Cooper’s broomrape or Desert broomrape[Orobanche cooperi (A. Gray) A.A. Heller][Bayer code: none][CDFA list: A] Photographs Map of Distribution

Branched broomrape [Orobanche ramosa L.][ORARA][CDFA list: A] Photographs

SYNONYMS:

• Cooper’s broomrape: desert broomrape, Orobanche ludoviciana Nutt. var. cooperi (A. Gray) Beck and var. latiloba Munz
• branched broomrape: hemp broomrape

GENERAL DESCRIPTION:Annual or perennial non-photosynthetic root parasites that lack chlorophyll and conspicuous foliage. Plants are visible above ground only while flowering and annual or perennial, depending on the life cycle of the host.

• Cooper’s broomrape is a widespread native of the Southwestern U.S., including California, and is not considered a weed in natural habitats. However, it can infest tomato fields and other crops in desert regions, especially the Coachella and Imperial valleys. Natural hosts are typically desert shrubs belonging to the family Asteraceae, and commonly include burro-weed [Ambrosia dumosa (A.Gray) Payne], Hymenoclea and Encelia species.
• branched broomrape is a worldwide noxious parasite of many crops and associated weeds. In California, it is especially problematic in tomato fields, and heavy infestations can severely damage crops. Introduced from Europe.

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SEEDLINGS:Not visible above ground. Host plant roots can have root nodules that resemble those caused by root-knot nematode or attached bullet-shaped to asparagus-like broomrape plants.

MATURE PLANT:Covered with very short, glandular hairs. Leaves reduced to alternate scales.

• Cooper’s broomrape: Dark purple, fleshy, stout, with a single main stem or a few thick branches from the base, to 40 cm tall. Scales rounded at the apex, 5-10 mm long.
• branched broomrape: Pale to bright yellow, with many slender branches from the base, to 60 cm tall. Scales few, deltoid-lanceolate, 7-8 mm long.

ROOTS and UNDERGROUND STRUCTURES:Roots modified to attach directly to host plant roots.

• Cooper’s broomrape: Root attachment usually branched, but sometimes rounded, coral-like.
• branched broomrape: Root attachment short, usually unbranched, fleshy.

FLOWERS:Two-lipped, sessile or on a short stalk with 2 small bracts, typically with more than 20 flowers per infloresence. Stigmas 2-lobed or shield-like. Stamens 4, included within flower tube.

• Cooper’s broomrape: January-May. Inflorescence dense, dark purple, 6-18 cm long, 4-5 cm wide. Calyx +/- equally 5-lobed. Corolla 18-32 mm long, lobes 5-10 mm long.
• branched broomrape: October-November. Infloresence open, mostly yellowish. Calyx 4-lobed, upper lobes deeply divided on top. Corolla 10-15 mm long, tube whitish, lobes and throat pale blue to lavender.

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FRUITS and SEEDS:Capsule 1-chambered, opens by 2 valves at the apex to release numerous seeds 0.3-0.5 mm long. Seeds angular-ovate, yellowish-brown, with a dull, net-like (reticulate) surface.

HABITAT:

• Cooper’s broomrape: Sandy flats and washes, creosote bush scrub, crop fields, especially tomatoes.
• branched broomrape: Ornamental and vegetable crop fields, especially tomato fields.

DISTRIBUTION:

• Cooper’s broomrape: Mojave, Sonoran deserts; to Utah, Arizona, Baja California. To 500 m (1640 ft).
• branched broomrape: San Francisco Bay region, northern San Joaquin Valley, eastern South Coast Ranges, South Coast Region. To 50 m (160 ft).

PROPAGATION/PHENOLOGY:Reproduces by seed. Seed disperses with human activities, farm machinery, water, and wind.

• Cooper’s broomrape: No information available.
• branched broomrape: Seed germination requires about a 1-2 week "preconditioning" period at a suitable temperature regime (10-30º C) with plentiful moisture, followed by a chemical signal from a nearby root of a host plant. Proximity of host root to seed is usually within a few millimeters. Light appears to inhibit germination. Seed can remain dormant in the soil seed bank for at least 7 years and probably to 12 years or more. Only a portion of the seed bank germinates in a given year. Plants can produce 600-2,000 seeds per capsule. Parasitism of host plant roots appears greatest when seed is buried about 10 cm deep.

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MANAGEMENT FAVORING/DISCOURAGING SURVIVAL:Hand pulling plants, plowing under trap crops before seed production, or burying seed with one deep inversion plowing can help control infestations.

SIMILAR SPECIES:There are several native broomrapes in California, a few of which are uncommon to rare, but only Cooper’s broomrape occurs in the Mojave and Sonoran deserts (excluding desert mountains) and is a weed of vegetable crops. Unlike branched broomrape, native broomrapes have 5-lobed calyces.

CONTROL METHODS

Prevention and control: Orobanche ramosa is a serious threat to tomato production in California. Plant only certified seed and clean nursery stock to avoid introducing Orobanche species into production fields. Orobanche seeds are very small and easily separated from most crop seed grown in California. However, seed are also easily transported on contaminated equipment and in irrigation or flood water, Additionally, O. ramosa may survive on several hosts other than tomato including many common agricultural weeds. Surveys of infested or previously infested fields should include surrounding field borders that may act as a refuge. Seed may survive in the soil for many years, so repeated annual monitoring is essential. Strategies for dealing with infestations include hand removing plants before flowering, planting trap crops that will induce Orobanche to germinate followed by cultivation before flowering and soil fumigation. Heavily infested fields may need to be rotated to non-susceptible crops for at least two years.

References:
Dhanapal, G. N., P. C. Struik, M. Udayakumar, and J. M. Timmermans. 1996. Management of Broomrape (Orobanche spp.) - A review. Journal of Agronomy and Crop Science 175:335-359.
Foy, C. L., R. Jain, and R. Jacobsohn. 1989. Recent approaches for chemical control of broomrape (Orobanche spp.). Reviews in Weed Science 4:123-152.
Holm, L., J. Doll, E. Holm, J. Pancho, and J. Herberger. 1997. Obligate parasitic weeds: Orobanche ramosa L., and Orobanche minor Sm. In 'World Weeds: Natural Histories and Distribution' pp. 511-530 (John Wiley & Sons Inc: New York).
Mitich, L. W. 1993. Orobanche-The Broomrapes. Weed Technology 7:532-535.
Musselman, L. J. 1980. The biology of Striga, Orobanche, and other root-parasitic weeds. Annual Reviews of Phytopathology 18:463-489.
Stout, G. L. 1938. A recurrence of broomrape (Orobanche ramosa L.) on tomato plants in California. California Department of Agriculture Bulletin 27(2):166-171.

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