Effect of Citric Acid, Copper Sulfate Concentration, and Temperature on a Pond Shoreline Treatment for Control of the Marsh Rams-Horn Snail Planorbella trivolvis and the Potential Toxicity of the Treatment to Channel Catfish

Abstract

Tests were run to determine whether any refinements were warranted in an established copper sulfate–citric acid pond shoreline treatment (Environmental Protection Agency registration number 1278–8) for aquatic marsh rams-horn snails Planorbella trivolvis. The treatments applied in these studies consisted of two levels (full and half) of copper sulfate (CuSO₄; 589 and 294.5 g) with and without citric acid (CA; 58.9 and 0 g) that were delivered in a 2-m swath 10-m length of shoreline. In research ponds, shoreline treatments without CA were significantly more effective against the snails than the treatments with CA. The full CuSO₄ treatment without CA was significantly more effective than the half treatment without CA at all temperatures tested below 35°C. There was a significant reduction in the effectiveness of the full treatment without CA at 17 ± 0.5°C (40% snail survival), while snail survival (average, 3.2%) in the trials run at 21.5, 23, 26, and 35°C was not significantly different from each other. When applied to the perimeter of 0.41-ha research ponds (ponds smaller than recommended for the shoreline treatment), the full CuSO₄ treatment with CA was found to be significantly more toxic to channel catfish Ictalurus punctatus over a 120-h period at 31°C (<35% survival) than at 28°C (>95% survival, which was similar to that of the control). It was also more toxic than an application of the same amount of CuSO₄ without CA at 31°C. The study indicates that the most effective pond shoreline treatment (589 g of CuSO₄ without CA applied in a 2-m swath over a 10-m length of shoreline) should be administered in water with a temperature of at least 21°C.