Back in my younger days before I joined the Ohio State University Extension office in Wood County, I was a greenhouse production manager. Also, during that time, I had a full head of curly hair.
One of the crops we produced was the F1 hybrid Begonia (Begonia semperflorens). Another common name for this plant is the wax begonia. These begonias were raised in 4 ½ inch containers with 10 to a flat. I remember raising rows and rows of these flats of begonias.
The reason the begonias stick out in my mind, is one day while walking the rows, I came across a parasitic plant growing in the flats. The parasitic plant was Dodder. Dodders are plants belonging to the morning glory family, Convolvulaceae. There are somewhere between 100-170 species worldwide with 13 species reportedly found in Ohio. The two most common species found in our state are Common Dodder also known as Swamp Dodder (C. gronovii), and Field Dodder or Five-Angled Dodder (C. pentagona).
The hallmark of dodders is their thin, tendril-like stems that encircle the stems of their host plants. Dodder stems range in color from yellow to orange to red depending on the species and age. Some species, but not all, have tiny scale-like leaves. Although most dodders have some chlorophyll, it is insufficient in photosynthesizing enough sugar to support a singular lifestyle. Mature dodder plants also lack roots. When I came across the dodder in the begonias it looked like a tangled mass of fishing line laying on top of the plants.
Dodders are obligate parasites; they cannot make a living without their plant hosts. They invade their hosts in this case the begonias using specialized, peg-like structures called haustoria (singular haustorium). The dodder’s haustoria are considered modified roots and are used to extract water, carbohydrates, and nutrients from their host’s vascular bundles. Vascular bundles are the transportation mechanisms for water and nutrients throughout the plant.
Dodders can attach themselves to an amazing range of host plants, often at the same time. Some Dodder species are annuals, while others are perennial flowering plants. Regardless of type when their flowers pollinate, they produce two to four large seeds.
In the greenhouse situation with our begonias, we were mystified as where the dodder came from. We used new pots, flats, and soil. The greenhouse was also relatively clean. Often in the landscape or in field crops the situation as to where dodder shows up it is also a mystery. Our best guess was birds often fly in and fly out of the greenhouse. We suspected the bird droppings contained a dodder seed. This was just a theory and of course could not be proven.
Dodders are stealthy plant invaders using a move that has been described as mimicking a computer virus. Research published in 2018 in Nature showed that dodders send microRNA into their hosts that silence the encoding of genes that would normally support defenses of the host plant. One of those defenses is a protein that clots the flow of nutrients to the site of the dodder’s haustoria. Without the “anticoagulant” protein, the plant’s lifeblood keeps flowing into the dodder.
Dodder wreaks havoc on its plant hosts in other ways. Plant stress caused by the heavy extraction of the host’s resources can weaken plants making them even more susceptible to plant pathogens as well as environmental calamities such as drought.
Dodder causes annual crop losses worldwide that are measured in tens of millions of dollars. These parasitic plants have been found sucking the life out of over 100 species of plants including alfalfa, clover, soybeans, and plants in gardens such as petunias and tomatoes.
Hopefully, you will not encounter dodder in your landscape. However, if you do control is twofold. It is thought that dodder in Northwest Ohio has an annual life cycle. Research published in 2008 in the journal Flora casts some doubt that dodder always has an annual life cycle. The researchers observed a possible perennial characteristic of clover dodder (C. epithymum) by overwintering vegetatively on its most common perennial host Scotch heather (Calluna vulgaris). This proves once again that all plants in Horticulture there’s always a caveat!
Not knowing for sure if dodder can overwinter, control starts with destroying the dodder and unfortunately the host it is attached to with an herbicide. Once the dodder and the host plant are dead, the following spring add a pre-emergent herbicide to the area in an around the infected plant. After the following growing season, and no dodder has reappeared it is safe to replant that area again.
Dodders have some wicked sounding common names such as wizard’s net, devil’s guts, and witch’s hair. However, they are not devoid of providing some benefits. Dodders contains a range of compounds that may be beneficial in human medicine. They have long been used in Chinese folk medicine. A review published in 2017 in Biomedicine & Pharmacotherapy reported dodders harbor molecules with possible therapeutic benefits including potential antiviral and anticancer activities.
Of course, some claims may be overblown. In preparing this article, I came across a few dodder products touting to reverse hair loss. I am considering a bulk purchase.
