Dodders
are Parasitic
By
Q: I recently planted some petunias and
noticed a small yellow tendril coming out of the petals. It was oddly foreign to the petunia. Do you know what it was?
Steve B.
A: It sounds like there was some dodder
imported with your petunias. Dodder, Cuscuta
spp, is a parasitic annual plant that infests many ornamentals, natives,
crops, and weeds. All dodders are
parasitic, but species vary in their degree of host specificity. For example, some species are found on only a
few host plants in salt marshes, flats, and ponds. Other species are found on a wide range of
cultivated plants and weeds. Dodder is
usually spread by people through the movement of infested plants, or as seeds
carried in soil, equipment, or for example, mud attached to shoes and tires. Dodder seed may also be present as a
contaminant in crop seed.
Dodder species have slender twining or threadlike stems that vary in color from
pale green to yellow or bright orange. They
may be leafless or have small, scale-like triangular leaves approximately 1/16
inch in length. The bell-shaped flowers
are cream colored, approximately 1/8 inch in length, and are usually born in
clusters.
Dodder germinates at or very near the soil surface starting in spring when soil
temperatures near 60 degrees F. Germinating seeds send up slender, twining
stems that coil around objects such as host plants. As dodder plants grow, they attach and
continually reattach to hosts. When
other suitable hosts are nearby, dodder shoots spread from host plant to host
plant, often forming a dense mat of intertwined stems.
The impact of dodder varies from moderate to severe reductions in growth of
host plants and, in some instances, death.
The greatest growth reduction occurs when dodder attaches to seedlings. Established host plants are usually not
killed by dodder, but can be weakened and thus more susceptible to other pests
and disease, including insect and nematode invasion.
Once an area is infested with dodder, it must be managed to prevent further
production of dodder seed. Isolate small
infestations and remove them by hand before seed is produced. Monitor larger infestations and mow, prune,
burn, or spray herbicides to prevent seed production. Dodder seedlings are difficult to find, but
if they are observed before they attach to hosts such as your petunias, remove
them by cultivation or by hand pulling. If
they have attached, prune the infected portion of the host plants at least 1/8
inch below the point of attachment.
Common ornamentals which are susceptible to dodder include chrysanthemum,
English ivy, fennel, impatiens, marjoram, mint, morning glory, periwinkle,
petunia, and summer savory. Susceptible
vegetables include asparagus, beet, carrot, eggplant, garlic, melon, onion,
pepper, potato, sweet potato, and tomato.
Keep a watchful eye on any wandering dodder tendrils that may be lurking in
your gardens and remove them immediately.
Your friendly hosts will thank you for it.