Mechanical control of eurasian watermilfoil in Maryland with and without 2,4-D application

Abstract

Eurasian watermilfoil (Myriophyllum spicatum L.) increased from a minor annoyance of a few thousand acres in the late 1950’s, to a major nuisance covering over 200,000 acres in waters of the upper portion of the Chesapeake Bay in 1964. From 1961 through 1964, the effectiveness of underwater mowing of milfoil using a mechanical mower with and without subsequent application of 2,4-dichlorophenoxyacetic acid was investigated in medium and near maximum salinity ranges for milfoil in tributaries of Maryland’s western shore. Milfoil normally reaches the surface by early May, and begins to sink in high salinity waters about September 15, and in lower salinities about October 15. Depending on the type of activity for which milfoil control is instituted, mowing must be repeated at least monthly during the usual mid-May to mid-September growing season. In this study it was effective only for the season in which it was made. New nodal growth to 18 inches or more per month from cut milfoil stems or fragments made cutting impractical for large areas. Cutting followed by herbicide application when new growth offered sufficient vegetative containment of applied 2,4-D impregnated attaclay granules extended milfoil’s vulnerable period to 2,4-D beyond anthesis. The butoxyethanol ester of 2,4-D was more effective than the iso-octyl ester. In study plots no adverse affects were noted to endemic fauna. Prime submersed waterfowl food plants, previously retarded by the dense milfoil over-story, made rapid growth once the milfoil was thinned or removed. These preferred waterfowl foods evidenced no undesirable responses to either cutting or to 2,4-D.