Answer: Good old-fashioned dodder is weird in that it germinates from seeds and then becomes parasitic on the host plants. It doesn't need roots once it attaches itself to other plants because they supply all the food and moisture it requires.
In ornamental beds you can treat the soil with a pre-emergent herbicide such as WeedzStop (an organic product with corn gluten as active ingredient). This product is sold by Gardener's Supply Co. (www.gardeners.com; ph# 800/863-1700). You will need to reapply it every so often throughout the summer to keep the dodder at bay.
Q&A Library Searching Tips