Poverty sumpweed or Povertyweed [Iva axillaris Pursh. ssp. robustior (Hook.) Bassett][IVAAX][CDFA list: C] Photographs
SYNONYMS:povertyweed, small-flowered marsh elder, death-weed, devil’s-weed, salt sage, bozzleweed, Iva axillaris Pursh. ssp. pubescens A. Gray
GENERAL DESCRIPTION:Long-lived perennial with vigorous creeping roots, to 0.6 m tall. Poverty sumpweed is a widespread native of Western North America and a desirable component of salt marsh and alkali plains communities. However, it sometimes forms large clonal colonies on sites subjected to disturbances such as cultivation or overgrazing. Once established, colonies are difficult to eradicate. Studies suggest that plants have allelopathic properties. Colonies in cultivated fields can significantly reduce crop yields. Handling foliage may cause contact dermatitis and inhaling pollen can trigger allergic responses in sensitive individuals. Elsewhere it has been associated with selenium poisoning of livestock grazing on high selenium soils, but animals seldom consume the unpalatable foliage.
SEEDLINGS:No information available.
MATURE PLANT:Foliage has an unpleasant aromatic odor and is +/- glabrous to moderately covered with short stiff hairs. Stems +/- erect, bushy, mostly branched from a woody crown. Leaves opposite on lower portions of stems, +/- alternate near tips, narrowly elliptic to obovate, with rounded tips, 1-4 cm long, thick, leathery, +/- sessile, typically dotted with resinous red-tinged glands. Margins smooth.
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ROOTS and UNDERGROUND STRUCTURES:Roots creeping, woody, highly branched, slender, deep (to 2.5 m), with numerous shoot buds. Roots store abundant reserves and fragments produce new plants.
FLOWERS:May-September. Flower heads greenish, 5-7 mm wide, nodding on short stalks, solitary in upper leaf axils, consist of 5-20 staminate disc flowers surrounded by 1-5 fertile pistillate flowers with tiny tubular corollas. Phyllaries fused into a shallow cup, 5-8 lobed. Wind-pollinated.
FRUITS and SEEDS:Achenes lack a pappus, obovate, +/- flattened, 2-3 mm long, brown to near black, covered with minute glistening bumps.
POSTSENESCENCE CHARACTERISTICS:Roots survive, but foliage dies back in cold winter climates.
HABITAT:Alkaline plains, edges of salt marshes, cultivated fields, pastures, roadsides, waste places. Often grows on poorly drained, heavy alkaline or saline soils, but not limited to these soil types.
DISTRIBUTION:Common throughout California, but more troublesome in other western states; to British Columbia, Central U.S., Montana, Texas. To 2500 m (8200 ft).
PROPAGATION/PHENOLOGY:Reproduces vegetatively from creeping roots and by seed. Roots seldom exhaust their energy reserves. Deep roots can remain dormant for long periods under intense competition and produce new shoots under drought conditions. Seed primarily disperses near the parent plant, but can move long distances in water and with agricultural machinery. Newly matured seed can be dormant. Seed can survive ~ 8 months submergence in water. Information on seed viability and longevity is lacking.
MANAGEMENT FAVORING/DISCOURAGING SURVIVAL:Cultivation can disperse root fragments. Deep roots can survive repeated cultivation for several years. Alternating wheat with summer fallow or growing perennial hay crops such as alfalfa can help suppress infestations. Managing pastures to prevent overgrazing helps to suppress colonization.
SIMILAR SPECIES:San Diego marsh-elder [Iva hayesiana A. Gray] is a non-weedy rare native perennial in southwestern San Diego County that closely resembles poverty sumpweed. Unlike poverty sumpweed, San Diego marsh-elder has flower heads with separate phyllaries. Ragweeds [Ambrosia spp.] are most easily distinguished by having toothed to lobed leaves.
CONTROL METHODS:
Poverty weed is a perennial forb native to California and much of the Western United States. It is a common component of many alkali plains plant communities where saline, poorly-drained, heavy clay soils occur. However, it is not completely limited to these areas. It may also persist along roadsides, cultivated fields and salt marsh areas. Although a native plant, poverty weed has been listed as a noxious weed due to the following problems. It is highly competitive when established in agricultural fields and may significantly reduce crop yields. Heavily infested rangeland areas have little grazing value due to the low palatability of the plant. Additionally, there have been reports that povertyweed is a selenium accumulator and may be toxic to livestock when ingested. However, this is very rare due to the unpalatable nature of the plant. Poverty weed pollen is also highly allergenic and plants may cause contact dermatitis in sensitive individuals. There is very little known about the population biology of poverty weed. As with many perennial forbs, seedlings are rarely seen. Seed production may often be limited by insect predation. Established stands of the plant commonly spread asexually via buds on lateral roots, and large clones of a single genotype may form. Poverty weed also appears to be an obligate outcrosser, requiring pollen from other plants for successful fertilization. Seed viability is unclear, but studies have shown some seed may be viable after two years of fresh water storage. Seed are not wind dispersed, but may be transported in soil and water. In rangelands, poverty weed is problematic generally only where overgrazing has occurred. In agricultural fields, poverty weed generally spreads by root pieces created by tillage. As a natural component of the native plant community, poverty weed should not be eradicated. However, where it causes problems, the following management information can be applied. Poverty weed is generally very difficult to control due to a deep root system with high-energy reserves. Intensive tillage over a three-year period failed to effectively control poverty weed and is not recommended. Handpulling is very difficult and must be repeated as new shoots emerge. Gloves and long sleeves should be worn due to the irritating properties of the foliage. Controlled burning is not expected to be effective for management since poverty weed is a deep-rooted perennial and a natural component of many grassland communities that experience periodic fire. Because poverty weed is a native species, there are no biocontrol programs established. There is little research on mowing, but regrowth is likely to occur with no long-term damage to the plant. Only a limited number of effective chemical options are available. Research from Canada has shown 2,4-D applied at 2 lb ae/A or 2,4-DB applied at 1.3 lb ae/A over a five year period was highly effective. Picloram applied at 0.75 lb ae/A is also effective, but this compound is not registered in California. Research from Australia has shown that high volume spot applications of 0.3% v/v clopyralid, 0.2% v/v picloram + 0.8% v/v 2,4-D were effective for short-term control. Extended control for 1 or 2 years and a very high level of control for 3 years was obtained with 0.1% v/v picloram + 0.4% v/v 2,4-D, 0.8% v/v dicamba, and 0.72% v/v glyphosate applied spray-to-wet.