Weed of the Month (December 2010)
Henbit
By Peggy Wright
MG 2007
Photos by MG Herman Auer
Q
uestion: During the last two
winters, my lawn was overgrown
by weeds that grow in clumps. The weed
produced rather attractive flowers that
are purplish-colored and trumpet-shaped.
Should I be concerned with these clumps of
weeds?
Answer: The weed in question is very
likely to be Henbit (Lamium amplexicaule).
While several other weeds are more commonly known and present more widespread
problems in lawns, Henbit can spread aggressively if not properly managed. Henbit
has a strong preference for disturbed areas
(ex., bare spots, thinning lawn, etc.) and
edges of yards.
Henbit is native to Eurasia and Africa
and is thought to have arrived in the USA in
lawn seed during the 1920’s. It is a broadleaf
plant (dicot) that grows in clumps (Figure
1). Reproduction is primarily by seed but
it can reproduce vegetatively by the stems
rooting at the nodes. Henbit is classified
as a winter annual. Hence, homeowners
typically first observe it during late winter
and early spring in the Texas Upper Gulf
Coast region. While this weed is usually first
observed during late winter and early spring,
its seed germinates during early fall upon
the onset of cool temperatures.
Henbit is a member of the mint family
and has square stems. The first true leaves
are rounded and coarsely toothed with visible netted veins. On mature plants, lower
leaves are attached to leaves by short stalks
(know as petioles). The upper leaves where
the flowers occur lack petioles (know as sessile) and wrap around the stem. The leaves
are thick textured with pronounced veins
and circular in shape. Leaves occur opposite
(i.e., in pairs) along the stem and leaf margins have rounded teeth.
The attractive flowers are reddish
(especially unopened flowers, Figure 2) to
purplish when fully expanded (Figure 3),
slender, tubular (trumpet-shaped), 2‑lipped
and 1/2 to 3/4 inch (13 ‑ 19 mm) long.
Flowers are produced in a cluster with each
cluster containing 6‑12 flowers. Flower
clusters occur at the axil of a stem and upper
leaf. The blooming period occurs primarily during late winter and spring. However,
under our mild winter weather, some plants
also bloom during late fall for about a
month. Each flower typically produces four
triangular-shaped seeds nutlets (Figure 4).
Thus, a healthy plant is capable of producing hundreds of seeds!
Will henbit pose a problem in your lawn?
If the population is small, enjoy the flowers
for a bit but certainly do not let henbit set
seeds. Hand-pulling is a viable means of
control when only a few plants are involved.
Maintaining a healthy turf (including
proper fertilization) to provide competition
will help deter weed establishment. Regular
mowing at the proper height for the lawn
type can help minimize weed growth and
invasion in addition to reducing seed production. Remember, allowing a few plants
with pretty flowers to go to seed can result
in major infestations later on.
If henbit is a more serious problem in the
lawn, more aggressive control measures may
be in order. Several pre-emergent herbicides
provided good control of henbit. It is very
important that the pre-emergent application
coincide with the germination period of the
target weed or weeds. As stated, henbit is a
winter annual. It germinates with the onset
of cool weather conditions during fall. In
Galveston County, pre-emergent granular
herbicides should be applied during the first
two weeks of October.
Scientific
Name
Lamium amplexicaule
Other
Common
Name
Deadnettle, Common Henbit, Giraffe Head
& Henbit Deadnettle