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Problem
Tropical soda apple, Solanum viarum Dunal is a perennial shrub (Figure 1). It is native to Brazil and Argentina, but has
become a weed in other areas of South America and in Africa, India, Nepal, West Indies, Honduras, and Mexico and the
U.S. The primary means of dispersal of tropical soda apple in the U.S. is livestock and wildlife, such as raccoons, deer,
feral hogs, and birds feeding on fruits. Mullahey et al. (1993) reported tropical soda apple foliage is unpalatable to
livestock, although cattle will eat the mature fruit. Scarification of seeds by digestive systems of livestock and wildlife
seems to promote germination. Intra- and inter-county and state movement of livestock that have recently consumed
tropical soda apple fruit are the primary vectors for long distance spread. However, contaminated equipment, hay, seeds,
composted manure, and sod may also serve as means of dispersal. Once established in an area, wildlife may continue
the short range spread of tropical soda apple. Tropical soda apple is an alternate host for numerous pathogens that are
diseases of eggplant, peppers, potatoes, tomatoes, etc. Tropical soda apple cost the cattle business over $11 million in
1994. Damage to croplands, forestlands, and natural habitats and the cost of control of currently infested areas is difficult
to determine, but tropical soda apple has the potential to become a major problem throughout the southern U.S. In order
to detect and prevent further spread of this pernicious weed in the U.S., the Extension Service and the Departments of
Agriculture in several states in the Southern U.S. and the U.S. Department of Agriculture have initiated an education and
notification campaign on the potential weed problem of tropical soda apple. Early detection persistent monitoring
populations is paramount to contain the threat of this weed which has the potential to infest millions of acres of pastures,
crops, forests, and natural areas in the U.S.
Regulations
Tropical soda apple is a Noxious weed in the U. S. It is a state Noxious weed in Florida, Mississippi, and Texas. Cattle
from areas infested with tropical soda apple must be quarantined prior to movement into several states.
Tropical Soda Apple (
Solanum viarum
Dunal)
Charles T. Bryson, USDA-ARS (Retired), Southern Weed Science Lab, Stoneville, MS
John D. Byrd, Jr., Extension/Research Professor, Mississippi State University
Randy Westbrooks, Invasive Species Specialist (Retired), U.S. Geological Survey
Victor Maddox, Senior Research Associate, Mississippi State University
Description
Vegetative Growth
Mature plants of tropical soda apple are 3 to 6 feet tall and can be as wide. Plants are armed on the leaves, stems,
pedicles, petioles, and calyxes with broad based white to yellowish thorn-like prickles up to ¾ inch long (Figure 2). The
leaves and stems are pubescent. Stems are green. Tropical soda apple is closely related to Carolina horsenettle
(Solanum carolinense L.), which rarely exceeds 3 feet tall and can have green or purple stems.
Flowering
Flowers are white with five petals that curve backwards and white cream colored stamens that surround the single pistil.
Carolina horsenettle flower petals are not curved backwards and can be either white or purple.
Fruit
Immature fruits are mottled whitish to light green and dark green, like a watermelon (Figure 3). Mature fruits are smooth,
round, and ¾ to 1 ¼ inches in diameter (Figure 3) with a leathery yellow skin surrounding a thin-layered, pale green,
scented pulp and 180 to 420 flattened, reddish brown seeds. Each plant is capable of producing 200 or more fruit per
year. Carolina horsenettle fruits are glossy green (immature), but turn yellow at maturity, 1/2 to 3/4 inch diameter and
typically occur in clusters.
Introduction
Fig. 2. Tropical soda apple leaves with
prickles and immature fruit.
Fig. 1. Tropical soda apple plant in pasture. Fig. 3. Tropical soda apple with mature
(yellow) and immature (green mottled) fruit.
Distribution
U.S.
The first known collection of tropical soda apple in the U.S. was from Glades County, Florida in 1988. Because of its rapid
population explosion in Florida and the concerns of livestock producers, tropical soda apple was placed on the Florida
Noxious Weed List in late February 1994 and was placed on the Federal Noxious list in 1995. It currently is escaped from
North Carolina to Tennessee and Louisiana in the southeastern United States and Pennsylvania in the northeastern
United States. Tropical Soda Apple occurs in most of the counties in Florida. It was found in Mississippi in October 1993.
It has been confirmed at 20 sites in 10 Mississippi counties.
Mid-South
Tropical soda apple has been reported in all Mid-South States, except Arkansas.
Control Methods
Biological
None known.
Chemical
See Table 1. Aminopyralid, triclopyr, and hexazinone are
effective for control of emerged tropical soda apple when
applied at recommended rates. If plants have been
established long enough to release seed, the site should be
frequently inspected and newly emerged seedlings treated.
Aminopyralid and hexazinone have longer residual than
triclopyr.
Mechanical
Since plants have thorns, use caution if removing by hand.
Plants can regenerate from roots, so complete removal is
necessary. To prevent tropical sold apple spread within a
farm or community, steps should be taken to minimize seed
production. Mowing is an effective practice to prevent seed
production, even after flowering has started, although plant
regrowth will occur and the practice must be repeated when
plants start flowering again. Plants with mature fruit should
be cut, piled, and burned to destroy seed viability, or buried
more than 3 feet deep.
Cultural
The only cultural control is sanitation. Collect fruit prior to
maturity and dispose by burning or cooking. Quarantine
livestock at least 7 days in an area with no tropical soda
apple prior to movement to new uninfested locations.
John Byrd, Extension/Research Professor
Victor Maddox, Senior Research Associate
Mississippi State University
Box 9555, Mississippi State, MS 39762-9555 Ph.
(662) 325-2311
jbyrd@pss.msstate.edu
vmaddox@pss.msstate.edu
More Information
Habitat
Since its introduction into the U.S., tropical soda apple has spread rapidly, and currently infests an estimated one million
acres of improved pastures, citrus groves, sugar cane fields, ditches, vegetable crops, sod farms, forestlands (oak ham-
mocks and cypress heads), natural areas, etc. in Alabama, Florida, Georgia, and Mississippi. Although it can be a threat
to a variety of habitat, it tends to be most problematic in pastures and surrounding woodlands in the Mid-South.
Dispersal and Spread
The primary means of dispersal of tropical soda apple in the U.S. is livestock and wildlife, such as raccoons, deer, feral
hogs, and birds feeding on fruits.
Mullahey, J.J., J.A. Cornell, and D.L. Colvin. 1993. Tropical soda apple (Solanum viarum) control. Weed Technol. 7:723-727.
Mullahey, J.J., M. Nee, R.P. Wunderlin, and K.R. Delaney. 1993. Tropical soda apple (Solanum viarum): a weed threat to
subtropical regions. Weed Technol. 7:783-786.
