Hydrilla at the lake


Princeton Hydro will be conducting a treatment event for hydrilla (Hydrilla verticillata) at Harveys Lake on July 30st and August 1st, 2019. The aquatic herbicide that will be used for the hydrilla control is SePro’s SonarOne®, which is used for vegetation management in freshwater systems. SonarOne’s formulation contains 5% fluridone that may cause chlorosis in turf, trees, shrubs, nursery and greenhouse plants if the lake water is used for landscape watering. The desired fluridone concentration for the 30-day interval for optimal hydrilla control is 3 parts per billion (ppb). If irrigation during the 30-day interval is needed for crops and woody ornamental plants, the fluridone concentration should not exceed 5 ppb. For hydroponic farming, greenhouse plants, and nursery plants, the concentration should not exceed 1 ppb. Concentrations can be determined using FasTEST analysis. The landscape watering limitations associated with using SonarOne for hydrilla control is avoiding the use of Harveys lakewater for irrigation for 30 days. 

Hydrilla (Hydrilla verticillata)

📷What is it? Hydrilla is an invasive and exotic submerged aquatic plant species that grows aggressively and is notorious for choking out native aquatic vegetation for resources such as light and space. This species was introduced into North America as an aquarium plant, but was identified as invasive after the plant began to infest waterbodies and pose serious issues to the impacted ecosystems. Hydrilla can be identified by its whorled leaves in bunches of three to eight (most often five) as well as its serrated-edged leaves which feel rough to the touch.  They also have tubers which allow the plant to establish itself in the sediment. The occupancy of hydrilla most often results in the decline of water quality, ecological and recreation value of lakes. Hydrilla was initially a problem in the southeast United States, but now is a growing issue as the species spreads to the north. During an aquatic plant survey in July 2014, hydrilla was identified in the northern end of Harveys Lake in Pennsylvania. The largest stand was located next to the PA Fish and Boat Public Launch. How could it have gotten here? Hydrilla reproduce vegetatively, so living stem sections may break off and then drift and root in different parts of the lake. Carefully checking boats and boat equipment for hydrilla fragments can prevent this “hitchhiker” from infesting. Limiting disturbance to lake bottoms can also minimize the chances of hydrilla fragmentation. Mechanical harvesting, hand pulling, stocking sterile grass carp and using contact herbicides may also help control this invasive species, but these all have unfavorable and short-term effects that may actually increase the spread of hydrilla.

📷Now what? A method that exhibits long-term potential of controlling and ultimately eradicating the invasive and nuisance hydrilla growth as well as having little to no impact on native vegetation presence is through the use of a fluridone-based systemic herbicide (SonarOne®) applied by a state-certified applicator. The goal of this treatment is to protect the aquatic habitat and ecological and recreational value of Harveys Lake. This treatment will also prevent hydrilla from traveling downstream into and infesting the Susquehanna River and ultimately the Chesapeake Bay.

The plan: The proposed grant application covers a treatment of the entire near-shore area (210 acres) of the lake. A pre-treatment survey of the lake and its resident aquatic plant community was conducted in the spring (late April/early May), which provided information on the distribution and abundance of hydrilla during the early part of the growing season. Depending on the water temperatures in July, the entire near-shore treatment of Harveys Lake was conducted by Princeton Hydro’s state-registered applicators using SonarOne® over the course of three to four days. The 4,320 lbs. of SonarOne® was applied to maintain the desired fluridone concentration of 3 ppb (parts per billion) for at least 30 days. This concentration is high enough to kill invasive and exotic species like hydrilla and Eurasian watermilfoil, but low enough that native species like pondweeds will continue to thrive. Three post-treatment sampling events will be conducted in which 20 water samples during each event will be collected for FasTEST analysis (total of 60 samples). The results will determine which specific nearshore locations may need a small increase in fluridone concentration. If all split treatments are completed by late June to early July, a set of post-treatment aquatic plant surveys will be conducted in July or early August, while the second will be conducted in September or early October.

Potential issues: Regarding landscaping purposes for the duration of the 30-day treatment interval, it is not recommended that the lake water undergoing treatment be used for watering. SePro’s SonarOne® Aquatic Herbicide fact sheet states that trees and shrubs using the water treated with this product may occasionally develop chlorosis (leaves producing insufficient chlorophyll). It also states that for irrigation of hydroponic farming, greenhouse and nursery plants that the concentration of SonarOne® must be below 1 ppb, and for the irrigation of woody ornamental plants that the concentration must be below 5 ppb. For irrigating crops such as tomatoes and peppers, the concentration must not exceed 5 ppb. Since 3 ppb is the maximum and desired concentration for hydrilla eradication, using the treated water may be an exception in some cases.

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