Pre and Post Emergence In the Garden

by: Dr. Mario Villarino, Agri-Life Extension Agent

Certainly it has been a busy time for us at the Hopkins County Extension Office. With most of our 4-h livestock projects finishing at the NETLA Livestock Show, our activities for the spring start gearing up. A common question that I often get is when and what to use to control weeds. There are basically two types of weed control chemicals in the market: those that act before the plant germinates (pre-emergent), and those that act once the weeds are actually visible (post emergent).

If you can actually see the weeds, you have to apply a post-emergence herbicide to control them. So, the logical question pops out: "If you do not see the weeds, why control them?"

The answer to the question has to do with success. It is always a lot easier to prevent than to control. Pre-emergent herbicides are more successful than post emergent herbicides are more successful when the weeds are small. The last drought, lack of a cold winter, and milder summery days have triggered many weed plants in our yards, including "henbit."

Henbit (Lamium amplexicaule) is a cool season annual broadleaf weed. Seedlings begin to emerge in early fall and grow throughout the autumn season, winter, and spring. Henbit can dominate turfgrass in the spring, throughot the southern region of the U.S. Although henbit is not know for an herbal or medicinal purposes, this plant is used in flower arrangements because of its unusual leaf shape and arrangement. Henbit, a member of the mint family, has characteristic square stems. Stems are slender, ascending or prostrate, and freely branched at the base. Stems may root at the lower nodes. Leaves are opposite, nearly circular, deeply veined, hairy, and petioled. Upper leaves clasp the stem and the lower leaves are distinctly petioled. Roots are shallow and fibrous. Flowers, conspicuous in early spring, are tubular, pink to purple, and borne in the leaf axile. Seeds are borne in a pod.

Henbit is most effectively controlled with herbicides in the fall while plants are small and immature. Products containing dicamba, MCPP, and 2,4-D have demonstrated effective control in the fall and early spring. In dormant bermudagrass, glyphosate, diquat or metribuzin will control henbit. If applied prior to germination, products such as surflan, bensulide, pendimethalin, and simazine also proved good control of henbit. Follow label directions on all  products recommended for henbit to obtain the best control.

For most of the gardens in our area, the only alternative is to use post-emergent now and pre-emergent next fall. But remember that controlling a smaller plant will take less chemical and is better for the environment. If the weeds are fully grown, a lawn mower with a grass catcher might be your only option. You can always feed the clipping to chickens, since poultry really enjoy henbit as a treat. For more information on this or other agricultural topis, please call the Hopkins County Extension Office, at (903)885-3443.

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