I just received word from Louise Conrad (Department of Water Resources) that there have been recent sightings of Alligatorweed (Alternanthera philoxeroides) in both Suisun Marsh and the Tower Bridge marina in the east Delta. This is a new, noxious, weed to the Sacramento-San Joaquin River Delta system and we should all be on the look out (see photo above and below).
This invasive weed, native to South America, forms floating mats but it is rooted in sediment and has submerged, floating, and emergent forms. This invasive weed can survive a wide range of environmental conditions making it particularly threatening to both aquatic and terrestrial ecosystems. For more information on this weed- please see: http://www.sms.si.edu/irlspec/alternanthera_philoxeroides.htm
In California, currently this weed has been documented near Grizzly Island in August, 2017 and from two other sites further up the Montezuma Slough channel in September.
The introduction point is unknown, but it is clear that this weed is in the Sacramento River and has now moved into Suisun Marsh. Other naturalized locations can be expected. A rapid response to the alligator weed in Suisun is warranted before this invasion compromises planned tidal wetland restoration projects.
On a related note, the invasive yellow flag iris (Iris pseudacorus), and Ludwigia hexapetala (Uruguayan primrose-wllow) are also spreading in these same areas and should be reported as well if found (see details for contact info below).
KEY ACTION POINTS: If you find new populations of alligatorweed (or the other weeds mentioned above) please take photos, GPS points (can be via your smart phone), and a voucher specimen (if possible) to send/email to the State Taxonomist, Genevieve Walden, at CDFA Genevieve.Walden@cdfa.ca.gov
It is crucial to notify Genevieve Walden as we need to document the extent of the problem. If we are not able to control the spread of this weed immediately it will result in similar issues and problems resulting from Brazilian Waterweed, Water Hyacinth and Water Primrose.
What happens if this weed spreads you ask?
Biological control is a possibility, and in fact, one of the biological control agents, the alligatorweed flea beetle, Agasicles hygrophila, has the distinction of being the first biocontrol insect released in the U.S. in order to combat an invasive aquatic weed!
Overall, management impacts on alligator weed by the alligatorweed flea beetle have resulted in a dramatic decrease in the amount of infested aquatic habitat since the insect was first released.
However, the most effective and easiest solution to combating alligatorweed in the California Delta and Suisun Marsh regions is to prevent it from spreading in the first place!
Dr. Julie V. Hopper 