Deadnettles

Images above: Upper Left: Henbit seedling (Scott Morris, Cornell University). Upper Right: Henbit plant (Scott Morris, Cornell University). Bottom: Henbit flower (Scott Morris, Cornell University).

Images above: Left: Purple deadnettle seedling (Scott Morris, Cornell University). Right: Purple deadnettle plants (Scott Morris, Cornell University).

Identification

Other common names:

• Henbit:  bee nettle, blind nettle, giraffe head, dead nettle, henbit dead-nettle, henbit-nettle
• Purple deadnettle:  red deadnettle

Family:  mint family, Lamiaceae

Habit:  Henbit – winter annual or summer annual, sprawling with upward curving stems that root at the nodes.  Purple deadnettle – sprawling winter annual with stems rooting at the nodes.

Description:  Seedlings have stalked cotyledons with two lobes at the base and a flat to shallowly indented tip.  Young leaves are opposite with large, rounded teeth and distinct stalks.

• Henbit:  Cotyledons are round to thumb shaped, and 0.13-0.5” (0.3-1.3 cm) long by 0.1-0.2” (0.25-0.5 cm) wide.  Seedling stems are purple.  The upper leaf surfaces and prominent veins on the underside of the leaf are coverd with fuzzy hairs.  Young leaves are round in outline, and have 2 to 4 teeth per side. 
• Purple deadnettle:  Cotyledons are oval shaped, red-stalked, hairless, and 0.47” (1.2 cm) long by 0.43” (1.1 cm) wide.   Fuzzy hairs are present on the blades and edges of young leaves.  Young leaves are round to broadly egg or heart-shaped, and have 2 to 4 teeth per side with one large lobe at the tip.

Mature plants have square, green to purple-tinged, weak stems that branch in a prostrate or leaning manner at the base with tips curving upright.  Leaves are opposite and heavily cross-veined, giving the surface a wrinkled appearance.  The distance between leaves shortens near stem tips, especially flowering tips.  The fibrous root system is shallow and supplemented by roots growing from stem-leaf junctions in contact with the ground. 

• Henbit:  Stems have downward pointing hairs and purple tinges; they can reach 4-16” (10-40 cm) tall.  Lower leaves are stalked and similar in appearance to seedling leaves.  Upper, stalk-less, fan shaped leaves encircle the stem almost completely.  Leaves are broadly round-toothed to lobed, softly hairy, strongly veined, round tipped, and 0.5-2” (1.3-5 cm) long (lower) or broad (upper).
• Purple deadnettle:  Stems are hairless to lightly hairy, streaked purple, and hollow; they can reach 4-20” (10-50 cm) tall.  Lower leaves are stalked and similar in appearance to seedling leaves.  Upper, small-stalked leaves are maroon, angle down to the ground, and do not encircle the stem.  Leaves are shallowly lobed, lightly hairy, pointy tipped, and 0.4-0.5” (1-1.3 cm) long.

Flowers are whorled in circles set just above upper leaf pairs. 

• Henbit:  Six to ten pink to dark purple flowers are present per leaf pair.  Flowers near stem tips are 0.5-0.75” (1.3-1.9 cm) long, with lightly hairy petals fused into a flared tube.  Flowers on lower whorls never fully open; they are small, inconspicuous, and self-pollinating.
• Purple deadnettle:  Three to six flowers are present per leaf pair.  Flowers have 0.5-0.7” (1.3-1.8 cm) long, fused, petals that are partially wrapped by green structures and hidden from view by leaf pairs.

Fruit and seeds:  Four brown, egg or thumb shaped, 0.06” (0.15 cm) long nut-like seeds are produced per flower.  Nutlets have two flat sides, one round side, and white spots.

• Henbit:  Nutlets are long and tapered to a flat tip.
• Purple deadnettle:  Nutlets are bumpy, broader, and rounder than henbit nutlets.

Similar species:  Young Persian speedwell (Veronica persica Poir.) has similar leaves, but is distinguishable by its round stems and blue or white flowers.  Ground ivy (Glechoma hederacea L.) also has blue flowers and long stalked, triangularly toothed, shiny surfaced leaves.  Ground ivy, however, is a strongly aromatic, mat-forming perennial with creeping stems.  Spotted deadnettle (Lamium maculatum L.) has white spots on the leaves and healall (Prunella vulgaris L.) has larger, round tipped, largely untoothed, egg or lance shaped leaves.

Management

Tillage in late fall is effective for killing purple deadnettle and fall emerging henbit to prevent seed production the next spring.  Unfortunately, soils are often too wet for tillage that time of year, and fall tillage leaves soil exposed to winter erosion.  Flame weeding is an effective alternative.  If the stand is dense, reduce ground speed to insure that sufficient heat reaches the base of the plant.  In areas where spring germinating henbit is a problem, tillage for late spring planted crops will destroy mid- to late-emerging cohorts, but early emerging plants may already have set seed.  Thus, tillage or flame weeding in late April may be necessary in addition to tillage in May.  In vegetable systems, an early planted crop of transplanted lettuce may become weedy with spring henbit, but the tillage before and after planting can be effective for breaking the weed's life cycle.

Cultivation of cool season vegetable crops to control henbit and purple deadnettle will be more successful if these weeds are small.  The spreading, fibrous root system of plants with several nodes holds soil well, and in cool weather the plants are slow to dry and can easily reroot.  They are especially difficult to kill after stems begin to root at the nodes.  For controlling purple deadnettle and fall emerging henbit in winter grains, till and plant midway in the planting window to allow a large proportion of seedlings to emerge first but still produce a competitive crop.  Seed at a heavy rate to allow aggressive tine weeding after crop establishment, and try to rotary hoe or tine weed before crop emergence as well.  Plant spring grains as early as possible to get the crop established before peak henbit emergence (Blackshaw and Brandt 2002).  Weed as for the winter grains.  If planting of spring grains has to be delayed, consider planting a later crop species instead so that tillage will kill off the henbit after it emerges.

Management of winter cover crops is critical for effective long-term control of both species in a vegetable rotation.  If fall rye or forage radish cover crops establish quickly and produce a high amount of ground cover, then henbit and purple deadnettle will be severely suppressed (Haramoto 2019, Lawley et al. 2011).  However, fall cover crops that do not establish well and leave significant gaps in the leaf canopy will allow either of these weeds to establish and set seed before cover crop termination in spring.  One alternative is to shift to an earlier planted cover crop of a winter hardy clover.  Use buckwheat as a nurse crop so that the clover does not become weedy with summer annuals, and mow it before seeds form.  The lack of late summer/fall tillage and the low light under the clover will reduce henbit and purple deadnettle emergence, and the clover will compete strongly with plants that do emerge.  Use a high clover seeding rate to ensure a dense, competitive stand.  In regions with hot, sunny summers, solarization can effectively destroy the surface henbit seed bank to prepare the soil for fall crops (Horowitz et al. 1982, Stevens et al. 1989).

Purple deadnettle is particularly adapted to the moist, protected soil environment of fields with incomplete crop residue cover left untilled over winter (J. Teasdale, personal observation).  However, complete ground cover by wheat straw reduced henbit density by 77% relative to a no-straw control following minimum tillage and completely suppressed henbit in an organic no-till crop of winter fava bean (Bilalis 2003).

Ecology

Origin and distribution:  Both species are native to the Mediterranean region of Eurasia and North Africa (Defelice 2005).  Henbit has spread throughout Europe and much of Asia and been introduced into Australia, New Zealand, North America, and temperate and mountainous parts of South America (Holm et al. 1997).  It occurs throughout the U.S.A. and southern Canada (USDA Plants).  Purple deadnettle is now a weed across most of Europe, North America, and New Zealand (Defelice, 2005).  It is most common in the eastern half of the U.S.A. and along the Pacific Coast, including Alaska.  It occurs only sporadically in the High Plains and Intermountain West (USDA Plants).

Seed weight:  Henbit, 0.5-0.6 mg (EFBI); purple dead nettle, 0.70 mg (EFBI), 0.65-0.92 mg (Klisarišić et al. 2006), 0.8 mg (Storkey et al. 2010).

Dormancy and germination:  Henbit seeds are dormant when shed from the parent plant.  After exposure to high summer temperatures for several weeks, seeds from Kentucky populations germinated well at any temperature regimen from a constant 41 °F to a 86/68 °F day/night regime (5 °C to 30/20 °C).  Both dormant seeds and seeds that have lost dormancy through warm summer temperatures become conditionally dormant during exposure to winter temperatures (e.g., 41 °F or 5 °C), and then will only germinate at temperatures below 68/50 °F (20/10 °C).  Consequently, seeds germinate in hot weather in the late summer, or cool weather in the fall or early spring, but not in the warm weather of late spring or summer.  This ensures that the plants will have time to grow during cool seasons of the year (Basking and Baskin 1981, 1984a, Baskin et al. 1986).  In the cold climate of Sweden, dormancy was broken by a long (24 week) period of warm, dry conditions, and emergence in the field occurred almost entirely in the spring (Karlsson and Milberg 2008).  Another study showed that non-dormant seeds of henbit germinated best at 68 °F (20 °C) (Blackshaw and Brandt 2002). 

Purple deadnettle seeds are also dormant when shed in the spring.  Hot summer temperatures break dormancy of seeds from Kentucky by late spring or early summer, but germination is inhibited by hot summer day/night temperatures of 86/59 °F (30/15 °C) or higher.  When temperatures cool in the fall to 68/50 °F (20/10 °C) or lower, the seeds can then germinate.  A few weeks of cold winter temperatures (e.g., 41 °F or 5 °C) induce a secondary dormancy so that the seeds will not germinate in the same mild temperatures in the spring that allowed germination in the fall. This secondary dormancy is again broken by hot temperatures in late spring or early summer and the cycle repeats.  This dormancy cycle causes purple deadnettle to act as a strict winter annual, at least in the central U.S.A. (Baskin and Baskin 1984b, Baskin et al. 1986).  In Sweden, warm moist or dry conditions break dormancy as in the central U.S.A.  However, most emergence occurs in the spring, implying that cold temperatures during the winter do not induce dormancy.  In Sweden, seedlings emerging in the fall often die without reproducing (Karlsson and Milbeerg 2008).  Dormancy cycles in the northern U.S.A. and Canada require study.

Germination of non-dormant seeds of both species is generally stimulated by light (Baskin and Baskin 1988, Karlsson and Milberg 2008), although one study found that light inhibited germination of henbit (Jones and Bailey 1956).

Seed longevity:  Viable seeds of both species have been found beneath medieval ruins in Europe (Ødum 1965).  In a more typical agricultural setting, 20-50% of henbit seeds survived 20 years under sod (Chancellor 1986).  Purple deadnettle seeds in annually tilled winter wheat and oil seed crops declined by 39 and 60 % per year (Wilson and Lawson 1992).  In another experiment, purple deadnettle seed density declined at an average of only 20% per year, with the decline faster in spring wheat than in winter wheat (Lutman et al. 2002).  Average seed loss over a five-year period from soil stirred three times per year was 43-60% per year for henbit and 43-53% per year for purple dead nettle (calculated from Roberts and Bodrell 1983).

Season of emergence:  Henbit emerges in mid-spring and in early autumn but emergence is primarily in autumn in the South and primarily in spring in the prairie provinces of Canada (Baskin et al. 1986, Baskin and Baskin 1988, Blackshaw and Brandt 2002, Roberts and Bodrell 1983, Woolam et al. 2018).  In Michigan, emergence occurs spring to fall with peak emergence in late summer (Hill et al. 2014).  Purple deadnettle emerges only in autumn in Kentucky (Baskin et al. 1986), but throughout the growing season with a peak in autumn in England (Roberts and Bodrell 1983) and primarily in the spring in Sweden (Karlsson and Milberg 2008). 

Emergence depth:  Most seedlings of henbit and purple deadnettle emerge from the top 1” (2.5 cm) of soil, though a few can emerge from as deep as 2.5” (6.3 cm) (MSU Weed Science).   

Photosynthetic pathway:  C3

Sensitivity to frost:  Both species are frost tolerant.  Henbit can tolerate temperatures down to 18 °F (-8 °C) but suffers some damage at that temperature (Cici and Van Acker, 2011).  Fall emerging plants of both species can overwinter in the northern U.S.A. (MSU Weed Science, Mohler personal observation), but snow cover likely improves survival.

Drought tolerance:  Henbit is drought-intolerant (Baskin and Baskin, 1984a).

Mycorrhiza:  Both species are mycorrhizal (Harley and Harley 1987).

Response to fertility:  Henbit response to N was intermediate among 24 weeds and crops studied and was roughly similar to wheat (Blackshaw et al. 2003).  Of the same 24 species, it was among the group of species most responsive to P fertility (Blackshaw et al. 2004).  In another experiment, however, four years of manure or compost either with or without additional sulphate of ammonia had negligible effects on late spring henbit density in vegetable crops (Mann 1957).  Eight years application of various N fertilizers decreased henbit relative to plots that received no N, probably because increased vigor of fertilized winter grains suppressed the low growing henbit (Pyšek and Lepš 1991).  On a sandy soil, henbit was insensitive to pH from 5.0 to around 7.0, but below pH 5.0 density decreased although its proportion of the weeds present increased (Mann 1957). 

Soil physical requirements:  Henbit is often found in light, sandy soils but occurs on a range of rich agricultural soils (Defelice 2005, Holm 1997).  Purple deadnettle is usually found in rich, loamy or sandy-loam soils (Allan 1978).

Response to shade:  Henbit is shade-intolerant (Baskin & Baskin 1984a).  Purple deadnettle partially avoids shade through increased stem elongation in environments with competition from other plants (Klisarišić 2006).

Sensitivity to disturbance:  Fragments of purple deadnettle re-root readily after shallow tillage or hoeing (Mohler personal observation).   

Time from emergence to reproduction:  In warm climates, fall germinating henbit flowers in late winter to early spring (Petanidou and Vokou 1993).   In the northern U.S.A. and southern Canada, fall germinating plants flower from April to June (Hill et al. 2014, Muenscher 1980).  Spring germinating plants emerging in early April in Wisconsin began flowering 36 days later (Doll 2002), but some spring and summer emerging plants in the northern U.S.A. do not flower until September (Muenscher 1980).  Purple deadnettle flowers from late March/early April to mid-May in Ohio (Macior 1978).  A relatively short time is required for viable seed to be produced after flowering, because peak shedding of henbit seeds occurred in mid-May, within a month from when flowering began (Hill et al. 2014).

Pollination:  Henbit forms closed self-pollinating flowers on the lower nodes and sometimes the whole plant but often produces open, cross pollinated flowers at the upper nodes (Lord 1979).  Pollination is by solitary bees (Petanidou and Vokou 1993) and honeybees (Defelice 2005).  Purple deadnettle self-pollinates, but it is also pollinated by bumblebees and other bee species (Macior 1978). 

Reproduction:  A typical henbit plant produces between 200 and 2,000 seeds (Defelice 2005), but a particularly large plant produced 60,000 seeds (Holm 1997).  Purple deadnettle produced about 600 seeds per plant (Salisbury 1978), but can produce 27,000 seeds if grown without competition (MSU Weed Science).  Purple deadnettle spreads as a mat of stems that root at the nodes, and, if fragmented by tillage, rooted stem sections can re-establish (Mohler, personal observation).

Dispersal:  Both species form persistent seed banks and probably commonly disperse in soil clinging to farm machinery and the bodies of cattle.  Purple deadnettle seeds have been found in soil adhering to an automobile traveling in rural areas (Schmidt 1989) and also in commercial topsoil (Hodkinson and Thompson, 1997).  Seeds of both species have specialized bodies that provide a food source attractive to non-seed eating ants.  These presumably encourage dispersal by ants (Pemberton and Irving 1990).

Common natural enemies:  Both species are favored food sources for a variety of slug species (Kozłowski and Kozłowska 2003). 

Palatability:  These species are sometimes eaten as salad or pot herbs, particularly in Japan (Defelice 2005).  Henbit has digestibility, crude protein and mineral content similar or higher than common forage grasses (Bosworth et al. 1985).  Grazing on henbit can cause mild neurological problems in sheep, cattle, and horses but the condition is rare and reversible.  Purple deadnettle has no reported toxic properties for ruminants (Defelice 2005).

References

• Allan M.  1978.  Weeds: The Unbidden Guests in our Gardens.  Viking: New York.
• Baskin, J. M., and C. C. Baskin.  1981.  Seasonal changes in the germination responses of buried Lamium amplexicaule seeds.  Weed Research 21:299-306.
• Baskin, J. M., and C. C. Baskin.  1984a.  Effect of temperature during burial on dormant and non-dormant seeds of Lamium amplexicaule L. and ecological implications.  Weed Research 24:333-339. 
• Baskin, J. M., and C. C. Baskin.  1984b.  Role of temperature in regulating timing of germination of soil reserves of Lamium purpureum L.  Weed Research 24:341-349.
• Baskin, C. C., and J. M.. Baskin.  1988.  Germination ecophysiology of herbaceous plant species in a temperate region.  American Journal of Botany: 75:286-305.
• Baskin, J. M., C. C. Baskin, and J. C. Parr.  1986.  Field emergence of Lamium amplexicaule L. and L. purpureum L. in relation to the annual seed dormancy cycle.  Weed Research 26:185-190.
• Bilalis, D., N. Sidiras, G. Economou, and C. Vakali.  2003.  Effect of different levels of wheat straw soil surface coverage on weed flora in Vica faba crops.  Agronomy and Crop Science 189:233-241.
• Blackshaw, R. E., and R. N. Brandt.  2002.  Soil temperature and soil water effects on henbit emergence.  Weed Science 50:494-497.
• Blackshaw, R. E., R. N. Brandt, H. H. Janzen, T. Entz, C. A. Grant, and D. A. Derksen. 2003.  Differential response of weed species to added nitrogen.  Weed Science 51:532-539.
• Blackshaw, R. E., R. N. Brandt, H. H. Janzen, and T. Entz.  2004.  Weed species response to phosphorus fertilization.  Weed Science 52:406-412.
• Bosworth, S. C., C. S. Hoveland, and G. A. Buchanan.  1985.  Forage quality of selected cool-season weed species.  Weed Science 34:150-154.
• Chancellor, R. J.  1986.  Decline of arabelweed seeds during 20 years in soil under grass and the periodicity of emergence after cultivation.  Journal of Applied Ecology 23:631-637.
• Cici, S. Z. H., and R. C. Van Acker.  2011.  Relative freezing tolerance of facultative winter annual weeds.  Canadian Journal of Plant Science 91:759-763.
• Defelice, M. S.  2005.  Henbit and the deadnettles, Lamium spp.--archangels or demons? Weed Technology 19:768-774
• Doll, J.  2002.  Know when to look for what: weed emergence and flowering sequences in Wisconsin.  University of Wisconsin, Weed Science.  https://extension.soils.wisc.edu/wp-content/uploads/sites/68/2016/07/Doll-2.pdf
• EFBI.  Ecological Flora of the British Isles.  http://www.ecoflora.co.uk/
• Hill, E. C., K. A. Renner, and C. L. Sprague.  2014.  Henbit (Lamium amplexicaule), common chickweed (Stellaria media), shepherd's purse (Capsella bursa-pastoris), and field pennycress (Thlaspi arvense): fecundity, seed dispersal, dormancy, and emergence.  Weed Science 62:97-106.
• Hodkinson, D. J., and K. Thompson.  1997.  Plant dispersal: the role of man.  Journal of Applied Ecology 34:1484-1496.
• Holm, L., J. Doll, E. Holm, J. Pancho, and J. Herberger.  1997.  World Weeds: Natural Histories and Distribution.  Wiley: New York.
• Haramoto, E. R.  2019.  Species, seeding rate, and planting method influence cover crop services prior to soybean.  Agronomy Journal 111:1068–1078.
• Harley, J. L., and E. L. Harley.  1987.  A check‐list of mycorrhiza in the British flora.  New Phytologist 105:1-102.
• Horowitz, M., Y. Regev, and G. Herzlinger.  1982.  Solarization for weed control.  Weed Science 31:170-179.
• Jones, M. B., and L. F. Bailey.  1956.  Light effects on the germination of seeds of henbit (Lamium amplexicaule L.).  Plant Physiology 31:347-349
• Karlsson, L.M., and P. Milberg.  2008.  Variation within species and inter-species comparison of seed dormancy and germination of four annual Lamium species.  Flora 203:409-420.
• Klisarišić, N. B., B. Stojković, and A. Tarasjev.  2006.  Genetic differences between populations and habitats in Lamium purpureum plastic response to conspecific density.  Russian Journal of Genetics 42:165-171.
• Kozłowski, J., and M. Kozłowska.  2003.  Evaluation of food preferences and tolerance of slugs Deroceras reticulatum, Arion lusitanicus and Arion rufus (I Group of Plants) with references to various herbs.  Journal of Plant Protection Research 43:382-390.
• Lawley, Y. E., R. R. Weil, and J. R. Teasdale.  2011.  Forage radish cover crop suppresses winter annual weeds in fall and before corn planting.  Agronomy Journal 103:137-144.
• Lord, E.  1979.  The development of cleistogamous and chasmogamous flowers in Lamium amplexicaule (Labiatae): an example of heteroblastic inflorescence development.  Botanical Gazette 140:39-50.
• Lutman, P. J. W., G. W. Cussans, K. J. Wright, B. J. Wilson, G. M. Wright, and H. M. Lawson.  2002.  The persistence of seeds of 16 weed species over six years in two arable fields.  Weed Research 42:231-242.
• Macior, L. W.  1978.  Pollination interactions in sympatric Dicentra species.  American Journal of Botany 65:57-62.
• Mann, H. H.  1957.  Weed herbage of slightly acid arable soils as affected by manuring.  Journal of Ecology 45:149-56.
• MSU Weed Science.  Michigan State University, Department of Crop and Soil Science, Michigan’s Worst Weeds.  https://www.canr.msu.edu/weeds/extension/michigan-s-worst-weeds
• Muenscher, W. C.  1980.  Weeds, Second Edition.  Cornell University Press: Ithaca, NY.
• Ødum, S.  1965.  Germination of ancient seeds: floristical observations and experiments with archaeologically dated soil samples.  Dansk Botanisk Arkiv 24:3-70.
• Pemberton, R. W., and D. W. Irving.  1990.  Elaiosomes on weed seeds and the potential for myrmecochory in naturalized plants.  Weed Science 38:615-619.
• Petanidou, T., and D. Vokou.  1993.  Pollination ecology of Labiatae in a phryganic (East Mediterranean) ecosystem.  American Journal of Botany 80:892-899.
• Pyšek, P., and J. Lepš.  1991.  Response of a weed community to nitrogen fertilization: a multivariate analysis.  Journal of Vegetation Science 2:237-44.
• Roberts, H. A., and J. E. Bodrell.  1983.  Seed survival and periodicity of seedling emergence in ten species of annual weeds.  Annales of Applied Biology 102:523-532.
• Salisbury, E.  1978.  A note on seed production and frequency.  Proceedings of the Royal Society of London. Series B, Biological Sciences 200:485-487.
• Schmidt, W.  1989.  Plant dispersal by motor cars.  Vegetatio 80:147-152.
• Stevens, C., V. A. Khan, A. Y. Tang, C. Bonsi, and M. Wilson.  1989.  Long-term effects of solarization on controlling weeds and root-knot nematodes.  HortScience 24:762.
• Storkey, J., S. R. Moss, and J. W. Cussans.  2010.  Using assembly theory to explain changes in a weed flora response to agricultural intensification.  Weed Science 58:39-46.
• USDA Plants Database.  United States Department of Agriculture, Natural Resources Conservation Service.  http://plants.usda.gov/
• Wilson, B. J., and H. M. Lawson.  1992.  Seedbank persistence and seedling emergence of seven weed species in autumn-sown crops following a single year’s seeding.  Annals of Applied Biology 120:105-116.
• Woolam, B. C., D. O. Stephenson, IV, and D. C. Blouin.  2018.  Determining seasonal emergence and control programs for henbit (Lamium amplexicaule L.).  Weed Technology 32:733-738.