That's not Silly String-it's Dodder!
Looking like Silly String in your garden but in reality a whole lot creepier, dodder is, thankfully, an uncommon garden weed.
It’s a plant vampire. (Plampire? Vamplant?)
Lacking the ability to produce chlorophyll, and therefore its own food, dodder sinks its “fangs” (called haustoria) into its victim and draws nutrients and water from it. Depending on the health and vigor of the host plant, it will weaken and possibly die.
Dodder produces many small white flowers in clusters along the length of its wiry stems. These flowers develop into hard-coated seeds. Each dodder plant can produce thousands of seeds in a season, which drop to the ground waiting to sprout the following season. The seeds have with the potential to be dormant but viable in the soil for up to 20 years. (yikes-they’re mummies too!)
When the seed germinates it has a few days to find a suitable host or it will die, as it is unable to produce food of its own. When it does contact a host, it sinks its fangs…er, haustoria in and loses its connection to the soil, living completely on the host.
Even if the visible stringy stems are removed from the host plant, the haustoria left behind in the host plant are capable of resprouting a new dodder plant. If you dispose of removed dodder stems in contact with a suitable host plant, they can attach and begin growing again. (Zombies?)
Are you creeped out yet?
Control of dodder is difficult and it can take several years to achieve control. Any post emergent herbicide that controls dodder will also damage the host plant. This may be fine if dodder infects your weeds, but ornamental plants usually must be sacrificed if they get infected. It may be possible to prune dodder out of hardy plants if the infection is limited.
Once removed, careful cleaning of the infected site is necessary to remove any small pieces that may remain. Avoid any activity that may spread dormant seeds from the affected area to “clean” areas, or bring them to the surface (weed-whacking, tilling, mowing). Regular application of pre-emergent herbicides may be necessary to prevent the seeds from sprouting.
If you see dodder in your garden, don’t hesitate to control it quickly or you will be fighting this monster plant for many seasons to come.