Presentation on the invasive plant Alligatorweed.

1. Ryan M. Wersal, Ph.D.
Mississippi State University
Geosystems Research Institute
Missouri Department of Conservation Invasive Plant Workshop
Powder Valley Nature Center, Kirkwood, MO May 16th and 17th

2. Benefits of Aquatic Plants
 Stabilize lake sediments, reduce
resuspension
 Increase sedimentation, reduce
turbidity
 Provide habitat for insects, forage
fish, fish spawning and YOY fish
 Provide food for waterfowl, other
animals

3. Non-native vs. Native Community
Myriophyllum spicatum Vallisneria americana
Eurasian watermilfoil Water celery

4. Canopy Structure

7. Alligatorweed
(Alternanthera philoxeroides)
 Emergent perennial native to South America (Vogt et al. 1979)
 Nuisance aquatic species in over 32 countries worldwide
(Gunasekera and Bonila 2001)
 Major problem in Southern U.S. aquatic and riparian areas
(Kay and Haller 1982)
 Hollow stems form extensive, dense mats on water surface
(Kay and Haller 1982)
 Impedes boat traffic, increases flood risk, clogs irrigation
canals, harbors pathogen-carrying insects, reduces overall
water quality and property value (Madsen 2004)

8. Alligatorweed distribution in the
United States by Hydrologic Units

9. Alligatorweed distribution in the MidSouth Region

10. Alligatorweed Habitat
 Nuisance in subtropical
aquatic and wetland areas,
can be rooted in submersed
to moist soil, especially ditch
and stream habitats, forms
floating mats
 Major problem in the Ross
Barnett Reservoir and MS
Delta
 Potentially has two biotypes Ross Barnett Reservoir, MS

11. Alligatorweed ID
 Non-native emergent perennial
plant
 Emergent or submersed
 Stems form a tangled mass
 Leaves simple and opposite on
stems
 Leaves elliptical
 Typically glabrous (very little if
any hair)

12. Alligatorweed ID
 Several-flowered whitish
head
 Flowers borne in leaf axils
 Flowers always on stalks up
to 2 inches in length
 Mature seeds not known to
occur
 Spread via vegetative growth
and fragmentation

13. Alligatorweed ID
 Key identifying characteristic:
 Stems almost always hollow

14. Can Be Confused With:
 Sessile joyweed (Alternanthera sessilis)
 Not widespread
 Ludwigia spp.
StarrImages
Kim Starr

15. Ecological Impacts
 Degradation of water quality
 Reduction in species diversity
 Suppresses native plant species
 Potential impacts on endangered
species
 Alters animal communities

16. Lake Jackson, MS Blue Lake, MS
Little Eagle Lake, MS Blue Lake, MS

17. Human Use Impacts
 Reduces access to water
 Reduces property values
 Limits recreation
 Impedes navigation
 Increases flood duration
& intensity
Lake Jackson, MS
 Human health Alligatorweed

18. Management Options
 Biological
 Chemical
 Mechanical
 Physical
 Institutional

19. Alligatorweed Management
Biological
Alligatorweed flea beetle
Stem borer moth
Chemical
2,4-D, triclopyr, imazapyr,
glyphosate
Mechanical - None
Physical - None

20. Biological Control
 Alligatorweed flea beetle
(Agasicles hygrophila)
 Works well south of
Vicksburg-Jackson-
Montgomery (I-20
corridor)

21. Biological Control
 Stem borer moth (Vogtia malloi)
 Active throughout MS
 May be more of an option for
Missouri than flea beetle due to (Photograph courtesy USDA, ARS by Willey C. Durden.)
climate
 Typically not present near
agricultural areas where
insecticides are used
(Photograph courtesy USDA, ARS)

22. Small Scale Trials
 Imazapyr, triclopyr, glyphosate (DIA salt and IPA salt),
imazamox, 2,4-D, diquat (maximum label rate), and
penoxsulam (maximum label rate) offered similar effective
control for 12 weeks
 Carfentrazone and diquat provided rapid biomass
reduction but regrowth began within days after
application

23. Field Control
 Imazapyr, 1 to 4 pints/acre
 Triclopyr, 3 to 8 quarts/acre
 2,4-D, 2 quarts/acre
 Glyphosate, 2 quarts/acre
 Non-ionic surfactant, 1 pint/acre
 In Mississippi, 2,4-D and glyphosate are being used
alone or as a tank mix
Always read the herbicide label

24. Hobbs and Humphries 1995. Conserv. Biol. 9:761-770.

25. Other Resources
UNIVERSITY PROFESSIONAL SOCIETY
Center for Aquatic and Invasive Plants Aquatic Plant Management Society
aquat1.ifas.ufl.edu www.apms.org
Mississippi State University GRI North American Lake Management Society
www.gri.msstate.edu www.nalms.org
MSU Extension Service GOVERNMENT
msucares.com/pubs/publications/p1532aquat Aquatic Plant Control Research Program
ic.pdf www.wes.army.mil/el/aqua/aqua.html
USGS Aquatic Nonindigenous Species Site
FOUNDATION nas.er.usgs.gov
Aquatic Ecosystem Restoration Foundation
www.aquatics.org

26. Ryan Wersal, Ph.D.
Geosystems Research Institute
Box 9652
Mississippi State, MS 39762
Ph (662) 325-4595
Fax (662) 325-7692
rwersal@gri.msstate.edu