The FWC Invasive Plant Management Section has invested significantly in research through the years on biological, mechanical, and physical means to control aquatic plants, used alone or in combination, to augment or replace herbicide use. Additionally, much research has been conducted to understand the physiology and growth patterns of target invasive plants in Florida waters to reduce management needs regardless of the technique.
Pesticide use is reduced in several ways: by using management strategies that integrate pesticides with other control tools when appropriate, and by using strategies that minimize pesticide use when pesticides are applied alone. Following are steps taken by FWC and other aquatic plant managers to reduce pesticide use when controlling aquatic plants in Florida waters. You can read more about specific control methods in Section 3 and you can read more about considerations for each control option in Section 4 of this website.
Nearly 20 insect species and plant pathogens have been released to control six invasive plants in Florida waters with varying degrees of success. Additionally, sterile grass carp have been stocked in more than 90 public lakes and nearly 20,000 private ponds to control submersed aquatic plants, especially hydrilla.
Generally, mechanical and physical controls are labor-intensive and are not used extensively in Florida’s aquatic plant management program. A notable exception is water level manipulation where reservoir levels can be temporarily lowered, decreasing the volume of water and reducing the amount of herbicide needed by as much as 50% to control submersed plants. After plants are controlled, increasing the water levels reduces light penetration, to further stress the targeted submersed plants and delay their recovery.
FWC biologists monitor 1.26 million acres of public lakes and rivers each year to detect new invasive plant introductions in an effort to eradicate these plants before they establish and become widespread, long-term management problems. This strategy is known as Early Detection Rapid Response (EDRR). FWC has aquatic plant control contractors available for immediate deployment and reserves up to $500,000 each year toward eradicating invasive aquatic plants new to the state or, in the case of established species, new to that waterbody.
Savvy managers take advantage of environmental events to help control aquatic plants. For example, tropical storms or hurricanes can increase turbidity and tannin content, or increase water levels by several feet. All of these conditions stress submersed plants such as hydrilla by substantially reducing light penetration. Even low rates of herbicides can then collapse plants, further removing them from surface sunlight required for photosynthesis, and extending the amount and duration of control.
FWC offers certain exemptions from aquatic plant control permitting if stakeholders agree to use physical or mechanical vs. chemical means.
This is the cornerstone of FWC’s invasive plant management strategy – a concept known as Maintenance Control. Eradicating established invasive plants is at best difficult, and in many cases impossible. Using Maintenance Control, invasive plant populations are suppressed to the extent practicable in public lakes and rivers through frequent, but small-scale control efforts, minimizing herbicide use and overall control costs.
FWC contracts with research institutions to determine, through laboratory analysis and operational observation, the lowest amounts of herbicides that will control target plants. This strategy reduces pesticide use and management costs and increases target plant selectivity.
FWC advocates controlling aquatic plants as early as possible in the growing season. Mature plants can accumulate significant carbohydrate reserves in the stems or underground rhizomes and become much more difficult to manage, sometimes requiring multiple herbicide applications to achieve control.
Aquatic plants must be actively growing for maximum herbicide uptake. Once plants mature or begin to senesce, herbicide uptake is reduced. Twice the herbicide may be needed for the same level of control.
Strategies that can reduce herbicide use while improving control include using adjuvants that enhance herbicide uptake or using strategies such as pellet formulations or deepwater trailing hoses that place herbicides at the bottom of the waterbody to control submersed plants.
FWC evaluates and implements the use of combinations of herbicides that control target plants using lower rates than if either herbicide was applied alone. Benefits include improved control of target plants, increased selectivity to conserve non-target plants, overall reduction in pesticide use, and improved herbicide resistance management.