Deadnettle (Lamium amplexicaule L).

Deadnettle is also known as Henbit and Henbit Deadnettle. It is a cool season annual that has the name “Deadnettle” because it looks like stinging nettles, but without the sting (hence the term “Dead”).

It is a common, low growing weed that is very competitive in turf. Deadnettle can also cause staggers in livestock, with sheep being the most susceptible.

Henbit Deadnettle has hollow stems that have a square cross section. The upper leaf surfaces and prominent veins on the underside of the leaf have a cover of fuzzy hairs.

Being a Winter annual, Deadnettle germinates in the Autumn, survives over Winter, and then flowers and develops seeds. Once temperatures rise in the late Spring and early Summer it dies off. It is found in all States and Territories in Australia, including the ACT and Red Hill.

For more information, please check out our weed ID chart. Deadnettle is a good indicator weed of cooler, wetter areas.

The distribution map for Henbit is courtesy of The Atlas of Living Australia.

 After you finish reading this, you will be able to:

• Identify Henbit Deadnettle.
• Know the habitat of Henbit Deadnettle.
• Know the best cultural and chemical options to control Henbit Deadnettle.

Henbit Deadnettle Identification.

It is mistaken for Creeping Charlie as both have square stems, are members of the mint family and have small purple flowers. However the key difference is Henbit Deadnettle is an annual that flowers in early Spring, and then dies in late Spring. Creeping Charlie is a perennial that flowers in the late Spring.

Category: Herb

Photosynthetic Pathway: Deadnettle is a C3 Weed.

Flower: Henbit has clusters of about 12 pink-purple tube shaped flowers, that are 1.5 to 2 cm long, and blooms in the Spring.

Height: Often grows up to 10 to 25 cm tall

Leaves: Deadnettle leaves are 2 to 3 cm in size. They are opposite in pairs, and each pair of leaves is at 90° to the pair below it. It does not form a rosette.

Reproduction: Henbit reproduces by seed, but it also grows and spreads from stem fragments. Newly shed seeds are dormant, and require one or more winters before they germinate.

• Seed longevity: >5 years
• Seeds/plant: 200

Root System: Deadnettle has a fibrous root system, with a taproot that is up to 20 cm long.

Comments:

• Deadnettle has soft, hairy stems, that emerge from the base of the plant.
• The stems are often purplish, and the leaves are aromatic when you rub them.
• A good way to identify this weed is that the upper leaves are more purple-red than the lower leaves.
• The upper leaves of Deadnettle attach directly to the stem.
• The lower leaves have petioles.
• It is frost and drought tolerant but does not tolerate shade.

Habitat: You find Deadnettle in open disturbed sites, in fields and along roadsides, and also in lawns.

Being a Winter annual and biannual broadleaf weed, Deadnettle grows during any period of warm weather over the Winter. Henbit Deadnettle resumes growth and produces seed in the Spring, and then dies as temperatures increase in late Spring and early Summer.

Henbit Deadnettle quickly invades thin turf areas, especially where there is overly moist soil. Its growth habit may be prostrate, so plants are not affected by mowing.

In the absence of pre-emergent herbicides, early Spring vertical mowing and hollow-tine aeration increase Henbit in thin turf areas. This emphasises the need to properly maintain your turf.

First, select a turfgrass cultivar adapted for your area, and then properly fertilize, mow, and irrigate to encourage dense growth. Water the lawn deeply but as infrequently as possible in the Autumn, as weed seeds need soil surface moisture to germinate.

You can pull small numbers by hand.

Always aim to implement cultural controls before you use herbicides for Deadnettle control. However, chemical control may still be necessary even if you modify your lawn care techniques to try and manage this weed.

Also, as it it is a Winter annual, it will naturally die in the Summer so you probably don’t need to apply herbicides in the late Spring. You can see heat stress kicking in when the leaves start to turn yellow.

Pre-Emergent Control for Deadnettle.

• Battalia 435
• Envu Esplanade
• BASF Freehand.
• Metolachlor

Post Emergent Control of Deadnettle.

The ideal time for control with a post-emergent herbicide is when it is small and actively growing. This is typically in the late Autumn after weed germination, but before temperatures begin to drop and plant growth significantly slows (air temperature needs to be above 10° C).

Apply chemical controls in the Autumn or early Spring for best results. Keep in mind that herbicide effectiveness reduces as this weed matures.

When you see Henbit flowering in the Spring, like other winter annual weeds, it is then very difficult to control. At this stage it is likely to be too late to prevent the production of viable seed.

Control of Henbit is best with a pre-emergent in the late Summer or early Autumn. You can use a post emergence after it emerges in the mid to late Autumn.

If you do make Spring applications make sure you do these before it flowers. A three-way herbicide is most commonly applied for control.

There are a few selective post-emergents that control this weed. Products containing MCPA, and Dicamba usually provide better results. Treatment is best over the entire area rather than spot treating.

• Dicamba (Do not use Dicamba on Buffalo grass)
• Warhead Trio. Safe to use on Buffalo grass.
• Stature Herbicide. Not for use in the home garden.
• QualiPro Negate. Not for use on Buffalo, but is safe on warm season turf grasses like Couch and Zoysia.
• Bispyribac Sodium in the USA.
• Foramsulfuron in the USA.
• Metribuzin
• Trifloxysulfuron in the USA.
• Iodosulfuron in NZ.