Death Knell for the "The Plant from Hell"

July 2002
Gary Mikulecky - Highlands County Extension, Director/Livestock Agent

The Tropical Soda Apple, often called "The Plant from Hell", may obtain a fatal viral infection thanks to the work of Raghavan Charudattan, professor of plant pathology with University of Florida's Institute of Food and Agricultural Sciences. Charudattan's research has shown promise using tobacco mild green mosaic virus to control tropical soda apple (TSA). Preliminary tests have achieved a 97% kill rate. Additional test sites on producer pastures are planned for this summer. Testing will also be done on tobacco and pepper plants that are known to be susceptible to the virus. Additional testing will be done on weeds and cultivated plants to determine if it is safe for use in Florida range conditions.

This virus is inexpensively and easily applied with a boom or backpack sprayer. It is effective in a wide range of temperatures and our year-around-growing conditions. Charudattan plans to establish a pilot production system to demonstrate how easily and inexpensively the bioherbicide can be produced. The system consists of inoculating susceptible tobacco plants with the virus, harvesting the mature leaves, freeze drying leaves, and grinding them into a fine powder.

Current control methods include mowing and herbicides. TSA needs to be 16-24 inches tall and actively growing when herbicides are applied. If plants are taller than that; mow them and spray when plants reach desired height. Recommended spray is 1 quart of Remedy in 60-65 gallons of water per acre. It will be necessary to repeat applications.

Spot treatment will be needed in hammocks, cypress heads and other native areas to control TSA seed production. Wildlife and cattle will spread these seeds to other areas. The recommended herbicides for these areas are Weedone CB, 2.8% Roundup solution or a 1% Remedy solution. The weed and grasses will be killed by the roundup - so use it cautiously. Weedone CB and Remedy will not harm grasses.

TSA has become a serious broadleaf perennial weed problem in Southern Florida. The plant has unpalatable foliage but wildlife and livestock risk getting stuck by the many spines to obtain the tasty fruits. The fruits are yellow and 1-1.5 inches in diameter. Each fruit contains 200-400 seeds. Each plant can produce 40,000 to 50,000 viable seeds per year. Fruit production occurs throughout the year. Wildlife and cows will consume the fruit and spread the seeds through their manure. For cattle, it takes approximately 16 days for the seeds to pass through the digestive system, but the seeds are not viable after six days. This is the reasoning behind the seven-day TSA free quarantine for cattle. Hay and sod from infected pastures and composted cow manure also contribute to the spread of TSA. TSA plants can grow from seed or feeder roots of existing plants. This extensive root system grows a few inches under ground and extends 3-6 feet from the crown of the plant. More testing remains but this bioherbicide looks promising.

References

  • Tropical Soda Apple (Solanum varum Dunal) in Florida, SS-AGR-50, J. Jeffrey Mullahey and Daniel L. Colvin.
  • Adapted from Unleashing A Virus To Control "The Plant From Hell", Daily University News, Chuck Woods.

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