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High-Tech Surveillance Nabs Water Weeds

By Ben Hardin
May 24, 1999

The thickest patches of exotic weeds clogging the lower Rio Grande River can’t hide any longer and could get their comeuppance, thanks to high-tech aerial mapping technology developed by Agricultural Research Service scientists.

Beginning last year, the technology helped the Texas Natural Resource Conservation Commission (TNRCC) and the Texas Parks and Wildlife Department detect tons of hydrilla and water hyacinth growing on the river so they could be removed. During last year’s drought, these weeds were sucking up scarce water and obstructing the flow of irrigation water.

Hydrilla, native to Asia, and water hyacinth, native to South America, share a notoriety for clogging marinas, snarling fishing lines and interfering with flood control and hydroelectric power generation. The weeds grow so competitively with other aquatic plants that biological diversity may be threatened in many lakes and streams through southern parts of North America.

ARS and TNRCC researchers used aircraft to acquire color-infrared video imagery that pinpointed locations where the alien vegetation had infested the Rio Grande. The imagery makes water hyacinth appear orange-red and hydrilla appear reddish-brown. The scientists measured the area of infestations by computer analysis of the imagery.

Verification of the data by boat helped advance other research that’s aimed at conducting wider-scale surveys of weed infestations using additional remote sensing, global positioning system and geographic information system technologies. These technologies may help scientists make timely assessments of experimental weed control measures.

ARS is the chief scientific arm of the U.S. Department of Agriculture.

Scientific contact: James H. Everitt, ARS Subtropical Agricultural Research Center, Weslaco, Texas; phone (956) 969-4824, fax (956) 969-4893,

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