In cooperation with University of California scientist and others, ARS plant
pathologist Lars Anderson researches treatments that will stem the growth of
aquatic weeds such as Eurasian watermilfoil.
In aquatic weed known as Eurasian watermilfoiland its rascally cousin
parrotfeathercan quickly take over lakes, rivers, irrigation canals, farm
ponds, and other watery habitats. They crowd out desirable native vegetation,
clog irrigation systems, and make waterways unsuitable or unpleasant for
boating, fishing, and swimming.
Native to Europe and Asia, Eurasian watermilfoil, Myriophyllum
spicatum, has been found throughout the United States. Parrotfeather,
Myriophyllum aquaticum, an escaped South American species, is less
pervasive in the United States than Eurasian watermilfoil. However,
parrotfeather forms denser stands that make ideal breeding grounds for
At Davis, California, ARS plant
physiologist Lars W.J. Anderson and colleagues in the agency's Exotic and
Invasive Weed Research Unit are seeking new ways to control the two weeds.
Working with scientists at the University of California, Davis, they've shown
for the first time that a widely used aquatic herbicideapplied to
above-water shoots of parrotfeathermay appear effective at first, but
does little to knock out the extensive underwater growth of the weed.
A better tactic for the future may be to apply the herbicide triclopyr below
the water surface. The ARS scientists were the first to test this chemical on
parrotfeather. They conducted the experiment at a 20-acre lake in the oak
woodlands of Beale Air Force Base in northern California. The lake has been
infested with this weed for about 20 years.
Plant physiologist Lars Anderson checks watermilfoil for shoot production.
Anderson did the work under terms of an experimental use permit from the
U.S. Environmental Protection Agency. He collaborated with resource managers at
the base and with Dow AgroSciences LLC, which markets the herbicide as Garlon
3A for use in other ecosystems. So far, according to Anderson, triclopyr worked
better than any other option tested at the lake.
Anderson and co-researchers are also conducting sophisticated laboratory
analyses of the two milfoils to precisely identify differences in the genetic
makeup of these weeds from different sites. That approach could boost the
success of biological control insects such as the watermilfoil weevil,
For best results, weevils recruited to stop the spread of the weeds should
be matched as closely as possible to Eurasian watermilfoil plants most
genetically similar to those from which the insect was collected. University
scientists in Vermont and Minnesota have already conducted some biological
control tests with this little brownish-black insect.
Other ARS investigations have revealed differences in the chemical makeup of
Eurasian watermilfoil. Those differences might affect the plant's nutritional
value to the weeviland thus the weevil's vigor, according to ARS
ecologist David F. Spencer at Davis. Nitrogen in Eurasian watermilfoil plants
sampled from the Truckee River in California, for instance, was "lower
than the nitrogen content in plants sampled from a shallow research pond at the
Davis lab," says Spencer.
Eurasian watermilfoil, Myriophyllum spicatum, at flowerin
"Studies done by ARS scientists in Florida," he notes,
"showed that the relative growth rate of a weevil that eats a water weed
called hydrilla increased by 50 percent when the weevil was fed plant material
with 3.5 percent nitrogen, as compared to plant material with only 2 percent
Based on those results, differences in nitrogen in Eurasian watermilfoil
plants from various sites might also make a difference in how fast the helpful
weevils developand how effectively they foil these notorious
weeds.By Marcia Wood,
Agricultural Research Service Information Staff.
This research is part of Crop and Commodity Pest Biology, Control, and
Quarantine, an ARS National Program described on the World Wide Web at
Lars W.J. Anderson and
David F. Spencer are in the USDA-ARS
Exotic and Invasive Weed
Research Unit, c/o UC Davis, One Shields Ave., Davis, CA 95616; phone (530)
752-6260 [Anderson], (530) 752-1096 [Spencer)], fax (530) 752-4604.
"Foiling Watermilfoil" was published in the
March 1999 issue of Agricultural