Garden Column for the Salisbury Post

Darrell Blackwelder

July 14, 2005

     The butterfly garden at the Horticultural Demonstration Garden on Brenner Avenue has been invaded by a strange, almost alien type plant. A yellow, spaghetti-like plant called dodder seemed to come from nowhere and is entangling bedding plants and shrubs.       

     Dodder is an annual parasitic plant that consists of thin thread-like stems that are bright-yellow to orange in color. The yellow parasite quickly attaches itself to a host plant. Years ago, botanists classified the plant as a member of the morning glory family.      Dodder, unlike mistletoe with green leaves, is a true parasitic plant that extracts water and nutrients from host plants. Dodder has no leaves and must extract water and carbohydrates from the host plant.
     Dodder produces small clusters of white to pink flowers in the early summer, producing seeds which have the capability of surviving in the soil up to sixty years! Evidently the dodder at the butterfly garden must have arrived as seed on transplanted material.                                      

     When dodder seed germinates if a host plant is not within 1 - 3 inches of the initial germinating seed the seedling will die. Germinating dodder seedlings develop a small ineffective root which can support the seedling for only a couple of days.  Just after germination small dodder seedling sways around in search of the host plant. Dodder coils around the host in a counter-clockwise direction producing very small sucking appendages called haustoria. These appendages penetrate its victim and extract its food. The feeding mechanism is very similar to that of a plant fungus. The small initial root dies once the parasite establishes its feeding appendage. Dodder grows rapidly, up to 3 inches per day and continually draining the host plant of nutrients.
     Prevention by planting clean seed is the best way to control dodder. Keep ornamental beds clean of seed-producing plants, because once dodder becomes established, eradication is almost impossible.        Physically removing the parasite can be attempted, but once dodder is established it is almost impossible to avoid damage to the host plant. Removal of both dodder and host plant is recommended to eradicate.
     Control with pre-emergence herbicides is somewhat effective; however, these products must be applied prior to the germination. Unfortunately, pre-emergence herbicides can damage a variety of bedding plants and perennials. Many annuals and perennials are sensitive to pre-emergence herbicides so always check the label before application.                

    Glyphosate (Roundup) will kill dodder, but also kills or may kill or severely damage the host plant. Depending on your planting, soil sterilization may be a viable option to consider.

Darrell Blackwelder is an agricultural agent in charge of horticulture with the North Carolina Cooperative Extension Service in Rowan County. For archived garden columns or other information, visit the Rowan County Master Gardener web site at www.rowanmastergardener.com , e-mail Darrell_Blackwelder@ncsu.edu