COMPARING SPRING TREATMENTS OF 2,4-D WITH BOTTOM FABRICS TO CONTROL ANEW INFESTATION OF EURASIAN WATERMILFOIL

Control of Eurasian watermilfoil (Myriophyllum spicatum L.) at Beulah Lake, southeastern Wisconsin, was compared using a single treatment of 2,4-D (2,4-dichlorophenoxyacetic acid) in May 1993 at 80% of the maxi mum rate and polyvinyl-chloride bottom fabrics (0.50 mm thick) applied for 45 days from mid-May through early July 1993. A plastic curtain s uspended across the outlet of each treatment cove kept 94 to 98% of th e herbicide from drifting into open water. Both control methods elimin ated Eurasian watermilfoil from treatment sites within 4 to 6 weeks. T he bottom fabrics eliminated all species of rooted, submerged aquatic plants. The 2,4-D treatments initially reduced the mean standing crop of coontail (Ceratophyllum demersum L.), elodea (Elodea canadensis Mic haux), variable-leaf watermilfoil (Myriophyllum heterophyllum Michaux) , and wild celery (Vallisneria americana Michaux) by 14 to 85%. These native plants, however, recovered about 80% to 120% of their standing crops within 10 to 12 weeks after herbicide treatments, while transpla nts of these species showed poor colonization on sites previously cove red with bottom fabrics. Herbicide concentrations in the water column at the treatment sites dropped 37 to 48% within 3 weeks of treatment a nd 70 to 82% within 6 weeks of treatment.