The Saratoga Lake Watershed
Advisory Committee

Managing Non-native, Nuisance Aquatic Plants and Animals

February 1, 2001

Attendees: Joe Finn, Bob Hall, Bob MacMillan, Bradley Birge, Lynnwood Taylor, Peter Balet, Bill Lupo, Alec Mackey, Skip Scirocco, Barbara Farone, Leif, George Hodgson, Jennifer Brady-Connor, Tracey Clothier, Dean Long.

The results from the first year studies on managing Eurasian Water Milfoil were produced and discussed.

Steven LeMere presented his study of the water quality and of the Milfoil weevil impacts. He reviewed the schematic of the weevil life cycle, the site map with research sites indicated, and the table of data. 

Water Quality Monitoring Project (please refer to written overview for additional details)

Surface and deep water samples were collected from four three locations in the Lake and one from Fish Creek.  Study scope was limited by time and funding but enough data was obtained for valuable comparisons to historical data.  

It was noted that of particular importance were the combined results of the Secchi disk, total phosphorous, and Chlorophyll A data that provides an analysis of overall lake water quality, which is very good.  A comparison of all the collected data with historical data shows a trend toward improved water quality, much of which can be attributed to the presence of zebra mussels.

It was also noted that during August the lake was thermally stratified (layer of warm water over much colder water layer).  This resulted in anaerobic (no oxygen) conditions in the cold layer.

The equipment used to obtain the data was demonstrated, including the Sechhi disk , the dissolved oxygen meter, and the [thing that takes water sample from specific depths – the van-something]. 

Herbivore (Experimental Release) Project (please refer to written overview for additional details)

The site used for the herbivore project was located about 150’ offshore the north side of Snake Hill.  Approximately 25, 000 milfoil weevil adults, raised at Cornell University, were released in two separate trips, kept on ice during transport, and sprinkled onto the tips of the milfoil as way of introduction.  Control plots were located on the opposite side of the lake.

Milfoil weevils are naturally occurring in the lake but their numbers are in very low density.  Milfoil grows within a very narrow zone of depth that is prevalent within the lake.  Zebra mussels were found in a range of 125-130 per stem but do not seem to impact the milfoil.  However the zebra mussels needed to be removed for biomass determination, a tedious chore. 

Adult weevils were purchased, at a cost of $1 each, because viability is easily determined and larvae are more easily harmed. The adult weevil can, under certain conditions, produce more than four generations per year under very favorable conditions.  In this instance they were expected to produce 2 or 3 generations maximum.  They have about 15-25 days of egg-laying, 2 per day on average.  Adult weevils raft into shore on pieces of debris to overwinter on sand beaches.  In the spring they swim out to the milfoil beds, and have never been observed to fly. 

The critical milfoil control stage is when the larvae burrow into the apical meristems stems of the milfoil plant.  If air in the stem is lost, the stem will drop out of the upper region of the water column, possibly cutting off its access to light needed for photosynthesis.  Milfoil damaged 3’ down may still photosynthesize if the water is clear enough.  Also, the weevils may introduce vectors of disease, indirectly leading to milfoil weakening or death. 

The results from the first year were mixed due to many factors.  The weevils tended to migrate away from the study plots toward shallow water and toward denser stands of milfoil.  Experimental plots 1, 2, and 3 were disturbed by anglers, resulting in the loss of both milfoil and weevils.  Plots 7 and 8 likely removed a significant amount of weevils as they were migrating out of the control area.  Plots 5 and 6 showed the most exciting results near the end of July, with roughly 95% of the apical meristems damaged.  These two plots also had significantly more weevils per stem at the end of the monitoring period than the other plots. 

2001 studies will involve looking at how many offspring of the stocked weevils overwinter successfully and reappear in the study plots.  It was recommended that the Stafford Bridge sampling site be moved to nearer the Route 9P bridge to eliminate possible addition of Fish Creek to Lake watershed.  It was also suggested that a future milfoil weevil study plot be in a milfoil bed within Fish Creek as no harvesting occurs there.

SONAR Treatment Project

For the first time in Lake history SONAR, purchased by the Saratoga Lake Association, was applied in two 100-acre experimental blocks to try to reduce or eradicate milfoil beds.  Due to water flow through from heavy rains in May and June, the effectiveness of the May and June applications of SONAR slow-release pellets (SRP) was diminished.  The manufacturing company honored its guarantee by providing re-applications of SONAR AS, a liquid form.  The liquid SONAR treatment proved to be effective after six weeks.

SONAR has advantages in that the wide-spread kill-off is so slow it doesn’t cause a decrease in dissolved oxygen due to decomposition. 

This coming year the impact of the applications on milfoil beds and native plants will be reviewed.  By the end of August there will be a better idea on how to proceed. 

Improving Eurasion Water Milfoil Control

Harvesting: Harvesting, a key activity since the mid-1980s, was developed to provide access from docks to navigable waters off-shore.  Over the years it has become more of a mowing program, running about 16 weeks a year and removing 913 loads, or 1000 tons, of wet milfoil.  Harvesting can be done to control milfoil growth by running later into the fall (colder season) and by using bigger harvesters to go deeper.  Both of these actions will change to focus from access and aesthetics to reducing the size of the milfoil beds by increasing stress on the plants.

Annual Drawdown:  Also a key activity since the mid-1980s, the annual drawdown reduces the water level in the lake to expose, dry out, and freeze shallow water zone that, combined with ice scour, also eliminates milfoil. 

SONAR:  It is possible to delay liquid application understanding that the milfoil will remain in the water column during July and mid-August.  The milfoil in the water column may be acceptable to most property owners if they were aware that it was a part of the longer-term solution. It was recommended that the SONAR be applied in the early part of the day when there is less activity on the lake.

If using SONAR lakewide, then mowing will have a negative effect on SONAR’s effectiveness because it disrupts the milfoil beds.  If harvesting, then partial use of SONAR is the most effective way to manage milfoil beds. If paths were mowed and SONAR applied later, a greater biomass of milfoil would be impacted causing more stress and death to milfoil.

It was noted that if SONAR applications continue, there is an inherent conflict of interest in having the same company apply and assess the results.  Also, it was pointed out that a long-term funding source would be needed to increase lake management, and that this source could come from boat or other fees.