2020 ESA Annual Meeting (August 3 - 6)

PS 16 Abstract - Quantitative analysis of the effectiveness of herbicide application on invasive elephant ear (Colocasia esculenta) plants

Tanya Jagdish, Biology, Albion College, Albion, MI and Thomas L Arsuffi, Llano River Field Station, Texas Tech University, Junction, TX
Background/Question/Methods

Elephant ear (Colocasia esculenta) is an invasive plant found along the banks of Llano River, Texas. These plants form extensive monotypic stands that alter the structure and dynamics of native riparian plant communities and evapotranspirates large quantities of water. A multi-year watershed-based management program, started by Texas Parks and Wildlife Department in partnership with TTU Llano River Field Station, aimed at controlling the spread of elephant ears using precise spot herbicide treatments. The river was divided into 15 reaches, ranging 2 to 8 km in length, and were surveyed three times a year, covering 5 reaches per survey on average. Elephant ear stands were documented using GPS enabled cameras and were treated with herbicide. To quantify the effectiveness of herbicide application, the changes in the number and the size of elephant ear stands were examined for each reach for the years 2013 to 2018. The GPS points, indicating the number of stands per reach, were grouped into different rounds of treatment based on each reach’s treatment history. The images were assigned stand size scores based on relative coverage of elephant ear plants per stand. These data were analyzed to see the effectiveness of the management program through treatment years.

Results/Conclusions

The results indicate that herbicide application reduced the number of elephant ear stands to less than 20% of starting number in seven out of the ten reaches with documented elephant ears. In five out of these seven reaches, the number of stands in the first survey of every round of treatment increased from the previous round. This increase is likely to occur when plants are not treated for a long period of time, indicating that continuous treatment of the reaches is necessary to keep the number of stands in control. Image analysis of stand photographs indicate a decrease in large stand size with every successive treatment. Within four treatments, the percentage of large stands decreased to less than 10% of total for stands surveyed, and by the fifth treatment, this number reduced to 0%. This indicates a minimum of four to five treatments is required to see a significant decrease in the number of large elephant ear stands. Although we didn’t measure evapotranspiration, control of elephant ears is viewed as a water conservation measure in the Upper Llano Watershed Protection Plan and may aid in river flows during droughts.