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Corn speedwell is a winter annual weed that is classified by herbicide manufacturers as hard to control.
It is not usually found in thick, healthy lawns but can be a problem in thin, weak grass stands and newly seeded areas; where it is capable of forming dense mats.
Many of the pictures below were taken in shady areas, under pine trees and on the outskirts of highly maintained park lawns. I have also found it overtaking neglected lawns, in landscape beds, and growing in sidewalk cracks.
Like many other Veronicas, this is a cute little plant with tiny, bright blue flowers; however, it is very is invasive and found on noxious weed lists.
There are several Speedwell species of the Veronica genus that
are used in ornamental plantings; however, many are invasive and weedy.
Corn speedwell is one of the most prevalent of the weedy species,
others include: Germander, Persian, Creeping, Purslane and Ivyleaf.
Typically, winter annual weed seeds germinate in the fall and grow
throughout the "warmer" days of winter. They continue active growth in
early spring, flower, set seed and then die as the temperatures rise
into the summer.
Looks like and sometimes confused as:
What to look for:
Pictures of Corn Speedwell
Cultural Control: Corn speedwell only spreads by seed and is very aggressive in stressed, thin and newly seeded turfgrass stands or other areas with exposed bare ground such as landscape beds that are not mulched.
Seeds need contact with soil, sunlight and moisture to sprout and grow; therefore, mulched landscape beds and sound lawn maintenance practices--watering, mowing fertilizing--encouraging a healthy, dense lawn will suppress this weed.
Mechanical Control: A simply way to control a few weeds in the landscape is by hand weeding.
Speedwell has a fibrous root system and is easily pulled by hand, especially when the soil is moist. It will not re-grow from the roots so hand weeding is effective as long as all of the leaves and stems are removed.
Chemical Control: Corn Speedwell is classified as hard to control with herbicides. The most effective approach is to apply pre-emergence herbicides in the fall to prevent seeds from sprouting. Winter annual weed seeds germinate in the fall, therefore, this is the best time to prevent them with pre-emergence herbicides.
Attempts to kill this weed in late spring usually fail because it is at the end of its life cycle. Optimum control with post-emergent herbicides is gained when applied in early spring when it is actively growing, and this is between the four leaf and flowering stage.
Broadleaf herbicides for Speedwell control:
(As recommended by N.C. State Turffiles)
One application of the following:
Lawn care professionals, who have successfully killed this weed with herbicides, recommend using a backpack sprayer or hand can with a flat-fan type nozzle that produces fine droplets. The small droplets will give better coverage of this tiny weed and adhere to the leaves better. Adding a surfactant to the herbicide mix will also improve results.