The plant with the little purple flowers that have been showing up in home lawns is called henbit. If you are not sure this is what you have, check the stems. If they are square rather than round, you have henbit. A plant that also is low growing but has round stems and tiny white flowers is chickweed.
Both these plants are winter annuals and start to grow in the fall. They spend the winter as small plants and so most people do not pay much attention to them until they start to flower in the spring. Trying to kill either one at this late stage with a herbicide usually is a waste of time and money. Though plants may be burned back, they will rarely be killed. So what should you do? Remember, these are winter annuals that will die as soon as the weather turns hot. Keep the lawn mowed until nature takes its course.
However, you can do something next fall that will help the following spring. There are two possible courses of action, as far as chemical controls go. The first is to apply a preemergence herbicide in early to mid-September. This will prevent henbit and other winter annuals from germinating. Preemergence herbicides labeled for both henbit and chickweed include prodiamine (Barricade), dithiopyr (Dimension), isoxaben (Gallery), pendimethalin (Halts and others), oryzalin (Surflan and Weed Impede) and XL. All but Surflan, Weed Impede and XL are also labeled for speedwell. The second course of action is to wait until late October or early November (after most henbit has germinated) and use a postemergence broadleaf herbicide, such as those mentioned above. With this approach, most of the henbit will be killed but, because small numbers of henbit continue to germinate through the late fall and winter, some plants will be missed. This approach works well because henbit is relatively easy to kill in the fall and many people want to treat for dandelions at that time (i.e., October) anyway. Just remember you will have to do some spot-spraying in the spring if you want to get all the henbit. As a final note, henbit will not be very competitive in dense, healthy lawns, so good cultural management will reduce the need for herbicides.
Alicia Boor is an Agriculture and Natural Resources agent in the Cottonwood District (which includes Barton and Ellis counties) for K-State Research and Extension. You can contact her by e-mail at [email protected] or calling 620-793-1910. K-State Research and Extension is an equal opportunity employer and provider. Kansas State University, County Extension Councils, Extension Districts, and U.S. Department of Agriculture Cooperating.