Q. I have violets in a portion of my yard, and they are spreading as time goes on. Whatever my lawn care company is using on my lawn for weed control does not have any effect on these pesky weeds. Can you recommend anything that will eradicate them once and for all?
A. Violets are one of the toughest lawn weeds to control. They spread aggressively by thick, fleshy underground stems (rhizomes) that provide a large carbohydrate reserve. This ability to store carbohydrates allows them to resprout vigorously after you attempt to kill them. Violets can be controlled, but you have to go after them aggressively and keep after them. This is a process, not a one-shot treatment, and you will probably have to keep after them next spring, too.
The key to successfully controlling violets in turfgrass is proper timing of herbicide applications and making repeated applications until the carbohydrate reserves are exhausted. It is also important that the violets are actively growing and not stressed by drought; herbicide applications simply do not work as well otherwise. To protect your lawn, avoid spraying when temperatures are over 85 degrees, and never apply herbicides to your lawn when it is drought-stressed.
If violets have been a problem in your lawn for a while, there is a large seedbank in the soil as well. They will germinate and grow whenever they get a chance. To avoid that, it is important that you follow good cultural practices in caring for your lawn so that it grows thick enough to crowd and shade out any germinating violet seedlings.
Formulations of liquid broadleaf lawn weed herbicides will control violets if you make repeated applications in the spring when the violets begin to bloom. These are selective herbicides that kill broadleaf weeds without killing your lawn. It is likely that your lawn care operator is using the recommended 2,4-D, 2,4-DP and dicamba combination. However, it is very difficult for commercial lawn care companies to make repeated visits to your lawn at the 10- to 14-day intervals generally recommended between applications. They also may not be spraying at the absolute best time because visits are scheduled as part of a route. You may be able to get them to make extra applications at the suggested intervals, but you will have to pay for the service.
You could allow them to make their standard application, and then follow up yourself. Choose a product that actually lists "wild violet" as one of the weeds controlled on the label, such as Ortho Weed-B-Gon Chickweed, Clover and Oxalis Killer (triclopyr).
The best time to spray is when violets are in full bloom in May. The food reserves in the roots and rhizomes are at their lowest point because they have used those reserves to push out new growth and bloom in the spring. The idea is to hit them at their weakest point and to keep hitting them until they are under control. Follow the label directions on the herbicide as to intervals between applications and total number of applications allowed.
Ten to fourteen-day intervals are standard, so go with the shortest interval and keep on them until you are satisfied. Overseed any areas where the violets have crowded out the lawn to avoid bare spots. Nature abhors a vacuum, and germinating violet seeds will be happy to fill the void. Once the reseeded areas have matured enough to tolerate an herbicide application (follow label directions), you may need to spray again to kill any violets that grew along with the new grass. They are much more susceptible to control when they are small.
Obviously, we are past their peak bloom. Late August to early September offers another control window. At that time of year, plants translocate the carbohydrates produced through photosynthesis down to their rhizomes and roots to store for winter. Herbicides applied during this process are readily taken down to the roots, where they have a better chance of killing the roots and rhizomes. Expect to make at least two or three applications, so start early enough to allow sufficient intervals between application.
If the violets have completely crowded out areas of your lawn, you have the option of killing them with a nonselective herbicide such as Round Up (glyphosate) or one of the many Round Up knockoffs available because glyphosate went off patent. Although it will kill any grass as well as the violets, it is often the best solution if there is not much grass left. Then reseed the area with good grass seed that matches the rest of your lawn.
If the violets are creeping into your lawn from a neighbor's who does not wish to control them, you will be fighting a never-ending battle. Many people enjoy their pretty flowers in the spring and appreciate such diversity in their lawn.
First Published: July 4, 2009, 4:00 a.m.
