They clog canals and pumping stations, they reduce water flow, and they increase water evaporation 4 to 5-fold.
Many irrigation canals and other waterways in the Rio Grande Valley are infested with aquatic weeds—namely hydrilla and water hyacinth. In May, specialists with Texas Cooperative Extension initiated a demonstration in Hidalgo County Irrigation District No.1 that utilizes grass carp for control of hydrilla.
This demonstration, funded in part through the Rio Grande Basin Initiative, extends work already being conducted by Cooperative Extension and others to control aquatic weeds in Brownsville and Rancho Viejo. The office for Hidalgo County Irrigation District No. 1 is in Edinburg, Texas.
“Hydrilla and water hyacinth are nonnative,” said Extension Fisheries Specialist Michael Masser, who is leading the demonstration. “When they were brought to the United States, they were brought without diseases or natural enemies. As a result, they have infested many natural waters in the U.S., including the Rio Grande Valley.”
In irrigation canals and mains, water hyacinth and hydrilla combine to form living dams, requiring that more water be pumped and wasted to break through the weeds. Masser said the introduction of grass carp to control the hydrilla is ideal for irrigation districts, which severely limit the use of pesticides in irrigation water.
Named for their unique ability to consume aquatic plants, grass carp prefer submersed plants like hydrilla. The carp are sterile, eliminating the risk of overpopulation in the canals.
Masser said the Extension team recommended stocking 5,500 grass carp in May–a rate of 40 per vegetated acre.
“This is a high stocking rate,” he said. “We wanted to provide immediate control of the problem in Edinberg, where they had to pump more water than was actually needed in order to break through the weeds.”
The district had already spent more than $100,000 in mechanical control, using a track hoe to mechanically clear the weeds. Masser said grass carp provide a more economical and longer-lasting solution.
Masser and his team recorded 139 surface acres of hydrilla in Hidalgo County Irrigation District No.1 when they initially stocked the carp. They will monitor the vegetation cover and growth of the grass carp over time to evaluate their effectiveness.
