Dodder: A Plant Parasite - August 19, 2009
Jeff Schalau, Associate Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County
Have you ever seen a plant that appears to be covered with something that resembles golden spaghetti? Iíve most often observed it at 50 MPH on the roadside, but if you stop and take a close look, you may notice that itís rooted in the ground and also growing into another host plant. This viny mass is a parasitic plant called dodder. If you havenít seen it before, watch for it and take a closer look.
Dodder was once classified as being in the morning glory family (Convolvulaceae), but was more recently given its own family: Cuscutaceae. According to the UDSA Plants Database (plants.usda.gov) are over 150 species of dodder worldwide and all are in the genus Cuscuta (at least the last time I checked). However, letís leave this discussion to the systematic botanists that spend their lives arguing for and against the naming of new species.
Dodder is a true obligate parasite: the host plant receives no benefit from the dodder and dodder must have a host plant to survive. Dodder appears leafless (it does have small scales) and lacks sufficient chlorophyll to produce any significant amount of its own food. It attaches to a host plant with small appendages (haustoria) which allow it to extract carbohydrates, water, and nutrients. It is usually a golden color, but can also be tinged with red or purple.
The flowers are often numerous, white, pink or yellowish, and 2 to 4 mm long. Flowers normally appear from early June to the end of the growing season. The flowers produce small fruits which are about 1/8th inch in diameter and contain 1 to 4 seeds. Dodder seeds drop to the ground and germinate the next growing season if a suitable host is present. The seeds may remain dormant for up to twenty or more years. The seeds require moisture and sunlight for germination and do not need to be associated with a host plants to germinate.
Following germination, dodder seedlings must attach to a suitable host within a few days or they will die. Much like a pole bean, dodder seedlings swirl around until they encounter a potential host plant. If the host plant contains suitable foods, then the haustoria penetrate the stem. Once the above-ground connection is made, the original connection to the soil where the seed germinated is no longer necessary and this portion of the plant shrivels away. It is an annual plant and dies each winter in our temperate climate.
Among the many species of dodder, hosts can vary widely. Economically important host species include alfalfa, lespedeza, flax, clover and potatoes. Ornamental plants susceptible to dodder include chrysanthemum, dahlia, helenium, Virginia-creeper, trumpet-vine, English ivy and petunias. The dodder I have seen in Yavapai County is likely a native species because it had colonized roadside shrubs such as catclaw and annual sunflowers. One Arizona species of dodder also colonizes puncturevine.
The easiest way to control dodder is to manually remove when possible. This is not always an option if the host is a woody plant. Many references cite the use of pre-emergent herbicides to prevent dodder germination. I have not seen any cases that have warranted this action. If you see dodder in your area, it may be prudent to control it manually. Seeds have also been known to be dispersed in irrigation water where ditch systems are present. To see what dodder looks like, see the links at the bottom of this page.
Iíd also like to invite the public to attend the vegetable gardening seminars being offered by Yavapai County Master Gardeners in both Prescott and Cottonwood. The Cottonwood vegetable gardening seminars will be presented between 6 and 8 pm on August 12, September 22, October 27, November 24, January 26, and February 23 at the Cottonwood Public Safety Building, 199 S 6th Street, Cottonwood. For a complete list of topics, dates, and locations, go to the Yavapai County Cooperative Extension website at: cals.arizona.edu/yavapai/.
The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at firstname.lastname@example.org and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/.
Color photo and information from Doug Von Gausig's Naturesongs website
Line Drawing by Kittie Parker
Color photo from Utah Department of Agriculture
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Last Updated: August 13, 2009
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