Clover (Trifolium spp.)-Clover Broom-rape

Cause Orobanche minor (clover broom-rape) is a federally listed noxious weed that has quarantine significance to many of Oregon's trading partners.

From 1923 to 1997, there have been 6 reports of clover broom-rape in Oregon. In 1998, clover broom-rape was identified in a single field. In 2000, clover broom-rape was found in 15 fields in northwestern Oregon. Native species of broom-rape can be found in all parts of Oregon.

Clover broom-rape reproduces and spreads only by seed. One broom-rape plant produces up to 500,000 dust-like seeds that may be dispersed by wind, machinery, contaminated seed crops, animals, or clothing. Flowering plants that are hand-pulled may still mature and produce viable seed. Seed can remain dormant in the soil for 10 years or more. After germination, clover broom-rape attaches to and penetrates the root of the host plant, disrupting nutrient and water transport in the host root system. Parasitism by clover broom-rape may reduce host crop yield, and, in heavy infestations, kill the host plant.

Red clover is currently the only host in Oregon but greenhouse studies have identified several other weed and crop species that can be clover broom-rape hosts. Clover broom-rape germinated and attached to nasturtium, arrowleaf clover, subterranean clover, white clover, sweet pea, lettuce, snap bean, sunflower, and carrot.

Symptoms Annual or perennial, yellowish, brown or purplish root parasites that lack chlorophyll. Stems are simple or branched and fleshy and bare scale-like leaves. Flowers racemose or solitary, white, yellow-white, or slightly purple, resembling a snapdragon.