Aquatic spraying to control hyacinth and water lettuce on lake

OKEECHOBEE — Florida Fish and Wildlife Commission shared a plan this week to use chemical spraying to control the growth of hyacinth and water lettuce in the Eagle Bay and Kings Bar areas of Lake Okeechobee.

Hyacinth and water lettuce are considered harmful invasive plants.

According to the FWC report, the use of herbicides to control the invasive plants is “necessary to limit ecological damage to the diverse plant communities.”

This graphic from a power point presentation shows areas of harmful invasive vegetation targeted for herbicide spraying on Lake Okeechobee. Special to the Lake Okeechobee News/FWC.

“A survey conducted on April 22 by FWC and U.S. Army Corps of Engineers biologists found 300-350 acres of Water Lettuce and 200 acres of Water Hyacinth,” stated Brendon Heission of FWC in an email shared Wednesday. “The Water Hyacinth in certain areas have grown to upwards of 45 inches tall. Large mats are forming around the lake. These tall Hyacinths are beginning to push over stands of native bulrush. The lake is currently seeing low water levels and this is resulting in the growth of submerged aquatic vegetation. This submerged vegetation is being shaded out in areas where the invasive floating plants are collecting. This treatment is necessary to limit ecological damage to the diverse native plant communities.”

According to the FWC report, on April 22, when the lake level was at 11.5 feet (above sea level), a survey of aquatic vegetation was conducted of Eagle Bay Island and around Kings Bar to Tin House Cove.

Hyacinths push down native bulrushes in this photo shared by the Florida Wildlife Commission. FWC plans to use herbicide spraying to control hyacinths and water lettuce in the Eagle Bay and Kings Bar areas of Lake Okeechobee. Special to the Lake Okeechobee News/FWC.

“A major concern is that large hyacinth is pushing down and killing native bulrush throughout the survey area,” the FWC report states. “Large stretches of lettuce are also mixed with bulrush and covering native lilies and spatterdock. With the rainy season approaching, water levels will rise and the potential for these invasive plants to impact navigation and flood control structures will increase. Native bulrush will likely be removed from sediment as hyacinth is driven to other areas which could negatively impact the ecosystem. Water levels where plants are found remain less that 2 feet in depth so mechanical harvesting is unlikely for this area.

“As most of the invasive plants are within bulrush, Penoxsulam is a likely herbicide to use. However, studies show this takes at least six weeks to start showing signs of effectiveness. That being said, spraying should be of high consideration in this area so plants do not start to impede navigation during the wet season,” the FWC report states.

According to the DOW Chemical product safety assessment website, Penoxsulam is used to control broadleaf weeds in rice fields, golf courses, sports fields and lawn care as well as to control aquatic weeds. It does not harm most grasses. The product safety sheet also notes the product is used in “lakes and ponds – aquatic weeds, notably for the control of hydrilla in Florida at very low use rates.

“The potential for penoxsulam to accumulate in the food chain (bioconcentrate) is low. Penoxsulam is adsorbed by soil and has low-to-moderate leaching potential in most soil types. In soil, penoxsulam is broken down by microbial degradation,” the DOW website states.

“Penoxsulam is highly toxic to aquatic organisms on an acute (single, high dose) basis. It is practically nontoxic to birds on an acute basis and slightly toxic to birds on a dietary basis,” states the DOW product safety sheets.

Earlier this year, hundreds of Florida anglers protested the use of herbicides sprayed into Lake Okeechobee and other state waters in a series of public meetings. Concerns included allegations of over spraying of chemical herbicides, which kill native plants along with the invasives; lack of oversight of those spraying; build up of muck in the lake as the dead invasive plants fall to the bottom of the lake and decay; and health hazards posed to humans exposed to the chemicals.

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