Leaflets are wide or wider than long and usually have a reddish spot in the middle, spiny stipules with spiny lobes, 1-5 flowers, and a legume that is spirally coiled (4-7 coils) with a double row of curved spines.
Scarification of seed is beneficial for germination (Cross 1931). Seed viability did not drop much over 4 years of cold storage (Lewis 1958).
The annual Medicagos are believed to be self-fertilized (USDA 1948). A native of the Old World that is now a widespread weed found throughout most of Louisiana and the eastern half of Texas. .
Noxious tropical invader bears thorns, seedy fruit
Being new to an area can prove challenging for the recently arrived. Identifying where things are and how to access the needed resources is a bit intimidating for some.
Others, however, arrive on the scene with an aggressive stance and posture. Their antagonistic and lordly countenance immediately notifies all in the area conflict is at hand.
The latter is the case when it comes to tropical soda apple, an invasive exotic weed. To date there has been five reported varieties in Florida.
This exotic weed is native to Mexico and countries in Central and South America. It was first reported in Glades County, Florida, in 1988 and may have arrived in livestock imported from Central America.
The ensuing years has seen TSA spread to Georgia, Alabama, Louisiana, Texas, Mississippi, Tennessee, North Carolina, and South Carolina.
This plant is exceptionally vigorous and will become quickly established is sunny and partially shaded areas, preferring disturbed soils. Tropical soda apple is a perennial pest capable of springtime regrowth in Leon County.
Tropical soda apple is in the Solanaceae plant family, which includes tomatoes, potatoes, eggplant, horse-nettles, and night shade. Immature plants are often confused with horse-nettles, which display copious quantities of thorns and barbs.
This exotic pest can easily be identified by its fruit. Developing TSA fruit looks like a tiny watermelon with green and white stripes. Mature fruit turns yellow.
Each fruit contains 200 to 400 seed, with about a 75 percent germination rate. Each plant has the potential to produce over 10,000 viable seed ready to colonize new ground.
Livestock and wildlife, especially deer and raccoons, are attracted to the TSA’s fruit with its tiny seed. Deer and raccoons have the dexterity to negotiate the thorns, and cattle will nibble on the fruit of dormant plants.
Undigested seeds are conveniently deposited to wherever the animal travels. The seed are delivered with an immediately available nutrient base of animal manure to encourage growth.
This weed is a major problem in pastures and conservation areas. Negative impacts of TSA include reduction of cattle stocking rates, competition with native plants, and the costs associated with its control.
Dense thickets of this noxious weed can disrupt the movement patterns of wildlife, further changing the natural balance of an area.
Several herbicide control protocols have been developed to help alleviate this invasive situation. The latest control method utilized in south and central Florida is biological. The tropical soda apple leaf beetle, Gratiana boliviana Spaeth, was discovered in Paraguay and imported into the United States to study as a potential biological control agent. Because Gratiana boliviana fed and survived only on TSA, field release trials were approved in 2003.
A multi-agency program supported the rearing, distribution, and release of more than 250,000 beetles across Florida from 2003 to 2011. Gratiana boliviana was also released in Texas, Alabama, and Georgia, but establishment has not been confirmed.
Feeding damage by larvae and adults of Gratiana boliviana is characterized by a distinctive “shotgun-birdshot-hole” pattern on leaves. This damage reduces the photosynthetic area of the leaves and creates wounds which may facilitate attack by plant diseases.
These cumulative stresses hinder the growth and reproduction of tropical soda apple. By reducing the competitive ability of the weed, Gratiana boliviana indirectly facilitates the recovery of pasture grasses and native vegetation.
Tame TSA through effective horticultural practices. Even aggressive recently arrived bullies can be controlled, but it takes a concerted effort.