News release: Dodder: A Parasitic Weed

Tim Baker, MU Extension Horticulture Specialist
102 N. Main, Suite 1, Gallatin, MO 64640
660-663-3232, bakert@missouri.edu

Release Date: August 6, 2015

Headline: Dodder

I recently attended “Prairie Days” at the Dunn Ranch in Harrison County. My main objective was to see their bison herd, which I was able to do.  But before that, I took a quick jaunt through a native prairie area with a Missouri Department of Conservation botanist, to identify many of the native species of plants growing there.

It wasn’t long before we came upon several examples of dodder. Dodder is a fascinating plant, but not something you want to grow in your garden.

Dodder is usually described by gardeners who call me as a pale yellow, spaghetti-like plant which is taking over the area in their garden where it has become established.

Dodder is a summer annual weed, which produces yellowish/orange to near-white, leafless vines and tendrils.  These vines twist around the host plant, and quickly engulf it. These plants are true parasites, and derive all their nourishment from the host plant.

After germinating from a seed, the plant sends up an initial vine which must attach itself to a suitable host.  If it does not do this quickly, the plant will die.  When it finds a suitable host, dodder inserts root-like haustoria into the host plant to feed on it.

As the plant matures, it will form tiny flowers.  These flowers will, in turn, form seeds.  It may form as many as 5,000 seeds on a single plant.  If the plant is not removed before this stage, the seeds will fall to the ground, and you will soon have a dodder problem.  Because of a hard seed coat, these seeds are long-lived in the soil, and will germinate year after year, and the dodder infestation will increase, unless you take measures to control it.  In a garden, that means removing it as soon as you see it.  Don’t give it a chance to flower and produce seeds.

Unfortunately, this usually means removing the host plant as well as the dodder.  I once talked to a gardener who told me she kept removing the dodder from the plant, but it kept coming back.  That is because once established, the dodder can regenerate from the haustoria imbedded inside the host plant.  So it’s usually a good idea to remove and destroy the host plant as well.

Dodder can also regenerate from stem pieces.  That’s right.  If you carry pieces of it somewhere else, and it happens to land on a suitable host, then it can establish itself on the new host in short order.  Did someone say, “noxious weed?”  I believe it is considered in that category, in some parts of the country.

Dodder is also known to transmit plant diseases.  It has been shown to vector pear decline, aster yellows, tomato big bud, vinca virescence, and elm phloem necrosis.

Unfortunately, dodder is difficult to eradicate, once it is established, especially in crops.  Fortunately, it isn’t common in our part of the country. Because it is leafless, chemical control is difficult.  Some pre-emergent herbicides are effective, but once it has germinated, it is there for the season.  Home control is much easier.  Simply remove the dodder and host plants, and be on the lookout for new seedlings.  But you may have to keep after it for several years before it is entirely removed.