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How to Manage PestsPests in Gardens and Landscapes
Spotted spurge, Euphorbia (=Chamaesyce) maculata, is an annual species that is native to the eastern United States. It is common throughout California and has become a serious weed in many crops including citrus, turf, ornamental beds, and container ornamentals. IDENTIFICATIONSpotted spurge is a low-growing annual plant that often forms a dense mat. It has dark green, opposite leaves that are 1/8 to 1/2-inch long and about 1/8-inch wide. Leaves are usually marked with a red spot midway down the center leaf vein. Each leaf has a short stem (petiole) with a separate stipule, or little scalelike appendage at its base; you may need a 10X hand lens to see the stipule. The stem, when broken, exudes a milky latex juice. The plant has a central taproot system that is capable of extending more than 2 feet into the soil. The tiny, pinkish flowers consist of only stamens and pistils and are grouped in small flowerlike cups (cyathia) in the leaf axils. The fruit is a three-celled seed capsule that is 1/16-inch long or less. Each cell contains one seed that is about 1/25-inch long. Although spotted spurge is the major spurge weed in California, there are six other species of spurges that appear regularly as weeds in the state: garden spurge (E. hirta); nodding spurge (E. nutans); ground spurge (E. prostrata); creeping spurge (E. serpens); petty spurge (E. peplus); and thyme-leafed spurge (E. serpyllifolia). Ground spurge and creeping spurge are both widespread and troublesome weeds in California; petty spurge is a problem in southern California landscapes; and garden spurge, nodding spurge, and thyme-leafed spurge are much less frequently the source of problems. In addition to these weed species there are 17 native species of spurge that occur in arid plant communities. A few individuals of some of these native species may appear at the margins of cultivated areas adjacent to wildlands, but they are poorly adapted to cultivated conditions and rarely occur as weeds. The plant key in this Pest Note (Table 1) is provided to identify all the spurges commonly encountered as weeds in California. Any weedy spurge that does not appear to fit the characteristics described in this key may be keyed using The Jepson Manual, listed in "References," or may be pressed and sent to the third author (Andy Sanders, Herbarium Curator, Botany and Plant Sciences, University of California, Riverside, CA 92521) for identification. Unidentifiable plants may be either native species not treated here or newly introduced weeds such as garden spurge, which has only very recently been detected in the state.
IMPACTSpotted spurge can become established in horticultural, agricultural, and noncrop sites. It overgrows turf and low-growing ground covers; invades open areas in gardens and landscapes; and can grow in sidewalk cracks. Spotted spurge is often found in citrus groves where it is tolerant of the herbicides commonly used for weed control in citrus. In addition to reducing the growth of desirable species, spotted spurge reduces uniformity and quality of turf, provides habitat for undesirable insects in citrus, serves as an intermediate host for fungal diseases of cultivated crops, and attracts ants with its seed. Spotted spurge is poisonous and has been known to cause death when sheep graze pastures where it is the predominant weed. Sheep that consumed as little as 0.62% of their body weight of spotted spurge have died within a few hours. BIOLOGYSpotted spurge is a summer annual that does not like competition and depends on its prolific seed production for survival. A single plant is capable of producing several thousand seeds. Seeds are small and can remain dormant in the soil until conditions are suitable for germination. Seeds that are produced in summer germinate readily whereas those produced in late fall are mostly dormant and won’t germinate until spring. Spotted spurge germinates best when temperatures are between 75° and 85°F, but germination can occur at temperatures as low as 60°F and as high as 100°F. Thus, when moisture is available, germination can occur from February through September in most areas of California. Light is also required for maximum germination; seeds buried deeper than 1/2 inch will not germinate well. Plants that germinate early in spring under cool conditions may remain as small seedlings until temperatures are more desirable for growth. Once the seed germinates, a small rosette of leaves develops. As growth continues, the leaves form a dense mat that can grow up to 3 feet in diameter. Reproductive growth is rapid and seeds can be produced as soon as 5 weeks after germination. MANAGEMENTThe primary method of managing spotted spurge should be prevention—it is very difficult to control this weed once it is established. Avoid bringing spotted spurge seeds into uninfested areas: use weed-free planting seed and uncontaminated planting stock. Clean machinery (lawn mowers) and workers' clothing to remove any weed seeds that might be present. Infested areas must be constantly monitored to cultivate or hand-pull new plants before they produce seed. Plants that are hand-pulled often break at the stem, leaving the root and several buds or a single stem from which regrowth is possible. Germination can be reduced if it is possible to bury the seeds or add a layer of mulch to cover them. When mulching, put at least 1 inch of a fine mulch or 3 inches of a coarse mulch (bark, etc.) on the soil surface. Be careful that seeds do not get on top of the mulch or they will germinate and grow there. Before planting areas to turf or ornamentals, soil solarization (covering the soil with sheets of clear plastic for 5 to 6 weeks during the summer) may be an effective method of reducing the viable seed population in areas where summer temperatures are hot (90°F or higher). TurfOne of the best control measures for spotted spurge in turf is to maintain a competitive stand of grass. Where open areas develop in the turf either from stress, disease, insects, or abuse, light is able to penetrate to the soil surface, allowing spotted spurge to germinate. Once spotted spurge is established, altering cultural practices (mowing height, fertilization or irrigation) will not control it, but raising the mowing height in tall fescue or perennial ryegrass to 2 inches or more may reduce initial invasions. Preemergent herbicides are helpful in reducing establishment of spotted spurge if they are applied in late winter before weed seeds germinate. Check the soil temperature to make sure the herbicides are applied before soil temperature at 1 inch exceeds 55° to 60°F. Preemergent herbicides for spurge in turf include pendimethalin (Pendulum), isoxaben (Gallery), DCPA (Dacthal), oxadiazon (Ronstar), and dithiopyr (Dimension); of these herbicides, only pendimethalin, dithiopyr, and isoxaben are available for use by the home gardener. Combination products are also available for both the home gardener and professional landscaper; examples include trifluralin plus benefin and oryzalin plus benefin. Two postemergent contact herbicides, bromoxynil (available for commercial use only) and glufosinate (available for both commercial and home landscape use), can be applied to spotted spurge plants to reduce populations. Container-Grown Ornamentals and Ornamental BedsHand-pull spotted spurge plants from containers or ornamental beds. There are no selective herbicides that will control spurge once it is established. If planting new containers, be sure to use sterilized or weed-free planting mix. When purchasing container plants or stock for ornamental beds, avoid those with spotted spurge infestations. Preemergent herbicides will control spotted spurge if applied before emergence of the weed. These herbicides include pendimethalin, oryzalin, oxadiazon, prodiamine, and isoxaben (only oryzalin is available for home garden use). Combinations of herbicides are also available: oryzalin plus benefin, which can be used on ornamental beds but not for container-grown plants by both the home gardener and professional landscaper, and isoxaben plus trifluralin, which is available for professional use only. Mulches can effectively limit spotted spurge if they prevent light from reaching the seed. Hand-pull seedlings that escape preemergent herbicide treatment or germinate on the surface of mulches before they mature and produce seed. CitrusSpotted spurge is not controlled by the preemergent herbicides commonly used in commercial citrus orchards. It grows around drip emitters and low volume emitters and provides a habitat for insects that clog the emitters. Cultivation is not a viable option for control in citrus as it disturbs the shallow root system of the citrus, but a shallow scraping of the soil with a shuffle hoe may provide control. Spot treatments with the postemergent herbicide glyphosate can remove infestations, but retreatment is usually necessary every 6 to 8 weeks during the growing season. Preemergent treatment with oryzalin is helpful if it is applied in late winter before spotted spurge seeds germinate. WARNING ON THE USE OF CHEMICALS REFERENCESDerr, J. F. 1994. Weed control in container-grown herbaceous perennials. Hort. Sci. 29 (2):95-97. Elmore, C. L., J. J. Stapleton, C. E. Bell, and J. E. DeVay. 1997. Soil Solarization: A Nonpesticidal Method for Controlling Diseases, Nematodes, and Weeds. Oakland: Univ. Calif. Agric. Nat. Res. Leaflet 21377. Elmore, C. L., and J. A. Roncorni. 1986. Postemergent control of Euphorbia maculata (spotted spurge). West. Soc. Weed Sci. Res. Prog. Rep. p. 84. Koutnik, D. L. 1993. Chamaesyce. In J. C. Hickman, ed. The Jepson Manual: Higher Plants of California. Berkeley: Univ. Calif. Press. Krueger, R. R., and D. L. Shaner. 1982. Germination and establishment of spotted spurge (Euphorbia supina). Weed Sci. 30:286-290. Whitson, T. D. et al. 1996. Weeds of the West. Jackson: Univ. Wyoming. 630 pp. PUBLICATION INFORMATION![[UC Peer Reviewed]](/IMAGES/logo-ucpeerreviewed.jpg){kind=logo}
Pest Notes: Spotted Spurge Authors: D. W. Cudney, Botany and Plant Science, UC Davis; C. L. Elmore,
Vegetable Crops/Weed Science; and A. Sanders. Send samples to Andy Sanders, Herbarium Curator, Botany and Plant Sciences,
University of California, Riverside, CA 92521. PDF: You need a PDF reader, such as Acrobat Reader version 8 or later, to view or print this PDF. If no reader is installed on your computer, you can download a free copy of Adobe Acrobat Reader. |
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