Spring Brings a Purple Haze

Spring Brings a Purple Haze

By Heather Benedict, Agronomy Specialist

The weather is finally cooperating. People all over Missouri are spending more time outdoors in their fields, yards or gardens. Something you may have noticed is a purple haze over parts of the landscape. This is due to one or several different weeds. Purple deadnettle (Lamium purpureum) and henbit (Lamium amplexicaule) are both low growing plants with tiny purple flowers.

Purple deadnettle, and henbit are winter annual type plants. This means they germinate in the fall or late winter. They generally bloom in the spring, produce seed and then the plants die. Both Purple deadnettle and henbit are in the mint family, so when crushed or mowed, they produce a slightly minty scent. Both types of weed have square stems. The difference between them is in the shape of the leaves. Henbit has rounded leaves and darker purple flowers. Purple deadnettle has pointed leaves and pale flowers. The top leaves of purple deadnettle can also be a purplish color.

In crop fields, these types of weeds are not very competitive for moisture or for nutrients. The crop that may be most affected by henbit is wheat. Researchers in Missouri have found that henbit in densities of 82 plants per square foot can result in yield reductions. However, densities of 18 plants per square foot do not show any yield reduction. The fact that henbit dies off quickly in the spring, has led researchers to look into using it as a ground cover for row crops. However, there is some concern with using henbit as a ground cover for soybeans as it is a host for the soybean cyst nematode. In order to decrease the damage to yield from the nematodes, a good rotation system should be used. In the rotation system, henbit is not a good option.

In pastures henbit is surprisingly digestible with relatively high protein values. Henbit has been shown to have protein values comparable to tall fescue. Henbit is also palatable for animals and can be used for grazing until later maturing species come on. The drawback to using henbit or even chickweed in a pasture system is that they are not high producing.

For home owners, these weeds can be a nuisance. They spread quickly and easily. Also, they are most noticeable in the spring when they are difficult to control. 2,4-D herbicides may be used to help control purple deadnettle and henbit, however that type of herbicide is volatile and can easily injure or kill, tomatoes, flowers, grapes, and other garden vegetables. Another option for control is to use a pre-emergent herbicide on the lawn in the fall.