I once overheard somebody complain that some kids killed her tomatoes with silly string. It was none of my business so I didn’t butt in, but I knew that wasn’t the problem. Driving toward the beach recently I spotted several dense patches of the culprit that destroyed her tomatoes and it wasn’t any prank from a spray can.
Dodder (Cuscuta sp.)is a parasitic plant like mistletoe. It attaches itself to its host by modified roots called haustoria. Once connected, dodder extracts whatever nutrients it needs from its victim. Unlike mistletoe, dodder plants contain no chlorophyll and have nothing but tiny scales for leaves. Dodder must sponge nutrients and all its energy from host plants.
Most dodder is bright yellow to orange and can form dense patches. Not every plant is susceptible, however. Grasses including corn are immune as are most cool-season plants and vegetables. Dodder is rarely seen before soil temperatures are warm.
Tomatoes, potatoes, peppers, eggplant, melons, beets and carrots are prime targets. English ivy, mums, impatiens and petunias are vulnerable ornamentals. I’ve seen it on azalea too. In waste places I see it mostly on lambsquarter and redroot pigweed.
Sometimes dodder has been called vampire weed for the way it sucks the energy from its host. According to legend, garlic will repel vampires, but dodder is a tougher adversary. Garlic and onions are very dodder susceptible.
Dodder plants are usually hard to find when they haven’t attached to another plant. They spread by seed and seedlings can only live briefly without a host plant. That doesn’t sound very imposing. However, those seeds can remain dormant but viable for 50 years. Individual plants also can produce several thousand seeds.
I must admit that I have always been somewhat fascinated by it. Flowers are small, white and often barely noticeable. They look a little like tiny lily of the valley flowers. Fruits look like peas without the pods. When dodder grows it constantly reattaches itself to the host plant or surrounding ones creating a strangling mass of gold string.
As you might suspect, dodder can be difficult to control. It’s a good thing this unusual plant is not super common. Young crop seedlings are least able to overcome the parasite. Weakened plants are also more prone to diseases and insect damage. Furthermore, most chemicals that might kill dodder would also kill host plants.
Generally speaking, the best way to control dodder chemically is through the use of pre-emergent herbicides. They keep dodder seeds from germinating. They also keep crop seeds from germinating, but if crops are already growing that technique could work.
On small areas, continued hand removal helps, but debris should be destroyed. Catching it early before flowering is critical. Finding nearby infested areas and attacking it there can also be helpful.
I have never tried it, but unless dodder is parasitizing poisonous plants it’s edible. I suppose it could be boiled and used as a pasta substitute. I’m not interested. Numerous sources report its use medicinally to treat various internal ailments, but dodder is not a major player in herbal medicine.
Ted Manzer teaches agriculture at Northeastern High School.