Field Dodder

What is field dodder?

Field dodder is a parasitic plant. It has no real leaves, makes very little of its own food, and survives by coiling thin yellow-orange stems around other plants and pushing small pegs called haustoria into them to draw out water and nutrients. Once you know the look, field dodder identification is easy: a tangle of orange string draped over a crop or flower bed, with no green foliage of its own. You may see it listed as Cuscuta campestris or Cuscuta pentagona; UC IPM notes both names are used for this plant.

It weakens everything it grabs. Hosts lose vigor and yield, seedlings can be badly stunted, and multiple attachments can kill established plants. Weakened hosts are more open to insects, disease and nematodes, and Oregon's Department of Agriculture notes dodder can carry viruses such as beet yellows and cucumber mosaic between plants. Because each plant can drop thousands of long-lived seeds, one season of neglect can leave a seed bank that reinfests a field or garden for decades.

Field Dodder identification: what to look for

You will usually notice dodder by its color before anything else. Look for yellow to orange threads looping over and through a plant, then follow a strand to see where it is pressed against the host stem. Check for tiny clustered flowers along the strands, and look at the soil line: an attached dodder plant has no stem running down into the ground.

• Stems: Slender, twining stems ranging from pale green to yellow or bright orange, branching repeatedly and reattaching as they grow, until they form dense mats over the host.
• Leaves: None to speak of, only tiny scales about 1/16 inch long.
• Flowers: Bell-shaped, cream to white or faintly pink flowers about 1/8 inch long, in compact clusters, from late spring through fall.
• Seed capsules: Small capsules, each holding two or three rough seeds about 1/16 inch across. Seed set starts near the first point of attachment and spreads outward.
• Seedlings: Yellowish threads with no leaves, rising from the soil in spring. A seedling that does not find a host within roughly 5 to 10 days dies.
• Attachment: Stems coil tightly around the host and press haustoria into it. After attachment, the original link to the soil withers.

Where it grows in the United States

Dodders grow across much of North America; Oregon's Department of Agriculture calls the genus widely distributed, and UC IPM notes dodders are most common in the Americas. Field dodder has an unusually broad host range, so it can turn up wherever its hosts grow, from alfalfa and sugar beet fields to vegetable gardens and flower beds. Seeds sprout at or near the soil surface in spring once the soil warms to about 60 F, whether or not a host is nearby.

UC IPM lists hosts including alfalfa and sugar beet; vegetables such as carrot, onion, pepper, potato, tomato and melons; ornamentals such as chrysanthemum, impatiens, periwinkle and petunia; and weeds such as field bindweed, lambsquarters, pigweed and Russian thistle. The seed has no built-in way to travel, so new infestations usually trace back to people: contaminated crop seed, soil on equipment or boots, infested plant material, poorly composted manure, and weedy field edges and irrigation canals.

Field Dodder look-alikes

A few plants get mixed up with it:

• Japanese dodder (Cuscuta japonica): An Asian dodder found in parts of California. Its stems are thicker and round, like strands of spaghetti, it seldom flowers, and it can smother large shrubs and small trees, especially citrus. In California it is under an eradication program, so report it to your county agricultural commissioner instead of handling it yourself.
• Clover dodder (Cuscuta epithymum): Another orange-threaded dodder, but it generally sticks to clovers, while field dodder attacks a long list of crops, flowers and weeds. Telling dodder species apart depends on details of the tiny flowers and how the seed capsules open, so send a sample to your Extension office if the species matters.

How to get rid of field dodder

Pulling, digging and mowing: In a garden, hand-pull or hoe dodder seedlings before they latch on; cultivation after attachment does little. Once dodder is attached, cut the host stem about 1/8 to 1/4 inch below the attachment point, because haustoria left in the host can regrow. Freshly pulled dodder can grab a healthy plant again, so let it dry where no hosts are within reach, and bag anything with flowers or seeds for the trash. For heavy infestations, the surest fix is to pull out the infested hosts and replant with something dodder cannot use. In fields, close mowing below the attachment point before seed set helps, and burning works only when the infested host tissue burns too. Soil solarization may not kill the hard-coated seed.

Cultural control matters most, because the right conditions keep it from coming back.

• Plant only dodder-free seed; contaminated crop seed is one of the main ways dodder moves.
• Where dodder has been bad, grow nonhost plants such as grasses, lilies and other monocots, or rotate away from host crops for several years; NMSU suggests about 4 to 5 years where practical.
• Control host weeds such as field bindweed, lambsquarters and pigweed, and keep field edges and irrigation canals clean.
• Use only well-rotted manure, and clean tools, equipment, boots and clothing before moving from infested ground to clean ground.
• Scout susceptible crops regularly (NMSU suggests about every two weeks) and remove patches before they set seed.

Herbicides: UC IPM says chemical control is usually unnecessary in home gardens. Where dodder keeps returning, a pre-emergence herbicide applied before dodder germinates in spring, such as trifluralin in the UC IPM example, can reduce seedlings, followed by spot removal of escapes; Purdue cautions many pre-emergence products do not last the whole season. After attachment, most herbicides cannot kill dodder without hurting the host. Pelargonic acid works on dodder but damages any plant tissue it touches. In an alfalfa study cited by NMSU, glyphosate gave the best control, followed by propyzamide and imazethapyr, but glyphosate is nonselective and injures crops and lawn grasses where it lands. Use only a product labeled for your crop or site. The label is the law. If you hire someone to spray, make sure they hold your state’s pesticide applicator license; the rules for each state are in our pesticide applicator license guide.

Keeping it from coming back

Keep dodder from arriving in the first place: plant only dodder-free seed, use well-rotted manure, and clean mud and plant debris off tools, tires and boots before you move from an infested area. Watch garden beds, vegetable rows and alfalfa in late spring and early summer, when new seedlings are latching on.

If dodder gets in, the most important rule is to stop it from setting seed. Seeds can stay viable in the soil for more than 20 years, so every plant you remove before it flowers saves you years of follow-up. Mark infested spots, rotate them to nonhost plants, and keep checking for several seasons.

Questions we get about field dodder

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