Smoothseed Alfalfa Dodder
(Cuscuta approximata Bab. Var. urceolata (Kunze) Yuncker)

Family: Cuscutaceae

Description and Variation: Smoothseed alfafa dodder is an annual, parasitic plant that is yellow or orange or reddish. It twines about other plants and obtains nourishment from them by means of "suckers". The flowers are in small (two to three mm long), yellowish, and somewhat fleshy dense clusters. The seeds are about 1/16 inch long, irregularly round with a rough texture. Dodder seeds resemble alfalfa seeds, but they can sometimes be distinguished from alfalfa seeds when they cling together in small clusters. This plant has aerial roots. There are no green plant parts on this parasitic species. There are about 50 species of dodder in the Northern Hemisphere, and three species impact the Northwest regions.

Economic Importance: Detrimental: Dodder is parasitic and damaging to leguminous crops, especially alfalfa and clover. It also impacts vegetable and forage crops, ornamentals, native plants, and weeds. Dodder can suppress or kill the host plants.

Habitat: Dodder is found in older farming areas, roadsides, ditches, and fields.

Geographic Distribution: This species is thought to be native to the old world, but several varieties are now well established in North America, although new world plants are all referable to the var. urceolata.

History: Dodder is found in the western United States, Eurasia, and Africa. It was reported to be a problem in the late 1950’s from the Walla Walla area. Research on dodder and alfalfa began in the 1960’s.

Growth and Development: Dodder germinates on the ground. A small root anchors the plant, while at the same time, a thread-like stem grows upward. When the stem comes into contact with an object, it begins to twine around it. If the object is a suitable green plant, the dodder develops suckers that penetrate the host plant and absorb food. At this time, the small root disappears, and the dodder is completely parasitic upon its host plant. New branches are continually sent out which also develop suckers and deplete the host plant.

Reproduction: Dodder is an annual plant that reproduces by seed. Over 16,000 seeds are produced per plant. The seed viability times range from 20 to over 60 years and germination can be delayed for years. The seeds can travel by water along irrigation ditches. Moist soil and sunlight is required for germination. The seeds can germinate without a host plant, unlike the seeds of most parasitic plants.

Response to Herbicides: Please refer to the latest edition of the Pacific Northwest Weed Control Handbook.

Response to Cultural Methods: Rotate dodder infested fields with grasses, which are immune to dodder and will not be a host crop. Prevent new infestations by cleaning combines and farm equipment. Hay with dodder seed should only be used in feed lots.

Response to Mechanical Methods: It is easier to prevent dodder establishment, than to eradicate it. When dodder is confined to small areas, it is recommended to cut it, let it dry, and burn it.

Rationale for Listing: Dodder is a parasite that often kills the host plant and it quickly spreads. This parasite reduces the yield of any plant it infests, with the biggest impact in the west to alfalfa, and to tomatoes in California. Seed production is lost, and harvesting machinery needs to be cleaned to prevent further spread of this noxious species.

References:

Dawson, J.H., F.M. Ashton, W.V. Welker, J.R. Frank and G.A. Buchanan. 1984. Dodder and Its Control. Farmer’s Bulletin No. 2276, United States Dept. of Agriculture.

Hitchcock, Cronquist, Ownbey and Thompson. 1969. Vascular Plants of the Pacific Northwest. University of Washington Press. Vol. 4:89-90.

LaRea, J. D. 1980. Gilkey’s Weeds of the Pacific Northwest. Oregon State University Press.

Weed Alert - Parasitic Dodder. British Columbia Ministry of Agriculture and Food.

Rohse, E.D. Feb. 20, 1998. Clover Growers Warned About Weed Dodder. Capital Press newspaper article.