-Way, 3-D
2,4-D, quinclorac, and dicamba	Quincept; 2DQ Herbicide; Triad QC Select
quinclorac, sulfentrazone, 2,4-D, and dicamba	Q4 Plus
2,4-D and triclopyr	Chaser 2 Amine, Turflon II Amine
2,4-D, triclopyr, and fluroxypyr	Momentum FX2
2,4-D, triclopyr, fluroxypyr, and sulfentrazone	Momentum 4-Score
2,4-D, triclopyr, dicamba, and pyraflufen-ethyl	4-Speed XT (Isooctyl ester formulation)
2,4-D, triclopyr, dicamba, and sulfentrazone	Foundation
amicarbizone	Xonerate 2SC
carfentrazone-ethyl and quinclorac	SquareOne
fluroxypyr and triclopyr	Tailspin
MCPA, fluroxypyr, and dicamba	Change Up
MCPA, fluroxypyr, and triclopyr	Battleship III
MCPA, MCPP, and dicamba	Tri-Power
MCPA, triclopyr, and dicamba	Lesco Three-Way Ester II (ester formulation)
MCPA, triclopyr, and dicamba	Eliminate, Horsepower
quinclorac	Drive XLR8, Quinclorac 1.5 L, Quinclorac 75 DF
sulfentrazone	Surepyc
sulfentrazone and carfentrazone-ethyl	Dismiss NXT
sulfentrazone and quinclorac	Solitare, Solitare WSL
triclopyr and sulfentrazone	Tzone SE

*Follow label precautionary statements, restrictions, and directions regarding tolerant turfgrass species, rates, and timing of applications. Active ingredients and products in bold type contain a specific reference to thyme-leaf speedwell on the label. Other labels list speedwell but do not specify the individual species.

**Clopyralid-containing products should not be used on residential lawns but can be used for treating weeds in non-residential turf.

References

Anonymous. Thymeleaf speedwell (Veronica serpyllifolia). The University of California Agriculture and Natural Resources Integrated Pest Management Program.

Hilty, J., 2017. Illinois Wildflowers. Thyme-leaved speedwell.

Agenda

Authors