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Dodder |
By Curtis Swift, Colorado State University Cooperative Extension, Horticulture
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. 
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.
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.
The seedlings must attach to a suitable host within a few days of germinating or they
die. Once the Dodder seedling finds a host
plant, it quickly twines itself
around the plant's stem. Dodder always twines in a counter-clockwise direction. Next,
Dodder will lose its connection to the ground. It now totally depends upon its host. The
basal part of the parasite soon shrivels away so that no soil connection exists. Its
water, minerals and carbohydrates are absorbed from the host through haustoria that press
up against the stem of the host plant and penetrate the tissue. In dodder the haustoria
are modified adventitious roots. Dodder rarely kills its host plant, although it will
stunt its growth.
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. These seeds drop 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.
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.
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.
Pulling and destroying dodder infected plants is recommended. Dodder must be destroyed before it produces seeds or infestations will spread.
Preemergent herbicides such as DCPA (Dacthal), applied to the soil in the spring prior to seed germination will prevent this pest. 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). Always read and follow label directions when using herbicides.
Photos: Judy Sedbrook
