Exotic water primroses (Ludwigia spp.) are aggressive invaders in both aquatic and riparian ecosystems. The plants form dense mats over the water surface. These mats constrain navigation and interfere with recreational activities, irrigation, drainage, and agricultural production. Rapid growth of these weeds also displace native plants and wildlife in aquatic ecosystems.

In the US, several exotic Ludwigia taxa have naturalized and become invasive: Ludwigia hexapetala, L. peploides subsp. peploides, L. peploides subsp. montevidensis, and L. grandiflora. Stakeholders are eager to get these weeds under control by all means necessary and one option is...

Arundo or giant reed (Arundo donax) is invasive in riparian areas in much of central and southern California, as well as other parts of the U.S. In the Sacramento-San Joaquin Delta, arundo grows on islands and along the edges of sloughs and canals. It is also common along the water's edge in the watersheds upstream of the Delta. This giant grass can grow to 20 ft tall or more and from a distance might be mistaken for corn. Arundo stems act like giant straws, wasting Delta water as the stems rapidly grow during the spring and summer. Dense mature patches of arundo block access to water, destabilize flood levees and constitute a fire hazard. For these reasons, the U.S. Army Corps of Engineers and various state and local agencies...

Through a partnership with National Aeronautics and Space Administration (NASA), as a part of the U.S. Department of Agriculture – Agricultural Research Service (USDA-ARS) Delta Regional Areawide Aquatic Weed Project (DRAAWP), NASA has developed Floating Aquatic Vegetation (FAV) mapping tools intended for operational use by DBW.  An initial tool based on the Landsat Satellite provided Division of Boating and Waterways (DBW) with map imagery from satellite data that depicted live water hyacinth and water primrose acreage of areas with 30-meter pixels at approximately 14-day intervals.  The FAV Mapping Tool is being modified to utilize a new satellite, Sentinel-2, with increased spatial and spectral resolution as well as...

The Madsen lab is working on South American spongeplant (Limnobium laevigatum), a relatively new invader in the Sacramento-San Joaquin Delta (Photo 1). Spongeplant is a floating aquatic weed that somewhat resembles waterhyacinth and can be found alongside waterhyacinth in backwaters and along river edges. Photo 2 shows the spongy, air-filled underside of the spongeplant leaves, which allow them to float on the water surface.

Photo 3 is from a trial measuring the spread of South American spongeplant over the water surface at different water temperatures in the laboratory. This will help us to predict the timing of growth in the field, which will inform management decisions.

Photo 4 shows a spray chamber...