Dodder entwined around field bindweed View Higher resolution Photos

Introduction:
Dodder (Cuscuta and Grammica), is a twining yellow or orange plant sometimes tinged with purple or red. Occasionally it is almost white. The stems can be very thin and thread-like or relatively stout (a species characteristic).

Dodder is classified as a member of the Morning-Glory Family (Convolvulaceae) in older references, and as a member of the Dodder Family (Cuscutaceae) in the more recent publications. Welsh et al. reports twelve species of Cuscuta in Utah while Weber (1986) separates this family into two genera with one species in Cuscuta and five species in the genus Grammica. Weber's separation is based on the shape of the stigma.

Dodder parasitizes various kinds of wild and cultivated plants, and is especially destructive to alfalfa, lespedeza, flax, clover and potatoes. Ornamentals attacked included chrysanthemum, dahlia, helenium, Virginia-creeper, trumpet-vine, English ivy and petunias. Dodder is particularly troublesome where alfalfa, clover and onion are grown for seed because dodder seed is difficult to remove from the desired seed crop and can be spread with infested seed. Its water, minerals and carbohydrates are absorbed from the host through haustoria that penetrate the host's tissue. In dodder the haustoria are modified adventitious roots.

Dodder is said (Wilson, et al.) to contain some chlorophyll in the buds, fruits and stems, but the amount of food manufactured in this tissue is of little significance to the survival of the plant.

The flowers are numerous, white, pink or yellowish, small (2 to 4 mm long depending on species), and can be borne in tight balls or in a loose cluster (again depending on species). Flowers normally appear from early June to the end of the growing season. The fruit is about 1/8 th inch in diameter, with thin papery walls and contain 1 to 4 seeds. The seeds are yellow to brown or black, nearly round and have a fine rough surface with one round and two flat sides.

Dodder produces seed that drops to the ground and germinate the next growing season if a suitable host is present. If no suitable host is present, the seed may remain dormant for five years. Smoothseed Alfalfa Dodder ((Cuscuta approximata Bab. Var. urceolata (Kunze) Yuncker) is reported to produce over 16,000 seeds 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."

Dodder seedlings must attach to a suitable host within a few days of germinating or they die. The young seedling is sensitive to touch and yellowish stem gropes in the air until it makes contact with a plant. The contact is made firm by one or more coils about the stem. If this plant happens to contain foods suitable to the dodder then a secondary stimulus is aroused which causes root-like branches (haustoria) to form and penetrate the stem. The basal part of the parasite soon shrivels away so that no soil connection exists.

Other names of this parasite include love vine, strangleweed, devil's-guts , goldthread, pull-down, devil's-ringlet, hellbine, hairweed, devil's-hair, and hailweed.

Dodder as a vector of disease:

Phytoplasma, the cause of more than 200 so-called yellows diseases (previously thought to be caused by virus) are spread by several different vectors to include leafhoppers and dodder. Dodder has been shown to spread the yellows disease pear decline, aster yellows, tomato big bud, vinca virescence and elm phloem necrosis. In addition, phloem-inhabiting `rickettsialike' bacteria have been found to be present in dodder (Mount and Lacy).

Allowing dodder to spread in a field or garden area is asking for an increase in the plant diseases this parasite is capable of spreading.

Control:

Its wide host range and the long life of its dormant seeds make dodder hard to control and nearly impossible to eradicate. Dodder seed can be spread by irrigation water, in the manures of livestock that have eaten infested alfalfa, or along with the seed of crops that were infested with dodder.

Preemergent herbicides such as DCPA (Dacthal), applied to the soil in the spring prior to seed germination will prevent this pest. Follow label directions! The Dacthal label can be found at http://www.cdms.net/LDat/ld4HM005.pdf.

Pulling and destroying dodder infected plants is recommended. Dodder must be destroyed before it produces seeds or infestations will spread. Once established, dodder appears in patches in the field. Cutting the host plant prior to the dodder producing seed helps reduce the quantity of seed for the following year. Planting an infested field with an immune or resistant crop such as cereals, corn, soybeans, velvetbeans or cowpeas assists in control.

The use of a 2,4-D type herbicide or contact herbicide directed at infected hosts and dodder plants is effective in killing established parasitic plants (as well as the host).

References used:

Anon. http://www.nwcb.wa.gov/weed_info/Cuscuta_approximata.html
Anon. 1996. Farm Chemicals Handbook 96. Meister Publishing Company.
Anon. 1986. Integrated Pest management for Potatoes in the Western United States. University of California, Division of Agriculture and Natural Resources Publication 33316.
Anon. 1953. Plant Diseases : The Yearbook of Agriculture. US Dept of Agriculture, Washington, D.C.
Anon. 1950. South Dakota Weeds. State Weed Board Publication No. 5.
Anon. 1996. Weed Control Manual. Meister Publishing Company.
Anon. 1960. Weeds of the North Central States. North Central Regional Publication No. 36.
Curtis, C.C. 1916. Nature and Development of Plants. Henry Holt and Company, New York.
Fernald, M.L. (Ed.) 1950. Gray's Manual of Botany, Eighth Edition. American Book Company.
Mount, M.S. & G.H. Lacy. 1982. Phytopathogenic Prokaryotes, Volume I. Academic Press.
Seymour, E.L.D. (Ed.). 1941. The New Garden Encyclopedia. Wm. H. Wise and Co., New York.
Weber, W.A. 1972. Rocky Mountain Flora. Colorado Associated University Press, Boulder, CO.
Weber, W.A. 1987. Colorado Flora: Western Slope. Colorado Associated University press, Boulder, CO.
Welsh, S.L., N.D. Atwood, S. Goodrich, L.C. Higgins. A Utah Flora, Second Edition. Brigham Young University, Provo UT.
Wilson, C.L., W.E. Loomis & H. T. Croasdale. 1962. Botany, Third Edition. Holt, Rinehart and Winston.

Placed on the Internet: August 28, 1996

Comments on this page should be addressed to Dr. Curtis E. Swift, Area Extension Agent, Horticulture
Colorado State Extension
2775 US Hwy 50, Grand Junction, CO. 81503
voice: 970-244-1834
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