S Nematology (Botany) Circular No. 48
COWPEA WITCHWEED, STRIGA GESNERIOIDES, A NEWI
ROOT-PARASITIC WEED INTRODUCED IN FLC
K. R. Langdon
Agric. : CF[sja pcerviced
Division o r Iht Industry
Y DISCO i 26 1987
RTDA University of Florida
The Division of Plant Industry was informed by United States Department of Agricul-
ture personnel on 23 January 1979 of positive identification of specimens of Striga
gesnerioides (Willd.) Vatke, collected in October 1978 near Bartow in Polk County.
The site was around old phosphate mining areas and was highly disturbed with a vari-
ety of weeds. The plants were parasitizing roots of hairy indigo, Indigofera hirsuta
L., and alyce clover, Alysicarpus vaginalis (L.) DC. Three subsequent locations
were reported in southwest Orange, southeast Lake, and northwest Osceola counties.
Cowpea witchweed is a small (3-18 inches tall), erect, annual, parasitic plant on
the roots of various plants. It has small scale-like leaves, green in the summer
and turning black in winter, contrasting with the brown, tan, or green of other plant
material. Flowers are reddish to purplish or white. Seeds are extremely small.
Striga gesnerioides flowering
parasitizing cowpea in Africa
Fig. 2. Striga gesnerioides dead specimens
in winter, parasitic on Indigofera hirsuta
in Florida (photo E. M. Collins)
DESCRIPTION: Striga gesnerioides (Willd.) Vatke (figs. 1,2) (synonym: S. oroban-
choides Benth.): A rigid, erect, annual, root-parasitic herb 0.75-5 dm (3-18 inches)
high, usually much branched from the base, more or less covered with short hairs or
almost glabrous; root tuberous, branches usually stout, angular, erect. Leaves scale-
* like, opposite or alternate, lanceolate, up to about 13 mm long, acute. Spikes ter-
minal, often as long as the branches themselves, usually much interrupted, but some-
times rather densely-flowered and scarcely interrupted; flowers opposite to alternate,
Contribution No. 193, Bureau of Nematology, P. O. Box 1269, Gainesville, FL 32602
Sessile; bracts lanceolate to broadly lanceolate, about 6 mm long, 1.5-2 mm broad,
acuminate, keeled, nearly glabrous or more or less pilose and ciliate; bracteoles
linear about 4 mm long. Calyx 7-13 mm long, somewhat scarious, short hairy or gla-
brous except the teeth, more or less irregularly 5-toothed, 5-nerved, splitting very
easily between the teeth; teeth lanceolate, acuminate, about 2 mm long, ciliate.
Corolla brownish red, rose, lavender, to purple, or white; tube 9-13 mm long, bent
and inflated"-B5ve the calyx, glabrous or minutely puberulous; limb 2-lipped; upper
lip shortly 2-lobed; lower lip deeply 3-lobed, lobes ovate, 3-5.5 mm long, 2.5-5 mm
broad, entire or slightly toothed at the apex, thin. Style about 4 mm long, per-
sistent. Capsule ovoid-oblong, 4.5-6 mm long, 2-3 mm broad, seeds very numerous
(50,000-500,000 per plant), 0.25-0.4mm long, thick, oblong, with heavy reticulations
running more or less diagonally, giving a twisted appearance; seeds sparkle with
colored highlights under high magnification.
Parasitic mostly on plants in the family Leguminosae, but also on some members of
Acanthaceae, Burseraceae, Convolvulaceae, Euphorbiaceae, Geraniaceae, Liliaceae,
Solanaceae, Vitaceae, and probably others. Native to Africa and India, newly estab-
lished in Florida.
HOSTS: Hosts listed in various literature are: Alysicarpus vaginalis (L.) DC.,
Arachis hypogaea L., Balsamea sp. (=Commiphora sp.), Cissus quadrangula L., Dalbergia
sp., Euphorbia abyssinica J. F. Gmel., Indigofera sp. (I. hirsuta L. in Florida),
Ipomoea filicaulis Blume, Jacquemontia tamnifolia Griseb., Lepidogathis sp., Merremia
tridentata (L.) Hallier f., Monsonia angustifolia E. Mey., Nicotiana tabacum L.,
rushes (Cyperaceae or Juncaceae?), Sansevieria sp., Tephrosia pedicillata Baker,
Vigna unguiculata (L.) Walp. There appear to be different strains or races of S.
gesnerioides, each parasitizing one or a few hosts, so that a particular population
probably would not attack all plants on the host list. Alysicarpus vaginalis and
Indigofera hirsuta are the only hosts definitely established at present for the
Florida population of S. gesnerioides.
DISCUSSION: Striga gesnerioides is often called cowpea witchweed (the preferred
vernacular name). It is also sometimes called tobacco witchweed or cowpea striga.
The very small seeds may be wind-dispersed, at least for short distances. Surveys
are being conducted to determine the extent of the current infestation. Yield re-
ductions of 50% were reported in Africa for cowpea infested with cowpea witchweed.
CONTROL: Control measures have yet to be worked out, but will probably involve one
or a combination of the following: trap cropping, herbicides, cultivation, fumiga-
tion, or seed germination stimulators. Seeds are reported to remain dormant and
viable in the soil for up to 20 years. These seeds normally germinate only when
stimulated by chemicals released by host roots. Certain plants, such as the nonhost
bambara, Voandzeia subterranea Thou., can stimulate germination of cowpea witchweed
seed without supporting growth. Also some plants which are hosts of one strain of
cowpea witchweed can stimulate germination of seeds of another strain incapable of
reproducing on this host. Much research remains to be done in this area.
Harvey, W. H., and O.W. Sonder. 1904. Flora capensis. 4(2):380. Hodges, Smith &
Reed, C. F. 1977. Economically important foreign weeds, USDA Agriculture Handbook
498. U. S. Government Printing Office, Washington. 746p.
Thiselton-Dyer, W. T. 1906. Flora of Tropical Africa. 4(2):402-403. Reeve,