Eurasian Water Milfoil Treatment in a Isolated Illinois River Floodplain Wetland Tharran Hobson, The Nature Conservancy and Wayne Herndon, Illinois Department of Natural Resources During fall 2004 staff discovered a small one acre size population of exotic Eurasian water-milfoil (Myriophyllum spicatum) growing in a shallow water section of wetland on the preserve. Given the aggressive nature of this invader, plans were made over the winter to begin treatment before the next growing season. Through consultation with IDNR Fisheries Biologist Wayne Herndon a treatment schedule was developed to begin in May IDNR has made trials and had success with aquatic herbicide applications for the control of milfoil at sites around the state. Dow Chemicals DMA-4 IVM, a liquid formulation of the dimethylamine salt of 2,4-D was chosen due to success Herndon had experienced and safety of the product. Concentrations of between.5 and 1 part per million active product ingredient in the water column was the goal to eradicate milfoil without harming desired native submerged vegetation. Formulas were used to determine the total acre-feet of water present in the 600 acre wetland and further calculations broke total gallons down into pounds of water present. Based on this, it was determined exactly how many gallons of product to use to achieve the desired.5-1 part-per-million active ingredient concentration. By application time in late May it was estimated the small population had grown to cover nearly 100 acres. DMA-4 IVM was applied using a boat bailer to draw the product from a boat mounted container. The entire water body was treated using a grid pattern to evenly distribute the herbicide via the motor prop wash. Follow up monitoring one month post application showed encouraging evidence that the exotic milfoil was in advanced decline while native coontail, elodea, and potamagetons appeared unharmed. Further inspections later in the season revealed no apparent live water milfoil specimens anywhere within the water body. Staff plans to monitor the wetlands at least twice yearly for early detection of re-infestations. It may not be possible to totally eliminate the robust exotic and there is always a chance waterfowl, the suspected initial vector, may introduce new populations in the future. To determine how much product was necessary the following information was needed: Determine the acre-feet of water present. Based on contour maps it was determined the water area was 600 acres. Using the same contours the average depth was estimated at 2 feet. The total acre-feet of water present was 1,200 (600 x 2). Determine the weight of the water present. One acre foot of water contains 326,000 gallons. One gallon of water weighs 8.3 pounds. One acre-foot of water weighs 2,705,800 lbs. (326,000 x 8.3). 1,200 acre-feet of water weighs 3,246,960,000 lbs. (1,200 x 2,705,800) Determine the amount of product to use to reach a 1 part-per-million concentration of active ingredient of herbicide in the water column. DMA-4 IVM has 4 pounds active ingredient per gallon. 80 gallons of DMA-4 is equal to 320 lbs. active ingredient (4 x 80). 320 lbs. active ingredient in the total amount of water present is a concentration of less than 1 part per million (320 / 3,246,960,000 =.98 parts-per- million). Close up of Eurasian water milfoil, an aggressive submerged aquatic exotic. Waterfowl were most likely a vector for the exotic plant. Map above showing spread of the exotic invader over a short period of time. Above and below: Eurasian water milfoil threatened the diversity of restored wetland communities within the Merwin Preserve at Spunky Bottoms. The product we chose to use was Dow’s DMA-4 IVM an approved aquatic version of 2-4D. One month after treatment: On the left is milfoil beginning to die back. On the right is native coontail and elodea clearly unharmed. The method of product dispersal Venturi effect acted to pull product from a boat mounted tank through the motor mounted bailer. Operating the boat along a grid pattern evenly distributed product throughout the water body. USDA