Alfalfa Field

Pests

Dodder

DESCRIPTION OF THE PESTS

Dodder is a twining yellow or orange plant sometimes tinged with purple or red. Occasionally it is almost white. The stems can be very thin and thread-like or relatively stout.

Dodder parasitizes various kinds of wild and cultivated plants, and is especially destructive to alfalfa, lespedeza, flax, clover and potatoes. Ornamentals attacked included chrysanthemum, dahlia, helenium, Virginia-creeper, trumpet-vine, English ivy and petunias. Dodder is particularly troublesome where alfalfa, clover and onion are grown for seed because dodder seed is difficult to remove from the desired seed crop and can be spread with infested seed. Its water, minerals and carbohydrates are absorbed from the host through haustoria (an outgrowth of stem, root, or hyphae of certain parasitic plants which serves to draw food from the host plant), that penetrate the host's tissue. In dodder the haustoria are modified adventitious roots.

Dodder is said (Wilson, et al.) to contain some chlorophyll in the buds, fruits and stems, but the amount of food manufactured in this tissue is of little significance to the survival of the plant.

The flowers are numerous, white, pink or yellowish, small (2 to 4 mm long depending on species), and can be borne in tight balls or in a loose cluster (again depending on species). Flowers normally appear from early June to the end of the growing season. The fruit is about 1/8^th inch in diameter, with thin papery walls and contain 1 to 4 seeds. The seeds are yellow to brown or black, nearly round and have a fine rough surface with one round and two flat sides.

DAMAGE

Dodder produces seed that drops to the ground and germinate the next growing season if a suitable host is present. If no suitable host is present, the seed may remain dormant for five years. Smoothseed Alfalfa Dodder ((Cuscuta approximata Bab. Var. urceolata (Kunze) Yuncker) is reported to produce over 16,000 seeds per plant. "The seed viability times range from 20 to over 60 years and germination can be delayed for years. The seeds can travel by water along irrigation ditches. Moist soil and sunlight is required for germination. The seeds can germinate without a host plant, unlike the seeds of most parasitic plants."

Dodder seedlings must attach to a suitable host within a few days of germinating or they die. The young seedling is sensitive to touch and yellowish stem gropes in the air until it makes contact with a plant. The contact is made firm by one or more coils about the stem. If this plant happens to contain foods suitable to the dodder then a secondary stimulus is aroused which causes root-like branches (haustoria) to form and penetrate the stem. The basal part of the parasite soon shrivels away so that no soil connection exists.

Dodder

Advanced spreading of dodder