HPIPM:Dodder

Taxonomy

Domain	Eukarya
Kingdom	Plantae
Phylum	Magnoliophyta
Class	Magnoliopsida
Superorder	Asteranae
Order	Solanales
Family	Convolvulaceae

Scientific Name

Cuscuta

Common Name

dodder

Dodder (Cuscuta cephalanthi)

Compiled by Joe Julian Colorado State University, Douglas County Extension and Evette Allison, Montana State University, from the following sources:

http://www.coopext.colostate.edu/TRA/dodder.html

http://main.nc.us/naturenotebook/plants/dodder.html

http://sanangelo.tamu.edu/agronomy/pdf/03112.pdf

http://pubs.caes.uga.edu/caespubs/pubs/PDF/C867-6.pdf

http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7496.html

http://www.floridata.com/ref/c/cusc_spp.cfm

http://www.weedalert.com/weed_pages/wa_dodder.htm

Identification and Life Cycle

Dodder (Cuscuta cephalanthi) is a parasitic vine with smooth, wiry, twining stems that attach to a host plant with tiny suckers. Only the seedlings have roots. The tangled stems are usually orange, but may be yellowish, whitish, or greenish or even tinged with red or purple. The stems turn black when the plant dies. One dodder plant looks like a fat yellow thread tangled in the weeds. Large numbers of them crawl over shrubbery to form blankets that look like masses of wet excelsior. The tiny leaves are scale like and almost invisible, whereas the numerous clusters of little waxy cream colored 5-petaled flowers and subsequent 1/8 in (0.3 cm) seedpods are more noticeable. There are 2 to 4, 3-sided brownish seeds in each 2-celled capsule. Botanists recognize some 150 species of dodder, though some authorities split out a few of them into the genus Grammica. Dodder species cannot be identified until they develop mature flowers and most people can't tell them apart even then.

Habitats

There are Cuscuta species native to most every part of the temperate and tropical world. Habitat varies with the host plant, but they generally parasitize plants that grow in disturbed areas. Prefers open areas and partial shade.

Impacts

Native plants, ornamental shrubs, trees, groundcovers, and crop plants can be infested with dodder. The bright yellow stems of dodder can be readily seen against the foliage of the host plants. The impact of dodder varies from moderate to severe reductions in growth of the host plant and, in some instances, may result in complete loss of vigor and death. The severity of an infestation depends on the growth stage of the host plant at the time of initial dodder attachment. The greatest growth reduction occurs when dodder attaches to seedlings. Established host plants are usually not killed by a dodder infestation, but when multiple attachments are made to the same host plant, death can occur. The weakened state of infected plants also predisposes them to losses from other maladies such as disease, insect, and nematode invasions.

The greatest concern in cultivated agriculture is typically in seed production of alfalfa and clover. The similarity in appearance and size of dodder seed to the crop seed causes difficulty in cleaning seed. The roughness of the dodder seed often is utilized to remove dodder from contaminated seed, but some contamination commonly remains. It is a major economic problem for such crops as alfalfa, clover, and flax. Dodder is the only weed restricted legally as a contaminant in crop seed in each state of the continental United States. American dodder (C. americana) and golden dodder (C. campestrisis) are particularly damaging agricultural weeds.

Although dodder is not thought of as a poisonous plant, cows and horses have shown colicky symptoms after eating it. Dodder can also carry plant viruses, including Phytoplasma, which is responsible for many of the "yellows" diseases.

Biology and Ecology

Seeds usually emerge from shallow soil depths. The entire seedling looks like a yellow thread with no stem-root differences. Dodder must attach to a host within a few days or the seedling will die. In Colorado, dodder typically attaches to alfalfa and various clovers. Seedlings emerge as an arch and the plant tip extends and straightens upward after emerging. A slow counter-clockwise rotation occurs after extension. The stem entwines around any elongated object within 1 to 3 inches of the seedling. After initial twining, dodder will introduce haustoria into the host vascular system. If this attachment is successful, the stem portion in contact with the soil withers. The dodder seedling then draws sustenance from the host plant. Shading can inhibit initial growth and attachment. The degree of twining, branching and attachment varies among species. Some species have tendrils for twining. A dense mat will develop over the host as the dodder spreads.

Dodder seed lacks obvious dispersal mechanisms and is likely spread by people through the movement of soil, equipment, or in mud attached to shoes and tires. Dodder seed may also be transported in infested plant material or be present as a contaminant in crop seed. Water may play a role in seed dispersal, particularly for dodder species near aquatic environments.

Biological Control

Several disease organisms are known to infect dodder, including Fusarium tricinctum and Alternaria spp., which attack swamp dodder (C. gronovii) and Alternaria alternata and Geotrichum candidum, which attack field dodder (C. pentagona). Researchers in China have found that a conidial suspension of Colletotrichum gloeosporioides can selectively control Cuscuta chinensis and C. australis in soybeans. Difficulty in culturing and applying these organisms has limited their use or commercialization.

Resistant Varieties of Crops

Breeding programs aimed at developing dodder-resistant varieties are not known to exist, however, some varieties of normally susceptible species have been reported to have some resistance. For example, several varieties of processing tomatoes, a plant that is generally susceptible to dodder parasitism, have been observed to be either totally resistant or tolerant to dodder attack.

Mechanical and Cultural Control

Remove all plants or portions of plants infected by dodder. Ideally it should be removed before the dodder flowers and produces seed. To date, dodder cannot be controlled through a selective postemergent herbicide application. However if the host plant is killed, the dodder plant will also die. Dodder seed can be controlled with the preemergent herbicides Kerb and Casoron (check label to see if herbicides are safe to host ornamentals). Other options include soil sterilization with Basamid (a soil sterilant).

Thick forage growth can shade dodder seedlings limiting development and growth; however, dodder establishment still is possible. Healthy forage plants will have a greater tolerance to the parasite. Crop rotation with nonhost plants for five years will minimize the infestation of dodder seed in the soil. Any grass plant including small grains and corn is a suitable non-host crop.

Planting nonhost plants can be an effective means of managing a dodder infestation. Plants that are not hosts of dodder include grasses (e.g., corn) and many other monocots (e.g., lilies). Plants that grow primarily during winter (crucifers and legumes), as well as transplanted trees and shrubs that have bark, are usually good alternatives. Dodder cannot penetrate tree bark, but it can penetrate tree foliage, if it is able to contact it. Select plants that are nonhosts of the species of dodder present. Also, be sure to remove weeds in these plantings so that the weeds don't serve as hosts for dodder and increase the amount of dodder seed in the soil.

Dodder seedlings are difficult to find, but if they are observed before they attach to a host, remove them by cultivation or by hand-pulling. If dodder is observed soon after attachment, prune the infected portion of the host plant 1/8 to 1/4 inch below the point of attachment, otherwise the dodder may regenerate from the haustoria left embedded in the host plant. Pruning of trees and shrubs generally has been of little benefit unless dodder is confined to one or two branches that can be removed without destroying or disfiguring the whole host plant.

If no host plants are present, cultivated dodder plants can be left on the soil surface to dry and die. However, if freshly removed dodder is allowed to contact a healthy host plant, a new connection sometimes occurs. If the dodder plants have set seed, remove the plants from the area to prevent future infestations. Place plants in a plastic bag and dispose of it in the trash.

Dodder seed has been observed to survive soil solarization, probably because of its hard seed coat. Although composting studies have not been conducted, it is believed that composting would kill most dodder seed because higher temperatures are reached in the composting process than in solarization. In agricultural settings, cultivate dodder before it attaches to a host plant; if cultivation is done after dodder attaches to the host, it is of no benefit. Hand-pulling, cutting, or mowing can also reduce dodder infestations. The host plant must be broken off, cut, or mowed just below the point of dodder attachment (about 1/8 to 1/4 inch) for these methods to be effective. Close mowing is an effective management tool for dodder in alfalfa. Burning reduces a dodder infestation as long as the invaded tissue of host plants is destroyed along with the dodder to prevent regeneration of the dodder from embedded haustoria. Burning kills only some of the dodder seed; the amount of seed destroyed depends on the duration and intensity of the fire.

Examples of herbicides that can be used to manage dodder

Consult herbicide labels for additional rate, application, and safety information. Additional herbicide information can be found at http://www.greenbook.net.

Herbicide Active Ingredient trade name	Mode of Action	Product per Acre	Application Time or Growth Stage
Alfalfa grown for seed
Protamide	Group 3 (microtubule inhibitor)
*Kerb 50-W		furrow irrigation 3-4 lb/A, flood or overhead sprinkler irrigation 3 lb/A	For furrow irrigation, incorporate lightly at time of application and irrigate within seven days. For flood or overhead sprinkler irrigation apply 0.5-1 inches of water within 1-3 days of applying herbicide. For effective control, product must be applied before dodder germinates.
pendimethalin	Group 3 (microtubule inhibitor)
*Prowl H20		4 qts./A	Apply to dormant established alfalfa. Apply before alfalfa exceeds 10 inches in height after first mowing/beating. Once the alfalfa reaches 10 inches in height or if the alfalfa has been mowed/beaten two or more times, Prowl H2O must be applied with drop nozzles directing the spray so that there is little to no contact with the foliage.
Alfalfa
Ammonium salt of imazethapyr	Group 2 (Inhibition of acetolactate synthase ALS)
*Pursuit		6 oz/A	For best results in suppressing dodder (Cuscuta spp.), apply Pursuit with crop oilconcentrate or methylated seed oil after dodder has emerged but prior to or soon after attachment. Apply to alfalfa in the fall or spring when crop is dormant or semi dormant.
pendimethalin	Group 3 (microtubule inhibitor)
*Prowl H20		4 qts./A	Applications can be made in the fall after the last mowing/cutting, during winter dormancy, in the spring, or between cuttings. Applications should be made prior to the alfalfa reaching 6 inches in regrowth.

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality. Updated Nov 2008

References

For more information and images please visit IPM Bugwood: http://www.ipmimages.org/search/action.cfm?q=dodder