Tropical Soda Apple: History, Biology, Impacts, and Management
Topical Soda Apple is originally from southeastern Brazil, northeastern Argentina, Paraguay, and Uruguay. However, since it is not considered as a species of concern in these countries, it is probably regulated by natural enemies that don't exist in the USA. This South American native was first identified in 1988 in Glades County, Florida. By 1994, this plant was placed on the Florida Noxious Weed List, and in 1995 on the Federal Noxious Weed List. As of 1999, it has been listed as a Category I invasive species by the Florida Exotic Pest Plant Council. Category I plants are defined as “non-native species that have invaded natural areas, and are displacing native plants or are disrupting natural community structure and function”.
This perennial shrub has velvety, oak-shaped leaves with thorns along the veins and petioles. The green/yellow fruit will keep its color through the winter months. Tropical soda apple can be found in ditch banks, oak hammocks, swamps, cypress heads, and cattle chutes.
A plant produces about 200-400 seeds per fruit and 125 berries per plant (about 45,000 seeds with 70%viability). Cattle, raccoons, deer, and feral pigs are excellent vectors for spreading the seed. While in the animals’ digestive system, the seeds are scarified, thus promoting germination in their feces. Dissemination also occurs through harvesting seed or hay (bahia grass, bermudagrass, clover, etc.) in infested areas.
Since its first identification in 1988, tropical soda apple has spread to more than 500,000 acres of pastures and pine-lands throughout Florida. The swift spread of tropical soda apple throughout the southeast occurred accidentally through the cattle industry. The number of infested acres in Georgia, Mississippi, and Alabama was directly related to the number of cattle imported from Florida.
Impacts and Threat
Both economic (from cattle farming) and ecological degradation have resulted from the infestation of tropical soda apple. This plant has become a problem for ranchers because it quickly covers entire pastures and is replacing forage crops. In severe cases of tropical soda apple, the productivity of infested pastures may be reduced by more than 90%. This has reduced livestock carrying capacities of pastures and, in dense stands, has invaded shaded areas used by cattle during warm seasons. This lack of available shade has resulted in heat stress to cattle and an estimated $2 million loss in beef sales.
In addition to causing economic problems, tropical soda apple reduces the biological diversity in natural areas by displacing native plants and disrupting the ecological integrity.
Recommendations for controlling this invasive plant will vary depending on the severityof infestation. For individual plant control, the Mississippi Department of Agriculture (MDA) suggests removal of all tropical soda apple plants (including fruits and roots) and complete destruction by burning. For more severe infestations, herbicide application or biological control should be considered.
For a few sparse occurrences of tropical soda apple, University of Florida suggests spot treatments of either Milestone or GrazonNext HL herbicides. However, if the infestation is dense, control recommendations will require further management. Landowners should mow all tropical soda apple plants to about 3-4 inches in height to prevent fruit/seed production. About 40 to 60 days after mowing (or at flower stage), a broadcast spray of both Milestone and GrazonNext HL herbicides to plants 12 to 15 inches tall should be implemented for best results. Be sure to monitor infested and adjacent areas monthly and spray all new growth with broadcast or spot treatments as suggested above. Another option is to use a triclopyr herbicide.
One of the natural enemies of tropical soda apple is the South American native known as the South American leaf beetle, Gratiana boliviana. In April 2002, the Technical Advisory Group for Biological Control Agents of Weeds (TAG) approved this beetle for field release in Florida. The beetle has a high level of specificity for tropical soda apple. It reduces the overall fitness of the plant, therefore making the plant less competitive with other plants.
Another option for biocontrol of tropical soda apple is the Tobacco Mild Green MosaicVirus (TMGMV). This virus is native to Florida and causes a rapid, systemic, hypersensitive response in tropical soda apple plants within 7-14 days of inoculation. This method of control is highly effective and only requires inoculation of a few leaves per plant to produce up to 99% control. Although there may be a risk to tobacco and peppers if applied nearby, dissemination is unlikely.