Plant: Tropical soda apple (Solanum Viarum) is a Federally listed noxious weed native to Argentina and Brazil.
Identification: Upright to leaning, multi-branched, perennial shrub can grow 3 to 6 ft tall. It is covered with velvety hair and broad-based white to yellow thorns. Leaves, resembling that of the northern red oak, are deeply lobed and alternate, 4 to 8 inches long and 2 to 6 inches wide. Leaves are dark green with whitish midveins above and below, lighter green with netted veins. In Alabama, flowers appear from May to August having small terminal clusters of 5-petaled white flowers and yellow to white fused stamens projecting from the center. From June to November, flowers produce whitish, mottled green spherical fruit, 1 to 1.5 inches wide that ripens to yellow. In most southern locations, however, the fruit remains green over the winter. Each sweet smelling, but poisonous fruit can produce 200 to 400 reddish-brown seeds. Tropical soda apple resembles horsenettle (Solanum carolinense).
Ecology: Tropical soda apple occurs on open to semi-shady sites. It can reach maturity from seed within 105 days. Tropical soda apple spreads rapidly by livestock-dispersed and wildlife-dispersed seeds as well as seed-contaminated hay, sod, and machinery.
Herbicide Control: Apply anytime during flowering before the fruit appears, a 60+% active ingredient of triclopyr (Garlon 4, Remedy, or Tahoe 4E) or a 42+% active ingredient of imazapyr (Arsenal AC, Vanquish, or Polaris AC) or a 24.4% active ingredient of picloram (Tordon K) as a 2% solution (8 ounces per 3-gal. mix) in water with a surfactant (methylated seed oil, basal oil, or vegetable oil) at a 1% solution (4 ounces per 3-gal mix). Alternatively, apply a 41% active ingredient of glyphosate (Accord, Razor, or Roundup Original) as a 3% solution (12 ounces per 3-gal. mix) or a 40.6% active ingredient of aminopyralid (Milestone VM) as a 0.5% solution (2 ounces per 3-gal mix) or a 10.2% active ingredient of picloram (Tordon 101 or Grazon P+D) as a 4% solution (1 pint per 3-gal mix) in water with a surfactant at a 1% solution. Thoroughly wet all leaves and stems. Mowing can be used to stop fruit production. Herbicide applications should be made 50 to 60 days after mowing to allow for adequate regrowth. Collect and destroy fruit to prevent reestablishment.
Warning: The active ingredients of imazapyr, aminopyralid, and picloram can injure or kill plants with roots in the affected area. Always read and follow label directions carefully.
Source: (A Field Guide for the Identification of, A Management Guide for) Invasive Plants in Southern Forests, James H. Miller, USDA Forest Service, 2010. Photo Credit: J. Jeffrey Mullahey, University of Florida, ForestryImages.Org