Effects of 2,4‐dichlorophenoxyacetic acid on fungal propagules in freshwater ponds

The effect of treatments with 2,4-dichlorophenoxyacetic acid (2,4-D) on fungal propagules in man-made freshwater ponds was studied as part of a larger investigation into the effects of the herbicide on the ponds' ecology and chemistry. Myriophyllum spicatum was planted in the ponds as a target plant; the ponds were allowed to stabilize before being treated with dimethylamine (DMA) and butoxyethylester derivatives of 2,4-D (1 mg/L). Although the 2,4-D treatments were highly toxic to M. spicatum in the ponds (B. F. Scott et al., 1985a) they did not have a clear effect on fungal propagule levels in either the water column or sediment, which indicates the absence of a primary effect. The mean levels of molds and “total fungi” in both pairs of treated ponds, and of yeasts in the DMA-treated ponds, tended to be depressed relative to the control ponds, for up to 114 days after treatment. That observation was reinforced by plots of the accumulated differences between the treated and control ponds. The differences between the mean fungal levels in the control and treated ponds were erratic, however, and the study's design did not permit a thorough statistical analysis of the data, although a multiple comparison test detected some differences (p < 0.05) between propagule levels, particularly molds, in the treated and control ponds. If real, the trends were probably a result of unidentified secondary effects of the pond treatments. The results imply that applications of 2,4-D to aquatic vegetation at realistic rates do not drastically affect fungal propagule levels in the water column or sediment. © 1994 by John Wiley & Sons, Inc..