Nobody wants to look outside and see a mound of yellow, spaghetti-like strands covering the petunias. If this describes your view, you have a dodder problem. (Either that or you missed the garbage can while cleaning up dinner.)
There are about 150 species of dodder (Cuscuta spp.), a twining parasitic annual found throughout the world, and they infest both agricultural fields and home gardens. The slender, twining, yellow stems attach to host plants and can spread to form dense mats.
Different species of dodder attack different plants. Some garden favorites are preferred hosts, including carrots, melons, tomatoes, chrysanthemums, impatiens, and petunias. Dodder does not infest grasses and lilies.
Damage
Dodder weakens plants by taking their water and nutrients for itself and by smothering them with blankets of its yellowish strands. Though dodder doesn’t usually kill its host plant, the host is nevertheless doomed, at least in a garden setting. Because the parasitic vine twines around the host plant and taps into its stems, you usually can’t get rid of it without getting rid of the host plant too. If you can see where dodder has attached itself and prune below the lowest point of attachment, you might be able to save the host plant.
Control
It’s critical to get dodder out of the ground (with its victims) before it sets seed. Each plant can produce thousands of seeds, and those seeds can remain viable for decades. Once you’ve seen dodder in your garden, watch the area very closely and pull out seedlings as they sprout. Another strategy is to replant the area with grasses or other nonhost plants. If dodder seedlings don’t find a suitable host within five to ten days, they die.
—photo courtesy of the Kemper Center for Home Gardening at the Missouri Botanical Garden.