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Forestry, Wildlife and Natural Resource Management > FWNRM Blog > Posts > Tropical Soda Apple (Solanum viarum) Identification and Control

Tropical soda apple (TSA) was nearly eradicated across the state during a recent federally funded eradication program.  However, with termination of program funding, reports of this non-native invasive species are on the rise.  Tropical soda apple is of concern as it can form very dense infestations in open to semi-shady areas, especially in pastures where it can greatly reduce forage productivity.  Timely identification and control of this non-native, invasive Federal Noxious Weed will help prevent its spread.

How do I identify tropical soda apple? There are several species in the nightshade genus (Solanum)

that might be confused with tropical soda apple, but the most common look-a-like is horsenettle (S. carolinense).  Tropical soda apple looks a bit like horsenettle on steroids – the plants are bigger, the leaves are bigger, the thorns are bigger and the fruit is bigger.  Below are key features to help identify tropical soda apple.

figure1.tiff

  • Form: shallow rooted, spreading, thorny perennial shrub from 3 to 6 feet tall.

  • Leaves: 4 to 6 inches long and 2 to 6 inches wide, shallowly lobed with dense, sticky pubescence (velvety hair) on both sides, large prickles (1/2 to 1 inch) occur along the mid-veins.  Horsenettle leaves tend to be more narrow and the prickles are much smaller and only on veins on the bottom surface of the leaves.
  • Flowers:  May to August. Clusters of flowers with five white petals that are straight when first opened then curve back towards the stem, center is yellowish (Figure 1). The petals of horsenettle are fused and range from white to lavender.
  • figure2.tiffFruit: June to November.  Round (1-1.5 inches), smooth, mottled white and green (like watermelon rind) when immature (Figure 2), turning yellow when ripe. Occur in the leaf axils. Calyx (green leafy material at the top of the fruit where it attaches to the stem) covers very little of the fruit.  Horsenettle fruit is smaller (~0.5 inches) and the calyx reaches nearly a third of the way down the side of the fruit. 

  • figure3.tiffWhere does it grow?  Tropical soda apple is most commonly found in pastures, but is also found in open woods and other semi-shady areas.  It has been reported in scattered locations across the state and the southeast (Figure 3).  Reporting new locations of tropical soda apple will be very helpful in determining how rapidly it is spreading.  Reports can be made using the Early Detection and Distribution Mapping System (http://eddmaps.org) or the free SEEDN app (https://apps.bugwood.org/apps/seedn/) which makes reporting from the field a snap.  Reports can be marked private and will not be visible to the general public.
How is tropical soda apple spread?  Tropical soda apple fruit each contains several hundred seeds. The fruit is quite attractive to cattle and wildlife, which are the primary means of dispersal. Seed is also spread in contaminated hay, sod, manure and machinery.

How can I control tropical soda apple?   Tropical soda apple is very shallow rooted and small shrubs can be pulled with a sturdy pair of gloves (make sure they can withstand the thorns!).  When hand pulling, try to remove the lateral roots if possible. Cutting and mowing can be used to prevent seed formation, but will not control the plants and should be avoided after the plants have set fruit. 

What herbicides can I use to spray tropical soda apple? The best herbicide options for tropical soda apple in pastures are picloram + fluroxypyr, picloram + 2,4-D or aminopyralid + 2,4-D. In forests, the best options are aminopyralid, triclopyr and glyphosate. All of these herbicides benefit from the addition of a nonionic surfactant at 0.25% v/v.  Always read and follow the herbicide label. One treatment will not eradicate tropical soda apple and follow-up monitoring and retreatment is critical.  Treatments can be applied anytime during the late spring through early fall.

HerbicideHerbicide Active ingredient(s)Product RateRestricted useRecommended for:
SurmountPicloram + fluroxypyr2 pt/AYesPastures
Grazon P+DPicloram + 2,4-D 2 pt/AYesPastures
GrazonNext HLAminopyralid + 2,4-D1.5 pt/ANoPastures
Milestone VMAminopyralid7 fl oz/A or 0.5% v/vNo Forests*, ROWs
Remedy, Garlon 4Triclopyr ester1 qt/A or 2% v/vNoForests, ROWs
Accord ConcentrateGlyphosate3% v/vNoForests, ROWs

   *See label for specific forest information.

Prepared by: Nancy J. Loewenstein, Extension Specialist, School of Forestry and Wildlife Sciences and Stephen F. Enloe, former Extension Weed Specalsit, Department of Crop Soil, and Environmental Sciences, Auburn University.



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