Integrated Pest Management Controls Water Hyacinth

Water hyacinth control had evaded land managers for many years and choked the life out of lakes and ponds. In the late 1990s, researchers from Florida discovered that the aquatic weed could be most effectively controlled through integrated pest management.

Water hyacinth (Eichhornia crassipes) is a noxious, mat-like water weed that clogs waterways, snuffs out light for freshwater species living below the surface and snags boats unlucky enough to cross its path. Since the 1990s, Dr. Ted Center from USDA-Agricultural Research Service in Florida has been refining integrated pest management approaches to best keep water hyacinth under control. He has discovered that the weed is most consistently managed when it’s healthy.

Why? Healthy plants build populations of healthy predatory weevils.

Until the 1970s, herbicides were the only method of control for water hyacinth. In 1972, a biocontrol weevil (Neochetina eichhorniae) was released, followed by another (N. bruchi) in 1974. However, many land managers continued to use herbicides to completely kill water hyacinth populations, even where biological control seemed to keep the plants in check. Once the water hyacinth was gone, the weevils also began to die off.

In a 1999 peer-reviewed article in Environmental Management, Dr. Center and colleagues from the University of Florida, the Florida Department of Environmental Protection and the US Army Engineer Waterways Experiment Station tested whether herbicides—used to reduce water hyacinth populations rather than extinguish them—could help manage the water hyacinth while maintaining the weevils.

Their research showed that weevil populations actually thrived when plants received moderate herbicidal treatments.

A follow-up research project in 2010 further supported his 1999 findings. In fact, he discovered that the weevils’ ability as effective biocontrol agents depended on their ability to reproduce. The more nutritious the water hyacinth, the more the weevils could reproduce. N. bruchi was more sensitive to plant quality than N. eichhorniae. In fact. Center says that if plants were scarce in nutrients, N. bruchi may disappear altogether from that site.

Areas that were already managed with herbicidal control tended to have plants that were more highly nutritious. For maximum control of water hyacinth, land managers should integrate both biocontrol agents and herbicides.

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