BURNING & STINGING NETTLES

Integrated Pest Management for Home Gardeners and Landscape Professionals

Burning nettle (Urtica urens) and sting- ing nettle does not generally occur ing nettle (Urtica dioica) belong to the in the desert and areas above 9800 family Urticaceae. Both are upright feet. The species commonly infests plants, which are well recognized for moist uncultivated areas including their stinging hairs. Although both waste places, riverbanks, fence rows are often called stinging nettle, that and roadsides, and is occasionally a common name only applies to Urtica problem in orchards and vineyards. It dioica. Despite their similarity in caus- is not generally a problem in gardens ing skin irritation, the two species are and row crops. considerably different in their biology and preferred habitat. IDENTIFICATION Burning Nettle. Burning nettle is a Figure 1a. Seedling of burning nettle Burning nettle, Urtica urens, is also small to medium-size summer annual viewed from above showing rounded known as dwarf nettle or small nettle. broadleaf weed common in gardens. cotyledons (seed leaves) and serrated It is native to Europe, but in the United The first new seed leaves, or cotyle- first true leaves. States is common in many eastern dons, are bright green, notched at the states and a few central states. It also tips, but smooth along the edges. The occurs in the western United States, first true leaves have serrated margins, including Arizona, California, Ne- and occur opposite each other on the vada, New Mexico, Oregon, Texas, and stalk (Fig. 1a). The leaf blade and the Washington. In California, burning stalk have both stinging and non- nettle is widely distributed, although stinging hairs. Mature plants can be 5 it is not known to occur in the des- inches to 2 feet tall. Plants are slender ert, the Klamath Mountain range or and upright with sparse, four-angled in the higher regions of the Cascade stems. Stinging hairs on stems and flower cluster Mountain range above 9800 feet. It is leaves are long. Shorter nonstinging especially common along the Califor- hairs may also be present. The two nia coast. Burning nettle commonly opposite, stalked leaves have toothed infests disturbed sites, such as fence margins and are 1/2 to 2 inches long rows, ditch banks and roadsides, but with 3 to 5 veins radiating from the can also be a problematic weed in base. Flowers are about 2/5 of an inch gardens, vegetable crops, sugar beets, long and greenish white. The plant Figure 1b. Flowering stem of burning citrus and deciduous orchards. contains both male and female flowers nettle, showing headlike clusters of flowers. that occur in the same cluster (Fig. 1 b). 1 1 Stinging nettle, Urtica dioica, is native Fruits are small ( /16 to /10 of an inch), stinging hairs as well as nonstinging to North America, including Califor- triangular, with one seed. hairs. Full grown plants can be 3 1/2 nia and other Western U. S. states. This to 10 feet tall, but can reach 20 feet in species has two widespread, subspe- Stinging Nettle. Stinging nettle is a tall some situations. Stems are angular, cies that include the subspecies graci- perennial broadleaf weed that often often branched from the base and have lis, commonly known as American grows in colonies. The cotyledons long stinging hairs as well as short, stinging nettle, California nettle, coast (seed leaves) are round to oval, and nonstinging hairs. Leaves are oppo- nettle, or Lyall nettle, and the subspe- hairless except for a few stinging hairs site and 2 1/2 to 5 inches long with 3 to cies holosericea, known as California and sparse, short, nonstinging hairs. 5 veins radiating from the base and slender nettle, creek nettle, giant creek The first true leaves have margins that coarsely toothed and lance shaped. nettle, hedge nettle, hoary nettle, or are coarsely round-toothed on short Separate male and female flower clus- mountain nettle. In California, sting- stalks. Leaf surfaces are coated with ters occur at the base of the leafstalks

PEST NOTES Publication 74146 University of California Agriculture and Natural Resources October 2008 October 2008 Burning & Stinging Nettles

and are whitish green and inconspicu- choline and histamine. Unlike poison ous (Fig. 2). Fruits are small (1/25 of an oak, which causes a red, itchy, weepy inch) and egg shaped. reaction called allergic dermatitis in only a portion of the population, the LIFE CYCLE nettles affect everyone equally. This is Burning Nettle. Burning nettle seeds known as irritant dermatitis. germinate from late fall through early spring. Plants may produce viable Along the coast, burning nettle is par- seeds within five weeks of germina- ticularly problematic because it grows tion. Flowers generally bloom from year-round. Stinging nettle plants can January to April, but blooms can be become a nuisance for farmers when flowers seen year-round in milder climates such as along the California coast. As large stands block irrigation water- an annual plant, it dies within one ways. Stinging nettle prefers moist year. areas in wildlands, such as areas surrounding creeks or rivers. If these Figure 2. Flowering stem of stinging Stinging Nettle. Stinging nettle seeds sites occur along hiking trails, plants nettle, showing flowers on longer germinate in the spring. Underground can be a nuisance or even a health panicles. stems, or rhizome fragments, can hazard to visitors. also develop into mature plants un- der favorable conditions. Often large MANAGEMENT clumps of plants grow from rhizomes Burning and stinging nettles growing REFERENCES in uncultivated areas. The flowers in the home garden and landscape DiTomaso, J. M., and Healy, E. M. 2007. Weeds of California and other Western bloom from March to September. As are best controlled using cultural and States. Oakland: Univ. Calif. Agric. Nat. a perennial plant, stinging nettle may mechanical methods. live for several years regrowing from Res. Publ. 3488. rhizomes. Cultural and Mechanical Fischer, W. 1998. Grower’s Weed Identi- Control fication Handbook. Oakland: Univ. Calif. IMPACT Burning and stinging nettles can be Both burning and stinging nettle are Agric. Nat. Res. Publ. 4030. controlled by removing plants by aptly named. Their leaves and stems hand. However, it is important to are covered with long, fine to bris- Kulze, A. and Greaves, M. 1988. tly hairs that can irritate and blister wear gloves to protect skin from the Contact urticaria caused by stinging skin when handled. When human stinging hairs. For stinging nettle, nettles. British Journal of Dermatology. skin comes into contact with a leaf or ensure that the underground portion 119, 269-270. stem, it often rapidly develops red- called rhizomes are removed or the dish patches accompanied by itching plants will regrow. Because stinging Whitson, T. D., L. C. Burrill, S. A. and burning. Frequently, a prolonged nettles are native to California and Dewey, D. W. Cudney, B. E. Nelson, R. the western United States, control D. Lee, and R. Parker. 2002. Weeds of the tingling sensation may persist on the ❖ affected skin for more than 12 hours, should only be performed in areas West. Jackson, Wyo.: Univ. Wyoming. even after visible symptoms have where they cause economic or health faded. problems. Close mowing can prevent the development of fruit. Be aware The prickly hairs of both burning and that cultivating the soil may spread stinging nettle consist of a minute the rhizomes of stinging nettle, thus tubelike structure that has a hard increasing the size of the population. round bulb at the tip and a softer ves- Repeated cultivation works best as a sel at the base. This bulb breaks off control for this weed. after contact with skin and exposes a needlelike point. When the tip con- tacts and penetrates the skin, it puts Chemical Control pressure on the basal vessel and Herbicides listed to control burning results in the needlelike injection of and stinging nettles include isoxa- irritating substances under the skin. ben, oxadiazon and oxyfluorfen, but The contents of the structures are not these materials are available only to fully known, but have been found to licensed pesticide applicators. Refer contain active concentrations of the to the herbicide label for proper use of neurotransmitter chemicals acetyl- these products.

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For more information contact the University of California Cooperative Extension in your county. See your telephone directory for addresses and phone numbers.

AUTHORS: A. E. Schellman, UCCE Stan- islaus County, A. Shrestha, UC Statewide IPM Program, Kearny Agricultural Center, Parlier TECHNICAL EDITOR: M. L. Flint COORDINATION & PRODUCTION: P. N. Galin WARNING ON THE USE OF CHEMICALS ILLUSTRATIONS: Figs. 1, 2: W. Suckow Pesticides are poisonous. Always read and carefully follow all precautions and safety recommendations given on the container label. Store all chemicals in the original labeled containers in a locked cabinet or shed, Produced by UC Statewide IPM Program, away from food or feeds, and out of the reach of children, unauthorized persons, pets, and livestock. Pesticides applied in your home and landscape can move and contaminate creeks, rivers, and oceans. University of California, Davis, CA 95616 Confine chemicals to the property being treated. Avoid drift onto neighboring properties, especially gardens containing fruits or vegetables ready to be picked. This Pest Note is available on the Do not place containers containing pesticide in the trash or pour pesticides down sink or toilet. Either use World Wide Web (www.ipm.ucdavis.edu) the pesticide according to the label or take unwanted pesticides to a Household Hazardous Waste Collection site. Contact your county agricultural commissioner for additional information on safe container disposal and for the location of the Household Hazardous Waste Collection site nearest you. Dispose of empty containers by following label directions. Never reuse or burn the containers or dispose of them in such a manner that they may contaminate water supplies or natural waterways. The University of California prohibits discrimination or harassment of any person on the basis of race, color, national origin, religion, sex, gender identity, pregnancy (including childbirth, and This publication has been anonymously peer medical conditions related to pregnancy or childbirth), physical or mental disability, medical condition reviewed for technical accuracy by University of (cancer-related or genetic characteristics), ancestry, marital status, age, sexual orientation, citizen- California scientists and other qualified profession- ship, or service in the uniformed services (as defined by the Uniformed Services Employment and als. This review process was managed by the ANR Reemployment Rights Act of 1994: service in the uniformed services includes membership, applica- Associate Editor for Urban Pest Management. tion for membership, performance of service, application for service, or obligation for service in the To simplify information, trade names of products uniformed services) in any of its programs or activities. University policy also prohibits reprisal or have been used. No endorsement of named products retaliation against any person in any of its programs or activities for making a complaint of discrimi- is intended, nor is criticism implied of similar products nation or sexual harassment or for using or participating in the investigation or resolution process of that are not mentioned. any such complaint. University policy is intended to be consistent with the provisions of applicable This material is partially based upon work supported State and Federal laws. Inquiries regarding the University’s nondiscrimination policies may be di- by the Extension Service, U.S. Department of rected to the Affirmative Action/Equal Opportunity Director, University of California, Agriculture and Agriculture, under special project Section 3(d), Natural Resources, 1111 Franklin Street, 6th Floor, Oakland, CA 94607, (510) 987-0096. Integrated Pest Management.

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