Even the toughest weeds have their mortal enemies. For hydrilla, it's Mycoleptodiscus terrestris. Now, scientists' efforts to turn this fungal foe into a biological control agent could prove even deadlier to the aquatic weed.
Agricultural Research Service (ARS) microbiologist Mark Jackson and U.S. Army Corps of Engineers (USACE) plant pathologist Judy Shearer chose the fungal pathogen for its specificity and cell-wreaking attacks on hydrilla. Mark Heilman of SePRO Corp., Carmel, Ind., is collaborating with them to try and commercialize the fungus as a biological herbicide.
Originally sold in the 1950s for aquarium use, hydrilla has become a noxious weed of lakes, rivers, canals and other water systems across the southern United States and in Atlantic and Pacific coast states. Its dense mats can clog drainage and water-intake systems, impede boating and degrade fish and wildlife habitat.
Herbicide spraying is the chief means of battling hydrilla, though few herbicides are registered for the task. Fluridone is among the most effective, but in parts of Florida and Georgia, prolonged use has brought about resistant strains of hydrilla, increasing treatment costs and impacting performance, notes Shearer, with USACE's Army Engineer Research and Development Center, Vicksburg, Miss.
Since 2000, Shearer and Jackson, with ARS' National Center for Agricultural Utilization Research, Peoria, Ill., have collaborated on developing M. terrestris for integration with chemical and cultural hydrilla-control strategies. In May 2003, their efforts led to a patented new method (6,569,807) of culturing the fungus and "coaxing" it to form tiny, filamentous clumps called microsclerotia. Studies have shown that microsclerotia withstand the rigors of drying and prolonged storage better than the fungus' spores.
Fortunately, they're just as deadly to hydrilla. When dusted onto potted hydrilla in aquarium trials, the microsclerotia reduced plants' above-ground growth by 99 percent. In December 2005, SePRO licensed the scientists' formulation techniques, though testing continues to determine which bioherbicide formulation works best. Once found, it'll undergo larger-scale testing, including small ponds at USACE's Lewisville (Texas) Aquatic Ecosystem Research Facility.
ARS is the U.S. Department of Agriculture's chief scientific research agency.