Small broomrape, a holoparasitic weed, was recently introduced to the Pacific Northwest and contaminates a limited number of red clover fields in Oregon. Greenhouse and field studies were conducted to evaluate small broomrape response to common crop and weed species in the Pacific Northwest, and to evaluate a quick-screening method for plant species response to the parasite. In greenhouse studies, plants were grown in a hydroponic polyethylene bag system to allow for continuous visibility of their roots and monitoring of small broomrape seed germination and tubercle development. Results of the greenhouse study were validated in a field contaminated with small broomrape. In the greenhouse polyethylene bag study, small broomrape germinated and tubercles developed on alfalfa, arrowleaf clover, carrot, celery, crimson clover, lettuce, prickly lettuce, red clover, spotted catsear, subterranean clover, white clover, and wild carrot. Small broomrape germinated but did not develop tubercles when grown with barley, birdsfoot trefoil, common vetch, creeping bentgrass, cucumber, field corn, red fescue, flax, Italian ryegrass, nasturtium, oats, orchardgrass, perennial ryegrass, snap bean, sugar pea, sunflower, sweet corn, tall fescue, tomato, and wheat. In the field study, tubercles developed on alfalfa, arrowleaf clover, common vetch, crimson clover, red clover, subterranean clover, and white clover, but small broomrape flower stalks did not emerge in arrowleaf clover or crimson clover. Common vetch was a host for small broomrape in the field study but not in the hydroponic polyethylene bag system, thus, caution is warranted in using the quick screening method to elucidate potential small broomrape host species.
Nomenclature: Curly dock, Rumex crispus L. RUMCR; prickly lettuce, Lactuca serriola L. LACSE; spotted catsear, Hypochaeris radicata L. HYPRA; wild carrot, Daucus carota L. DAUCA; alfalfa, Medicago sativa L. MEDSA; arrowleaf clover, Trifolium vesciculosum Savi. TRFVE; barley, Hordeum vulgare L. HORVX; birdsfoot trefoil, Lotus corniculatus L. LOTCO; carrot, Daucus carota L. DAUCS; celery, Apium graveolens L. AOUGD; common vetch, Vicia sativa L. VICSA; creeping bentgrass, Agrostis stolonifera L. AGSTE; crimson clover, Trifolium incarnatum L. TRFIN; cucumber, Cucumis sativus L. CUMSA; field corn, Zea mays L. ZEAMA; flax, Linum usitatissimum L. LIUUT; Italian ryegrass, Lolium multiflorum Lam. LOLMU; lettuce, Lactuca sativa L. LACSA; nasturtium, Tropaeolum majus L. TOPMA; oats, Avena sativa L. AVESA; orchardgrass, Dactylis glomerata L. DACGL; perennial ryegrass, Lolium perenne L. LOLPE; red clover, Trifolium pratense L. TRFPR; red fescue, Festuca rubra L. FESRU; small broomrape, Orobanche minor Sm. ORAMI;
snap bean, Phaseolus vulgaris L. PHSVN; subterranean clover, Trifolium subterraneum L. TRFSU; sugar pea, Pisium sativum L. PIBST; sunflower, Helianthus annuus L. HELAN