JoAnne Skelly: What are those orange strings that cling to plants?
July 24, 2017
A reader sent me photos and questions recently stating: "I've seen this "growth" on various garden plants at just a couple homes in my neighborhood. They struggled to get rid of it. Just recently, I found this growing out in the desert on BLM land about a mile or two past our neighborhood, and would like to know what it is, if it's going to spread, does it kill its host, and if I should do something about it."
Once you have seen dodder, it's easy to recognize. This parasitic annual plant is quite distinctive because it looks like a big ball of orange string covering its host plant. It infests crops, ornamentals, native plants and even weeds. However, I am being a bit misleading because dodder can range in color from pale green to yellow to orange. It gets its energy from the host plant, reattaching continually to its original host, and then spreading its shoots to other nearby plants.
People are the primary disseminator of dodder spreading it with soil and equipment as well as on shoes and tires. Of course, it also spreads when infested plant material is moved or if it's present in seeds. It can spread via water, too. Dodder flowers from late spring through fall, setting most of its seeds in late summer. Even though only about five percent of seed germinates each year, the remainder can lay dormant for more than 20 years. Seeds can even survive soil solarization.
Dodder doesn't always kill its host, although it can reduce the growth of the infested plant. The vigor of the host plant, its stage of growth and the severity of the infestation are influential factors in host response and whether it survives.
Managing dodder takes commitment, because controlling it takes more than one treatment over multiple years. If you see newly attached dodder strings on your plants, prune the infected part of the host 1/4 inch below the point of attachment of the dodder. Regular, repeated hand-pulling or cutting year after year can reduce infestations. When it is found on herbaceous plants, it's easiest to remove the entire host plant, placing it in a sealed garbage bag to prevent spread of pieces or seeds. Dispose of the bag in the trash.
Chemical treatment is rarely called for in home gardens and landscapes, although some preemergent herbicides are listed for dodder control and can reduce populations when applied before seeds germinate.
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JoAnne Skelly is Associate Professor & Extension Educator, Emerita at University of Nevada Cooperative Extension. She can be reached at firstname.lastname@example.org.