Applied ecology of Eurasian watermilfoil (Myriophyllum spicatum L.) in Fall River, CA

Eurasian watermilfoil (Myriophyllum spicatum L.) infests the Fall River in Shasta County, CA. In 2003, the aquatic weed infestation resulted in decreased flow rates leading to a broken levee, the flooding of 3000 acres of grazing land, and shutting down the local hydroelectric power generation for six days. Over ;All available controls will likely have some effect on the river. Therefore, it is necessary understand the lifecycle of the weed with regard to patterns in the seasonal allocation of total nonstructural carbohydrates (TNC) and the plant's distribution within the river. This will assist the determination of effective control strategies while minimizing effects to native wildlife, flora, and agriculture.;Total nonstructural carbohydrates are stored in the root crowns over winter and used for regrowth during the next season. Canopy removing controls implemented when TNC are at minimal concentrations in the root crowns could encourage the use of remaining TNC for regrowth. Root crowns were sampled every 2 to 6 weeks for three years (2005 through 2007) and analyzed for TNC concentration. TNC were observed to be lower than an established critical concentration, levels observed in other watersheds, and were lowest during the months of June, July, and August.;Eurasian watermilfoil has appeared to be distributed to downstream regions of the river. If this distribution resulted from lack of introduction upstream rather than natural limitation within the river, the plant can be expected to colonize upstream in the future. Control strategies could be adjusted for the cause of the distribution pattern. Sediments from upstream (uninfested) and downstream (infested) locations were used to grow individuals (with and without nutrients added) to determine if sediments affected growth, tissue nitrogen, tissue phosphorus, and determine how sediments affect distribution. Although tissue phosphorus and nitrogen were affected, growth was not affected indicating that distribution was not affected by sediments or was affected by another untested, limiting factor within the sediment.