Common Broomrape

Domestic Programs Pest Evaluation. Arthur E. Miller, USDA-APHIS-PPQ, AERO, Raleigh, NC. October 6, 2003

Scientific name: Orobanche minor Smith (Orobanchaceae)

Physical description: OM is a fleshy, herbaceous, annual, parasitic plant that grows up to 22 inches tall. The stems are simple and yellow to straw-colored. The leaves are small triangular flaps, alternate to the stem. The roots are short, unbranched, fleshy, and attached to the roots of broadleaf hosts. The self-pollinating flowers are borne in an elongated terminal cluster. Petals are 1/2 inch long and snapdragon-like. Flower coloration is off-white to yellowish, with violet markings. The flowering period is short, starting about one week following emergence. The flowering period is March through May in southern Georgia.

The minute, easily dispersed seeds are prolifically produced and long-lived, some remaining viable for 10 years or more. OM is an obligate parasite. Under proper temperature and moisture conditions, the minute seed (0.5 mm) germinates in the presence of a stimulant from the root of a host plant. Upon host - parasitic contact, the tip of the radicle swells, producing a bulb-like haustorium. The swelling develops into a "spider" stage with reddish rootlets under ground, starting about January in southern Georgia.

Origin and North American Distribution: OM is native to the Middle East and North Africa. It has been introduced into several states. Infestations are currently known to exist in GA, NC, OR, PA, SC, VA, and VT.

Quarantines: OM is a Federal Noxious Weed.

Dispersal: This exotic invasive weed was probably introduced as a vetch seed contaminant and then the seeds were distributed mostly by mowers in southwestern Georgia. It was introduced into South Carolina by a plant collector and with clover seed into North Carolina and Virginia. Other means of dispersal can be soil, equipment, and visitor's shoes.

Control: Property managers and cooperators may use these strategies:

Cultural Control. Winter burning does not work as a stand alone treatment because OM will emerge from the roots of hosts such as catsear. Mowing does not appear to be very effective because seeds form rapidly close to the ground and additional stems arise from the haustorium. Up to 11 more buds have been observed on a common broomrape base in southern Georgia. When only a few OM are observed, these can be carefully dug (or pulled if dry) to reduce the spread and avoid new seeds going into the seed bank. Spot burning of dry plants is possible. Use of false hosts is ineffective if other host plants are present.

Chemical Control. During December through February, a 1% (38 ml/gal) glyphosate (Roundup) mixture is considered the most effective herbicide for roadsides and pecan groves in Georgia. This treatment is recommended for areas near or under crape myrtle, dogwood, and pecan trees during their dormant period. On turf and other grasses in Georgia, a mixture of .5 lb/a 2,4-D amine + .25 lb/a dicamba can be broadcast or spot treated to kill host plants. If 2,4-D amine is used alone as a spot treatment, utilize a 1% v/v solution (38 ml 2,4-D amine/gal of water) of the herbicide. For grass areas other than turf, e.g. highway right-of-ways, if 2,4-D amine is broadcast alone use the 1 lb/a rate. Florida betony, or rattlesnake weed, is problem in turf grass and a host of OM. Florida betony can be treated with Confront at 1 pint/a rate for broadcast or 16 ml/gal water for spot treatments.

A Burch Wetblade lawnmower was very effective when tested on heavily infested turf. Other equipment which has been tested includes DOT spray trucks, backpack sprayers, a John Deere Gator with sprayer, a Mule ATV, and a Ford tractor.

Biological Control. No agents are known. No insects have been found feeding on OM in GA. This strategy does not provide rapid response which is needed for small new weed infestations.

Economic impact: OM has a wide host range. There is concern that this weed may be spread from current infestations to crops such as legume forages and leafy green vegetables. Heavy infestations can cause crop failure. OM has not been observed on any of the major crops in southwestern Georgia, possibly due to asynchrony of life cycles which would differ in other counties and states. Flowers and vegetables in home gardens and ornamental plants are at risk.

Environmental impact: OM has a wide host range and can mutate. Untreated infested turf areas are made ugly with numerous large dead rust-colored plants. It may be parasitic on one or more threatened or endangered plant species.

Benefits of control: Protection of crops, yards, and endangered species in a wide range of climates in the U.S.