There are many dodder species in the U.S. They are annual weeds that are obligate parasites – dodder seedlings must find a suitable host plant to attach to and extract nutrients from within a short time after they emerge. The host range is fairly large, but some plants are resistant to dodder.
For the remainder of this year, the only thing you can really do is to carefully clip out as much of the dodder vines as possible, with emphasis on removing and discarding its little seed capsules. Or if you are willing to sacrifice your plants, you can tear them out and destroy them.
Dodder vines will die after the first frost, and its seeds will germinate next spring. The pre-emergent herbicide “pendimethalin” is effective in preventing emergence of dodder seedlings. Pendimethalin is the active ingredient in several products (granulars and sprays) used to prevent weeds in lawns and landscape beds. If you decide to use pendimethalin, it should be applied by early April because it has little to no herbicidal activity on emerged weeds. Feel free to contact me if you need more information.
Todd L. Mervosh, Ph.D.
Weed Scientist & Diagnostician
The Ct Agricultural Experiment Station
Valley Laboratory
153 Cook Hill Road, P.O. Box 248
Windsor, CT 06095
Tel.: 860-683-4984