Effectiveness of Herbicide Treatments During Drawdown of East Lake Tohopekaliga

Historically, many of Florida’s freshwater ecosystems experienced natural and sometimes drastic water level fluctuations over time. This process flushed out decaying plant material during the wet season and dried up shorelines during the dry season. This cycle prevented overgrowth of plant communities and accumulation of organic material (muck). In response to human population increases and demands overtime, waterways were manipulated and water levels have been stabilized for flood control with structures such as canals and dams. Unfortunately, water stabilization has promoted excessive vegetation growth in shallow areas in some of Florida’s public lakes. Dense vegetation and associated accumulation of muck has degraded fish and wildlife habitat in many systems, including the Kissimmee Chain of Lakes. FWC has developed management strategies to combat this succession, including lake drawdowns combined with muck removal and subsequent herbicide treatments. These strategies suppress the rapid establishment of noxious vegetation which often follows expensive habitat enhancement projects.

In preparation for a planned drawdown on East Lake Tohopekaliga, FWC researchers from the Freshwater Plants Project partnered with personnel at the University of Florida to evaluate pre-emergent activity of select herbicides in 2018. Results revealed two herbicides that were recommended for use and evaluation on the East Lake Tohopekaliga drawdown: Flumioxazin and Imazamox.

In October 2019, FWC and the South Florida Water Management District began lowering the water levels of East Lake Tohopekaliga, the first drawdown on the Kissimmee Chain since 2004. Following scraping and muck removal efforts, the two previously evaluated herbicides were applied to shallow areas where nuisance vegetation is expected to grow back. This will not only be beneficial to East Lake Tohopekaliga, but it will also provide our team the opportunity to study these treatment areas and evaluate the effectiveness and selectivity of these herbicides. Results from this research will be used to develop improved management strategies for future projects of this type.

Herbicide application on East Lake Tohopekaliga during the 2020 drawdown (left); Study area 1 week after treatment (middle); Study area 3 months after treatment (right).