Just like the human world, the plant world has freeloaders that let other plants do all the work while they kick back and enjoy themselves, said Jerry Goodspeed, Utah State University Extension horticulturist.

“The mooching plant I am talking about is dodder,” he said. “Dodder is a parasitic plant. Instead of developing a root system that processes chlorophyll to produce food from the sun on its own, this weed invades other plants and sucks the energy it requires from them. It spends its entire life simply eating and using the nutrients and water another plant has absorbed and produced.”

There are not many parasitic plants, but dodder is a common sight this time of year, said Goodspeed. It looks like a yellow to orange-colored mass of strings that appear to be growing on top of other plants.

“Dodder germinates from a seed in early summer,” he said. “Instead of sending a root system into the soil, it puts all its energy into producing a stem that spirals around as it grows, looking for a host plant to invade. This small seedling can only live a couple of weeks without a host.”

Once it locates a host plant, it attaches itself by twining tightly around a stem and inserting a small haustorium into the plant. This appendage allows dodder to steal nutrients and water from its host and begin its life as a parasite — completely dependent upon another plant for survival, Goodspeed said. As dodder grows, it sends out more stems that spiral around to eventually intrude on other plants.

Like all plants, dodder flowers and produces seed as it matures, he said. One plant produces thousands of small black seeds that can lay dormant in the soil for up to 20 years before germinating. About 5 to 10 percent of the seeds it produces germinate the following year.

“Even though dodder is dependent upon its host plant for survival as a parasite, it is very specific as to the plants it will invade,” Goodspeed explained. “Oddly enough, one of its favorite hosts is field bindweed (morning glory). It would be nice if these two ugly weeds would simply kill each other off. However, dodder is not a good option for control of field bindweed.”

Dodder also attacks some of our favorite plants, he said. Other hosts include tomatoes, melons, asparagus and alfalfa. It can take over a patch of basil and other herbs and can also damage some annuals.

“The best way to control dodder is to prevent it from ever gaining access to your property,” said Goodspeed. “Be certain to buy only clean, certified seed, and make sure to keep all annuals or perennials clean of dodder. Also, when bringing soil into your yard, check to be certain it does not have dodder.”

If you are already dealing with this pesky weed, remove it and the host plant as quickly as possible. Next, grow plants that are not a desirable host. Ornamental grasses and woody plants are not bothered by dodder. If you cannot eliminate the host plant, apply a pre-emergent in the spring to kill it as it germinates in the early summer, he concluded.


By: Julene Reese - Sep. 14, 2004