Botanical name: Veronica filiformis
Aliases: Creeping Speedwell, Threadstalk Speedwell, Round-Leaved Speedwell, Whetzel Weed
Slender speedwell is the most common of the speedwell family that that is found in managed turf.
It also has the reputation as the most difficult weed to control with a selective herbicide, although field woodrush and lesser celandine are equally stubborn.
This perennial weed was introduced into the UK from Turkey. It’s original role was as a rock garden plant, but it didn’t take gardeners long to discover how invasive it could be, and it soon became a major weed in fine turf.
Slender speedwell is a low growing weed, that will happily tolerate even the lowest mowing heights. It spreads by producing both overground (stolons) and underground (rhizomes) runners that root at the nodes. Speedwell rarely reproduces from seed as it is a self pollinating plant.
It can also spread by small, loose fragments of the plant that is dispersed by the mower, this helps it colonise areas of the lawn as it quickly becomes a nuisance by forming large patches. It is not a fussy weed and will thrive in any type of soil condition.
Slender Speedwell identification
- Leaves: The small, light green leaves measure up to 10 mm across and are opposite. They are round or kidney shaped, with slightly scalloped edges and borne on a short stalk.
- Flowers: The small flowers are lilac – light blue in colour, with four petals, with one petal being noticeably smaller than the remaining three. They can measure up to 10 mm in diameter, flowering between the months of April and July.
- Roots: This weed has a shallow and fibrous root system.
Slender Speedwell Images (click image to enlarge)
Prevention and control
Encourage a healthy sward with good turf care practices. This includes a balanced feed program, regular scarification and aeration and the correct mowing regime to help prevent this weed from encroaching.
Ensure the grass clipping are boxed of and removed (avoid using for compost) when mowing, as slender speedwell can spread by loose fragments, that are returned to the turf.
Raking this weed into an upright position prior to mowing can help remove part of the plant and weaken it somewhat.
Mow regularly to prevent speedwell from flowering.
Be vigilant and remove individual plants when they appear, as this weed will spread rapidly forming large patches in a short period.
A treatment of lawn sand early spring will help burn off the leaves (although it won’t kill the plant), weakening it. Lawn sand is often applied at this time of the year, as it is a popular way of controlling moss in turf.
As we previously noted, slender speedwell is notoriously difficult to control with chemicals, as it is resistant to most active ingredients used in herbicides. If you intend to go down the chemical route, choose a product that contains fluroxypyr. Fluroxypyr has been proven to be the most effective chemical in controlling speedwell.
Below are a list of products recommended for the control of this weed. More than one application will be required and even then, the weed may still persist.
Recommended products for slender speedwell control
Professional products (The user requires the appropriate certificate/s to apply these products)
Headland Cabadex (Fluroxypyr, Flurosulam)
Everris Praxys (Clopyralid, Fluroxypyr, Fluosulam)
Barclay Holster XL (2,4-D, Fluroxypyr, Dicamba)
Mascot Greenor (Clopyralid, Fluroxypyr, MCPA)
Products available for non-professional use (These products are available from garden centres and DIY stores)
Verdone extra (Clopyralid, Fluroxypyr, MCPA)
Weedol lawn weed killer (Clopyralid, Fluroxypyr, MCPA)