Vol. 15—1961 - NorthEastern Weed Science Society

566.
PROGRESS-R!PORT·ON CONTltOLOF EURASIANWATERMILFOILIN CHESAPEAKEBAY
.' ,
John H. Steenis
Patuxent Wildlife Research Center
U. S. Fish and Wildlife Service
Laurel, Maryland
and
Vernon D. Stotts
Maryland Game and Inland Fish Commission
. Pittman-Robertson Project W-3Q-R
Annapolis, Maryland
INTRODUCTION
.. . Eurasian watermilfoil Q!.yriophyllum spicatum) is widely
. distributed in Europe and Asia and now is spreading rapidly in this
country.' Present in New Jersey since the turn of the century, and in
the Potomac River ~yland and Virginia) since 1933, it has been
repOrted recently in the upper part of Chesapeake Bay and in North
Carolina, New York,' and Tennessee.
Eurasian watermilfoil is closely related to the native
watermilfoil, Myriophyllum exalbescens, found mainly in glaciated areas.
It is very versatile, growing in both fresh and brackish waters. Beaven
(1960) reported that it thrives in waters which are fresh or have a
salinity up to 10 parts per thousand but grows much more slowly at a
salinity of 15 parts per thousand. Since it is absent in more acid
waters, it appears that the alkalinity of brackish water favors growth
in tidal areas. This plant readily withstands 3-foot tides and is found
in water up to 9 feet deep.
The manner in which Eurasian watermilfoil completely dominates
most areas in which it grows has resulted in a severe weed problem. In
many embayments of the Potomac River and elsewhere on Chesapeake Bay, it
often completely replaces native submergent vegetation including valuable
duckfood plants such as widgeongrass (Ruppia maritima), sago pondweed
Potamo eton pectinatus), redhead grass or claspingleaf pondweed
PoUmo eton perfoliatus), and wildcelery (ValUsneria americana). The
native vegetation, however, can withstand more wind and wave action.
A dense but loosely woven blanket of watermilfoil often extends from the
bottom to the surface, restricting water movement. This impedes the
flow of food to oysters and reduces the oxygen supply under the blanket,
which may cause oyster mortality at times. Harvest of oysters, clams,
crabs and fish is hampered severely by extensive growths of Eurasian
watermilfoil. In addition, dense stands curtail-recreational activities