Not all plant diseases are caused by parasitic microbes, some are caused by parasitic weeds. The dodder vine is one of those weeds. Dodder attaches itself to healthy plants and makes them more vulnerable to other diseases and insect pests. To help understand more about the fascinating parasitic dodder weed I will explain plant relationships and the conditions that are favorable for the dodder to survive. Best practices for ridding your landscape of this vine are included.
I want to briefly explain the different ways certain plants live together in nature before I explain dodder. I find that this will better define the distinction dodder has when compared to other notable plant relationships familiar to most plant enthusiasts.
Many older publications list dodder as being in the morning glory family, Convolvulaceae, which includes some notable field and garden weeds as field bindweed, Convolvulus arvensis; hedge bindweed, C. sepium; ivy leaf morning glory, Ipomoea hederacea; tall morning glory, I. purpurea and pitted morning glory, I. Iacunosa, (Muenscher, 1980; ARS USDA, 1971; Uva, Neal, and DiTomaso, 1997; Sinclair, Lyon and Johnson, 1987).
However, more recent publications have placed the dodder genus, Cuscuta, in its own family, Cuscutaceae. Therefore, I will follow the taxonomy presented by Magee and Ahles (2007) as follows.
If you are interested in pursuing the taxonomy and identification of the few dodder species inhabiting the New England states, the text Flora of the Northeast by Magee and Ahles (2007) is your best start if you are comfortable using botanical dichotomous keys. They provide a taxonomic key to the more commonly encountered species complete with range maps listing eight dodder species; five native and three introduced from Europe.
Westbrooks (1993) lists over fifty native dodder species known to occur in the United States and Canada. The United States Department of Agriculture’s website https://www.plants.usda.gov/core/profile?symbol=CUSCU lists both native and introduced dodder species with range maps for the United States including Westbrooks’ listings. When visiting this site, click on the ‘subordinate taxa’ tab to view specific species and their accompanying range maps.
Other plant scientists report that there are between 150 to 170 dodder species worldwide (Sinclair et al, 1987; Powell and Linquist, 1992).
I want to briefly explain the different ways certain plants live together in nature before I explain dodder. I find that this will better define the distinction dodder has when compared to other notable plant relationships familiar to most plant enthusiasts.
When different plant species in close proximity to one another share the same environment they are said to be in a symbiotic relationship. For example, the different native trees and shrubs in our New England landscapes are in symbiosis or in a symbiotic relationship.
However, biological scientists have described three types of specific symbiotic plant relationships that bare distinction; commensalism, mutualism, and parasitism (Towle, 1989).
Commensalism is a type of symbiotic relationship where one plant gains some benefit(s) (the commensal) and the other (the host) neither benefits nor suffers any harm (Towle, 1989; Buchsbaum, 1957). Epiphytes are frequently cited as examples of this type of symbiotic relationship. Epiphytes or epiphytic plants use other plants for some type of support to further their life cycle. Epiphytes like algae and lichens are common in our temperate ecosystems but are more commonly seen in tropical ecosystems, particularly in rainforests as seen in figure 1. For example, the tropical trees that support specific orchids, bromeliads, and mosses (the epiphytes) high in their canopies allow these specific plants to gain more sunlight than they otherwise would when growing below the canopy level or on the very shaded ground (Towle, 1989). These and other similar epiphytes get their nutrients from rainfall, dew, mist, fog, and decomposing organic matter caught in trees providing a nutrient base for nutrient release.
Keep in mind that epiphytes, while gaining a more favorable position in the dense tropical forest for sunlight, do not draw water and nutrients from their much larger host trees. Lichens and algae, being epiphytes, also do not draw water and nutrients from their supporting hosts.
Mutualism is another type of symbiotic relationship where two different organisms live together in mutual benefit (neither harms the other). Lichens, as seen in figure 2, and mentioned above, are frequently cited examples. In nature, lichen species are very widespread but unusual in that they are composed of two different but compatible organisms. One organism or component is a fungus and the other organism or component contains chlorophyll and is photosynthetic. Therefore, the fungus is referred to as the mycobiont and the photosynthetic partner is the photobiont. The photosynthetically active photobionts contain chlorophyll and are specific green algae or a particular cyanobacterium species.
How does this type of symbiosis work? The mycobiont or fungal part of the lichen is the visually distinct thallus or lichen body we all see when observing these “funny looking plants” growing on rocks, soil, tree bark, asphalt, gravestones, and other places. Figure 3 shows lichens specific to rocky ledges. The fungal component or lichen body (mycobiont) absorbs nutrients and water and the photobionts (photosynthesizing algae and cyanobacteria) that live inside the lichen body function to provide carbohydrates to both the fungal component and themselves (REA, 1999).
This particular and some think peculiar mutualistic relationship, is very unique in the plant world because the fungus alone or the particular algae/cyanobacteria alone cannot colonize a suitable substrate by themselves and live independently (Purvis, 2000). Why? Laboratory experiments have proven that not all species of fungi or all species of algae can undergo the specialized compatible association necessary to form lichen. Fungi that can are called lichenized or lichen-forming fungi.
According to Brodo, Sharnoff, and Sharnoff (2001), lichen body shapes and forms are determined by the fungal component of this type of symbiotic relationship.
Brodo et al (2001), states that because lichens are composed of compatible fungal species with a compatible algal or cyanobacterium species they are determined to be dual organisms and therefore, very different from straight species of plants like red oak, eastern white pine, or American chestnut, etc., that have their own genetic makeup distinguishing them from one another as woody plants.
Parasites that are plants obtain their nutrient needs from another plant. It’s that straightforward. They are not commensals like epiphytes nor are they mutualistic organisms like lichens. A parasitic plant uses its host plant in a long – term symbiotic relationship. The parasitic plant contains no chlorophyll. It cannot make its own food by way of photosynthesis. Instead, it has evolved to parasitize its supporting host plant to draw water and nutrients in order to stay alive and reproduce.
There are several flowering, seed-producing parasitic plants that are distributed around the world. Some important economic parasitic plants are in the following groups; broomrapes, witchweed, American (true), and dwarf mistletoes and dodder (Powell and Lindquist, 1992).
Dodder vines are classified as being a disease organism by plant pathologists and botanists. Plant diseases can be caused by an array of living organisms (e.g. parasitic plants, fungi, bacteria, viruses, etc.), as well as by non-living events such as drought, low temperature extremes, poor soil conditions, and the like (Powell and Lindquist, 1992).
How a particular disease develops depends on three important factors; a suitable pathogen, a susceptible host, and a favorable environment. The plant disease triangle (figure 4) illustrates this point. It is commonly known by all plant pathology students and others working in the plant industry treating plants for diseases. For each disease causing organism(s) or environmental (non-living) events, the triangle helps determine and clarify the factors necessary for a disease to flourish, take hold and contribute to plant decline, even plant death (Ellis and Bradley, 1992).
Each of these factors in the triangle needs to be in synchrony for a specific plant disease to develop and flourish (Powell and Lindquist, 1992). For example, if you have the fungal spores of needlecast disease on your eastern white pine but no disease development, one or two of the other disease triangle factors are not contributing for the needlecast disease to develop.
Figure 5 shows a generalized disease triangle for the dodder vine species I battle at The Country Club on goldenrod.
Dodder spp. seeds drop from the parent plant or are deposited in the soil from the previous spring or summer, overwinter and germinate the following year. Depending on the species, seed germination can occur from April to October and some seeds can lie dormant in the soil for several years before environmental conditions are favorable for germination (Schrock, 2004). Dodders have reduced or scale-like leaves.
When seeds germinate they form soil penetrating roots that support seedling – sized vines that are governed by strong phototropism and grow only upward on to their susceptible host in a counterclockwise growth habit (see figure 6) (Sinclair et al, 1987). Attaching to a susceptible host while anchored by its own roots may take several weeks but when a susceptible host is found by way of water vapor gradients and volatile chemical attractants, vine modified above ground root-like organs known as haustoria, attach to the host and penetrate it along its stem. Haustoria are the specialized parasitic structures used by parasitic plants to draw water and nutrients from its host.
When enough haustoria (figure 7) penetrate the host plant stems, the dodder loses its root connection to the soil and they break off or wither away leaving the parasitic dodder vine flourishing, extracting sustenance from its host for continued development which includes growth, flowering, fruiting, and seed production for the next year (Sinclair et al, 1987).
Dodder appears as a yellow-orange, leafless, thread-like vine that grows over its hosts’ leaves, branches, and stems as an entangled, smothering web (see figure 8).
It looks like a form of yellowish-orange angel hair spaghetti capturing your interest as you investigate by pulling it off or away from your garden plants. You will notice that it is attached by haustoria and combined with its twining nature, breaks off easily when pulled but the left behind portions are still viable and continue to grow and parasitize its host (Sinclair et al, 1987).
Host plants susceptible to this parasitic vine range from vegetable crops to ornamental and herbaceous garden plants; including some woody plants. The dodder vine is therefore a disease when it successfully parasitizes its host. Generally, host plants are weakened by dodder, not immediately killed.
When applicable, plant dodder resistant varieties, pull out vines before they flower, and continue to monitor infested plants to be sure you keep up with dodder removal.
Dodder seeds are widely distributed as a contaminant in sugar beet, clover, alfalfa, and flaxseed lots. Buy dodder weed free seed (Powell and Lindquist, 1992). Dodder seed can be spread by various animals and contaminated soil left on digging tools and plows.
Do not add dodder infested plants and soil to your compost pile because you’ll have a greater risk of contaminating clean garden areas with your own compost (Ellis and Bradley, 1992).
Remember, dodder seed can live in soil for several years until environmental conditions are favorable for germination. If left uncontrolled, dodder will spread farther and farther each year, producing seed for new plants and contaminating the soil seed bank as an endless disease to some of your desirable plants.
Dodder, as a parasitic plant, weakens its host plants making them more susceptible to other diseases, insect pests, and less resilient to bouts of drought, temperature extremes, and other environmental problems.
ARSUSDA (Agricultural Research Service, United States Department of Agriculture). 1971. Common Weeds of the United States. Dover Publications, Inc., New York. 463p.
Brodo, I. M., S. D. Sharnoff and S. Sharnoff. 2001. Lichens of North America. Yale University Press, New Haven, Connecticut. 795p.
Ellis, Barbara W. and Fern Marshall Bradley (Eds). 1992. The Organic Gardener’s Handbook of Natural Insect and Disease Control. Rodale Press, Emmaus, Pennsylvania. 534p.
Magee, Dennis and Harry E. Ahles. 2007. Flora of the Northeast. A Manual of the Vascular Flora of New England and Adjacent New York. (2nd Ed). University of Massachusetts Press, Amherst. 1214p.
Powell, Charles C. and Richard K. Lindquist. 1992. Ball Pest and Disease Manual. Disease, Insect and Mite Control on Flower and Foliage Crops. Ball Publishing, Geneva, Illinois. 332p.
REA (Research & Education Association). 1999. REA’s Problem Solvers, Biology. A Complete Solution Guide to any Textbook. Research and Education Association, Piscataway, New Jersey. 1064p.
Schrock, Denny (Editor). 2004. Ortho Home Gardener’s Problem Solver. Meredith Gardening Books, Des Moines, Iowa. 624p.
Sinclair, Wayne, A., H. H. Lyon and W. T. Johnson. 1987. Diseases of Trees and Shrubs. Cornell University Press, Ithaca, New York. 575p.
Uva, Richard H., J. C. Neal and J. M. DiTomaso. 1997. Weeds of the Northeast. Cornell University Press, Ithaca, New York. 397p.
Westbrooks, Randy G. 1993. Exclusion and Eradication of Foreign Weeds from the United States by USDA APHIS in Biological Pollution: The Control and Impact of Invasive Exotic Species. Bill N. McKnight (Editor). Indiana Academy of Science, Indianapolis. 261p.
Bruce Wenning has been on the ELA Board of Directors since 2003. He has university degrees in plant pathology and entomology and is the horticulturist at The Country Club in Brookline, Massachusetts.
Dodder, a parasitic vine that winds itself around other plants, can be a major threat to the health and beauty of ornamental grasses like basket grass Left unchecked, dodder will drain nutrients, block sunlight, and eventually kill the host plant Removing dodder properly and timely is crucial for saving your basket grass.
What is Dodder?
Dodder, also known scientifically as Cuscuta species, is a parasitic climbing vine that lacks leaves and chlorophyll It grows by attaching sucker-like growths called haustoria to the stems and leaves of host plants Dodder draws all its nutrients and water from the host, weakening and eventually killing it.
Dodder has thin yellow orange or pale green stems that twist around basket grass stems and leaves. Tiny white bell-shaped flowers form that produce seeds to spread the infestation. Dodder spreads rapidly by vine growth and seeds.
Identifying Dodder on Basket Grass
- Look for yellow, orange or green threadlike vines winding tightly around stems and leaves
- May cover large sections of the plant
- Can form dense mats several feet across
- Reduced vigor and death of stems where dodder has attached
- Presence of small white dodder flowers
Remove Dodder Manually
Early detection and thorough manual removal provides the best control of dodder in basket grasses.
- Wear gloves to protect from skin irritation
- Unwind dodder stems carefully to avoid damaging basket grass
- Sever dodder vines at the point of attachment to the host
- Remove every trace of dodder from plant
- Prune back heavily infested stems and leaves
- Bag and dispose of dodder debris immediately
- Check plant daily for any remaining dodder vines
- Repeat manual removal as needed until plant is clear
For large infestations, you may need to cut back the basket grass significantly. As long as the main crown is healthy, it will regrow.
Use Neem Oil
Neem oil naturally disrupts dodder growth when applied directly to infestations.
- Mix neem oil with water per label instructions
- Thoroughly coat dodder vines and attachments sites
- Reapply every 7-10 days for 2-3 weeks
- May take several treatments to fully control dodder
Prevent Dodder Infestations
Preventing dodder from taking hold is ideal. Follow these tips:
- Inspect plants routinely for early spotting
- Maintain plant health with proper care
- Isolate and inspect new plants before introducing
- Remove nearby weed hosts like bindweed
- Plant dodder-repelling plants like marigolds as companions
- Control spread by cleaning tools and shoes after working in dodder-infested areas
Catching infestations early and taking quick action is key to successful removal. Check basket grasses routinely for the sight of any dodder vines. At the first sign, begin manual removal and neem oil treatment. With persistence, your beloved ornamental grass can be freed from this parasitic invader.
How Does Dodder Harm Basket Grasses?
Dodder is a destructive pest that can ruin the appearance and health of ornamental grasses like basket grass. Here’s how it damages plants:
- Saps nutrients and moisture from the host grass
- Blocks sunlight from reaching the host’s foliage and stems
- Interferes with photosynthesis, starving the host
- Inhibits air circulation around plant
- Outcompetes the host for resources
- Stunts growth and yellowing of foliage
- Weakens and eventually kills the host plant
- Spreads quickly to surrounding plants
Left unmanaged, a dodder infestation can destroy an entire planting of ornamental grass. Don’t wait to take action at the first signs of dodder vines.
When to Remove Dodder from Basket Grass
For the best results, remove dodder immediately upon detection. Young seedlings are easier to control before they proliferate.
Signs dodder must be removed:
- Yellow or orange threadlike stems wrapping around ornamental grass
- Haustoria attachments along leaves and stems
- Small white dodder flowers visible
- Sections of weakened, yellowing grass where dodder has attached
- Dense web-like dodder mats covering grass
Catching infestations when just starting ensures the grass can recover fully. Mature dodder may require aggressive removal of heavily infested sections.
Will Basket Grass Recover After Dodder?
With prompt removal of dodder, basket grass has an excellent chance of fully recovering. Ensure all traces of dodder are removed, especially the haustoria connections. Prune back severely infested stems and leaves to healthy tissue. Destroy all dodder debris.
The extensive rhizome root system of basket grass helps regenerate new growth after dodder removal. Maintain proper care of the grass by:
- Watering deeply 1-2 times per week
- Applying fertilizer to nourish regrowth
- Removing competing weeds
- Dividing congested clumps
New leaves and shoots will emerge within a few weeks after eliminating dodder. Full recovery can take 1-2 months. Some permanent stunting may occur on heavily infested plants.
Dodder Control Methods
Controlling dodder requires attacking it from several angles:
Manual Removal
Physically remove all vines, stems, flowers and connections by hand. Prune infested sections of the plant. Bag and dispose of dodder debris immediately.
Organic Herbicides
Apply neem oil or horticultural vinegar to smother dodder and disrupt growth. May take multiple applications.
Prevent Seed Production
Remove flowers and seed capsules to prevent spread.
Weed Management
Eliminate nearby weed hosts like bindweed that allow dodder populations to thrive.
Sanitation
Clean tools, shoes, and equipment to avoid spreading dodder seeds and vines to uninfested areas.
Tips for Dodder Removal from Basket Grass
- Check plants routinely for early detection
- Wear gloves and long sleeves when removing dodder by hand
- Unwind stems carefully starting from the top
- Sever vines at the attachment point to the host
- Use pruners, scissors or a sharp knife for removal
- Bag and dispose of dodder debris immediately
- Apply neem oil after manual removal
- Re-inspect and remove any remaining traces in following days
- Maintain optimal growing conditions for recovery
Staying vigilant and taking quick action at the first sign of dodder offers the best chance of saving basket grasses from this destructive pest. With persistence, your ornamental grass will thrive once again.
Can Dodder Be Controlled Without Chemicals?
Yes, dodder can be controlled manually without the use of chemical herbicides:
- Hand pull vines carefully from stems and leaves
- Use pruners or scissors to sever dodder vines at attachment points
- Prune off badly infested sections of the plant
- Remove all traces – double check for any remaining vines or haustoria
- Dispose of dodder debris far from planting beds
- Routine inspection and manual removal
- Good sanitation practices for tools and shoes
For home gardeners concerned about using chemicals, manual control allows basket grasses and other plants to be freed of dodder organically. It requires diligence to remove every trace, but is safe and effective when started early.
Left unchecked, dodder can quickly overrun and destroy ornamental grasses like basket grass. Identifying dodder early and taking swift action through manual removal and neem oil treatment can eliminate infestations before they get out of control. Stay vigilant with routine monitoring, maintain the vigor of your grasses, and control nearby weed hosts. With persistence and care, your cherished basket grass will thrive once again after removing this destructive invader.
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How We Are Dealing With the Invasive Weed Dodder | Gardening with Creekside
FAQ
What herbicide kills dodder?
Is dodder harmful to humans?
What does dodder do to plants?
How to remove weeds from potted plants?
How to control dodder weed?
Pruning is useful if you want to control the Dodder weed in the early stages. Once there’s a sign keep a close watch on the Dodder-prone area. If you see Dodder attached to host plants, prune the host plant too. You may need to prune 1/4th of an inch below the attached point. This is to be done to avoid the regeneration of this parasitic plant.
How do you get rid of dodder weeds?
Dodder doesn’t thrive on Grasses, Lilies, Legumes, and Crucifers. Pruning is useful if you want to control the Dodder weed in the early stages. Once there’s a sign keep a close watch on the Dodder-prone area. If you see Dodder attached to host plants, prune the host plant too. You may need to prune 1/4th of an inch below the attached point.
How do you get rid of dodder?
Remove small infestations of dodder by hand and manage large ones with mowing, pruning, burning, or spraying herbicides to thwart seed production. Prune host plants 1/8 to 14 inch (5 mm. to 36 cm.) below the point of attachment.
How does a dodder plant kill a host?
Once attached, dodder plant extracts nutrients and water from the host, predisposing the host to disease and insect invasion, affecting fruit set and yield, and even killing off the host. As previously mentioned, dodder is a parasitic weed. It emerges as a rootless shoot that must attach itself to a host within a few days.