Dodder: To Kill or Not to Kill

Southwest Yard & Garden | September 23, 2017

Question:
What are the beautiful golden strands that show up from nowhere, and seem to attack the goatheads? Can they be moved from one patch to another where it is not growing yet?

B. Stanley, Chaparral, NM

Dodder strands on puncturevine (credit: Dr. Beck)

Dodder forming mats on weedy roadside (credit: J. French, NMSU Extension Plant Pathology Specialist) 

Answer:

In order to fully address your question, I have consulted with NMSU Weed Specialist, Dr. Leslie Beck. Those golden strands are from a climbing parasitic plant commonly known as dodder of the genus Cuscuta.  It is a close relative of morningglory and the dreaded field bindweed, which are all in the plant family Convolvulaceae. You may have seen time-lapse video footage of vine tips making slow, circular, swaying motions as a way of searching for sturdy branch to climb. Dodder grows in a similar way.

Dodder germinates from seed in the soil during the hottest, wettest point in the summer. Once it germinates it immediately searches for a host. A particular favorite is puncturevine (also known as ‘goatheads’) which was the subject of last week’s column. Pigweed, purslane, and common vegetable crops such as tomato, cucurbits, and young pepper plants are also common hosts. Often found as spooky, pale yellow, noodle-like mats growing on top of weeds along roadsides and in areas of high foot traffic where the soil is more compacted and native species have a hard time getting established.

Flowers of dodder develop throughout the summer, depending on location and moisture, and are very small and whitish in color. If conditions remain favorable, each flower produces a basket-like pod with 2 to 4 seeds.  Seeds have been known to stay viable for as long as twenty years while waiting for an opportune time to sprout and parasitize a new host plant.

Dodder forming mat on puncturevine and pigweed (credit: Dr. Beck)

Dodder has no leaves and no chlorophyll. Therefore it does not photosynthesize. Neither does it establish roots of its own.  Once dodder attaches, its haustoria (root-like structures) spread within the host plant stems, allowing dodder to steal nutrients, sugars, and water. 

If you want to get rid of dodder in your yard, the best way to eradicate dodder is to kill or remove the host plant if it is considered a weed, ideally, before dodder produces its own seed. Dodder is short-lived in our area. It does not overwinter inside the host plant tissues. Therefore, interrupting the life cycle prior to seed production is the best way to control dodder.

Dodder flowers in San Juan County (credit: Dr. Beck)

While dodder infects puncturevine, like any good parasite, it does not cause enough damage quickly enough to prevent the production of new goathead seed (which can remain dormant in the soil for approximately seven years).  Even though it will not completely control puncturevine, biological control of weedy species is an important part of an overall integrated pest management strategy.  Combining multiple practices to injure a target weed is the best method for successful and sustainable weed management.

If you want to encourage dodder spread, the best practice is to let it form and drop seed for the next monsoon. Theoretically, you can collect dodder seed and disperse it along weedy patches on your property. Attempts to physically move dodder in order to control a new host are not likely to work since the tender haustoria will be ripped in the move. 

Dodder haustoria penetrating the stem of a host plant. (credit J. French, NMSU Extension Plant Pathology Specialist)

Keep the questions coming!

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, office: 505-865-7340, ext. 113.

Links:

Click here for more information about puncturevine (Tribulus terrestris).

Click here for more information about dodder (Cuscuta spp.).

NMSU Plant Diagnostic Clinic Featured Diagnosis: Dodder

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook page (@NMDesertBlooms)

Please copy your County Extension Agent and indicate your county of residence when you submit your question!