Journal of Undergraduate Research
Volume 1, Issue 7 - April 2000

Simulation of Rodeo Overspray Damage to Maidencane, Three Square, and Soft-stem

Nora Fosman

ABSTRACT

As urban development encroaches upon the Everglades important wetland areas are lost to neighborhoods and shopping centers. In an effort to mitigate the loss of these important areas the State government has implemented laws for protection and restoration of wetlands. Because these natural areas have been invaded with exotic plant species over many decades, restoration is especially challenging. Once the area has been cleared and replanted, the exotics must be kept in check in order for the newly planted natives to establish. One of the most resilient exotics is Torpedograss, which was originally introduced to Florida as a promising crop for foraging cattle. Torpedograss has no wildlife value and chokes out vegetation that does. Three plants were selected based on their wildlife value in order to test their possible resistance to the non-selective herbicide Rodeo. Rodeo damage was evaluated on maidencane (Panicum hemitomon Schult.), three-square (Scirpus americanus Pers.), and soft-rush (Juncus effusus L.) planted under conditions known to provide for optimum growth. Rodeo was applied 0.25, 0.50, and 1.0 percent concentrated solutions to plants 12 weeks after initial planting. Field studies were conducted at the University of Florida Research and Education Facility in Fort Lauderdale, FL beginning in August of 1998.

INTRODUCTION

Florida has lost nearly one-half of its 11 million acres of wetlands to both agricultural drainage and urban sprawl (U.S. Geological Survey, 1999). The state protects its remaining wetlands by regulating development in these areas as well as restoring areas that have been impacted by it. Many of these restoration sites in south Florida have been inundated for decades by stands of Melalueca and torpedograss. Although both of these plants have been designated by the Florida Exotic Pest Plant Council as highly invasive, Melalueca has been successfully eradicated from these sites by simply bulldozing the trees. (1997)

Figure 1. Melalueca removal from wetlands.

Any volunteers that emerge after the initial clean up are treated with herbicide. Torpedograss however, is not so easily eradicated.

Due to its unique physiology, torpedo grass has proven to be a most resilient pest. It readily regrows from dormant buds located along its rhizome. If the entire rhizome is not removed or killed, the plant will survive and reproduce (Sutton, 1996). These rhizomes are extensive, some have been found to exceed seven meters in length (Holm, et al, 1977). For this reason, it is rarely eradicated with just one application of herbicide. Because of this, interval spraying is the preferred method of control. Since Rodeo is a nonselective herbicide, studies were conducted to determine the effect of Rodeo concentration on non-target plants, which may be affected by overspray.

Torpedograss is a noxious weed of both natural and restored wetlands in Florida. Eradication programs have been implemented by state governmental agencies to control this pest in lakes, wetlands, and canals. Torpedo grass chokes out native emerged vegetation and clogs drainage canals that are essential throughout south Florida (Schmitz et al. 1997). Since multiple applications of Rodeo have proven effective in controlling torpedograss (Smith and Langeland, 1998) it is important to find native species that exhibit similar resistance to Rodeo, since overspray of desirable species is inevitable in treatment programs.

Plant species were selected on the basis of the benefits that they provide to the environment as well as wildlife. All three species provide food, shelter, and nesting for wildlife, as well as shoreline stabilization. Maidencane is a native aquatic grass that is physiologically similar to torpedo grass. Three-square and soft rushes are native rushes of Florida's wetlands (Figures 2A, B, and C).

Figure 2a. Maidencane (Panicum hemitomon Schult.). Maidencane is a native aquatic grass similar to torpedograss that provides food, shelter, and nesting for wildlife, and provides shoreline stabilization.

Figure 2b. Three-Sqaure (Scirpus americanus Pers.). Three-Square is one of the smaller bullrushes that provides food, shelter, and nesting for wildlife, and provides shoreline stabilization.

Figure 2c. Soft-stem (Juncus effuses L.). One of the most common rushes that provides food, shelter, and nesting for wildlife, and provides shoreline stabilization.

MATERIALS AND METHODS

Florida has lost nearly o Field studies were conducted at the University of Florida Fort Lauderdale Research and Education Center beginning in September of 1998. Plants were grown in sand in 2- gallon pots without holes on a runway under overhead irrigation (Figure 3). Each pot was filled with 3.5 inches of sand, Osmocote plus fertilizer was then placed in the pot. Three inches of sand was placed over the top of the fertilizer, then each pot was planted with one well-developed Maidencane rhizome section with several nodes, and one culm with roots for three-square, and one to three culms with roots for soft-rush. Maidencane was planted with 40 grams of Osmocote plus and Three-square and Soft-stem were each planted with 16 grams of Osmocote plus. Plants were grown for 12 weeks on a runway with overhead irrigation.

Figure 3. Experimental plants prior to treatment.

Experimental design was a randomized complete block with a factorial arrangement of treatments, including an augmented non-treated control. Each treatment was replicated four times. Rodeo was applied at 0.25, 0.50, and 1.00 percent concentrated solutions with a nonionic surfactant. Plants were sprayed to wet with a backpack sprayer (Figure 4). Treatment 1 was harvested for initial dry weight. The remaining treatments were allowed to grow for an additional 4 weeks and were visually evaluated at weekly intervals for percentage of green. Rating scheme was 100 (entire plant green) to 0 (plant with no green) (Figures 5A, B, and C).

Figure 4. Application of Rodeo herbicide.

Figure 5a.

Figure 5b.

Figure 5c.

All treatments were harvested at the end of 4 weeks for dry weight determination. Culms were counted for Three-square and Soft-stem before shoots were separated from roots. Roots and shoots were placed in labeled paper bags, dried for one week, and weighed. Plant growth was determined by dry weight to determine the efficacy of this aquatic herbicide.

RESULTS AND DISCUSSION

After harvesting, the roots of the plants were rinsed of all sand and Osmocote. Upon visually comparing the roots of the control plants with those of the treatments, it was observed that the damage to the roots was not as significant as the damage to the shoots (Figures 6A, B, and C). However, upon comparing the dry weights of the roots, an obvious difference was noted.

Figure 6a.

Figure 6b.

Figure 6c.

Maidencane shoots showed about 50% damaged with 0.25 percent concentrated solution of Rodeo. Higher rates resulted in more damage to the shoots. Herbicide damage to soft rush was intermediate to that of the three plants studied. Three-square showed the most resistance to the Rodeo rates used.

Figure 7. Rodeo treatment (oz per gallon)

In a previous study of interval treatments of torpedograss with Rodeo, Smith, Langeland, and Hanlon reported that, "Regardless of glyphosate rate or time of re-treatment, torpedograss foliage was completely necrotic within two weeks of every application." And each rate required application of at least four treatments over a 2-year study period for acceptable control. They also reported that "as torpedograss control improved plant diversity increased." (Smith, Langeland, and Hanlon, 1998).

FUTURE RESEARCH

A regrowth study was initiated in August of 1999 in order to confirm whether the roots of the plants were still viable and if in fact they would initiate new growth. Using the same methods and materials, the shoots of the plants will be harvested four weeks after treatment, and the roots will be allowed to regrow for an additional twelve weeks. Torpedograss will be added to the plants already studied, in order to compare regrowth of the target and non-target plants.

ACKNOWLEDGEMENTS

We thank Pete Dingler and Linda Milark for their help with the many hours spent harvesting plants. We also thank Joanne Korvick for her assistance with this project.

REFERENCES

Holm, LeRoy G., et al. The World's Worst Weeds: Distribution and Biology. Honolulu: University Press of Hawaii, 1977.
"List of Florida's Most Invasive Species." Florida Exotic Pest Plant Council. 1997. Online. Internet. Available http://www.fleppc.org/97list.htm.
"National Water Summary on Wetland Resources" United States Geological Survey Water Supply Paper 2425. Online. Internet. Available http://water.usgs.gov/public/nwsum/WSPS2425/statehighlightssummary.html.
Schmitz, Don C., et al. The Ecological Impact of Nonindigenous Plants. Washington: Island Press, 1997.
Smith, Brian and Ken Langeland. "Comparison of Various Glyphosate Application Schedules to Control Torpedograss." Aquatics 20.2 (1998): 4-9.
Sutton, David L. "Growth of Torpedograss from Rhizomes Planted under Flooded Conditions." Journal of Aquatic Plant Management 34 (1996):50-53.

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