MEMORANDUM

TO: Chute Lake Protection and Rehabilitation District

DATE: November 30, 2010

SUBJECT: Results of the October 19, 2010 survey for exotic species on Chute Pond, Oconto County

Management History

2008

On May 15, 2008, Cason & Associates staff surveyed Chute Pond to map the distribution of exotic aquatic plants. Results of this survey indicated that nearly 53 acres of curly-leaf pondweed and approximately nine acres of Eurasian watermilfoil were growing in the lake. On May 22, 2008 the full distribution of curly-leaf pondweed was treated on Chute Pond with Aquathol K® (liquid endothall). On June 18, all locations of Eurasian watermilfoil were treated with Navigate® (granular 2,4-D). These were the first treatments of their kind on Chute Pond.

2009

On May 15, 2009, 27 acres of curly-leaf pondweed and 10.5 acres of Eurasian watermilfoil were mapped in Chute Pond. Most of these locations were found outside of the previously treated areas in 2008. Cason & Associates, LLC staff treated these areas on June 9, 2009 with Navigate® at a rate of 150 lbs/acre. At the time of treatment, additional locations of milfoil were found. Again these areas were outside previously treated or mapped locations. In total, an additional 20.6 acres of milfoil were identified. On June 25, 2009, these newly discovered areas were treated in the same manner as the previous treatment. Treatments for curly-leaf pondweed were suspended due to the increased urgency in milfoil management as well as budgetary considerations.

During the 2009 season, weed harvesting took place on Chute Pond, but only in a limited fashion. Maps of the known milfoil distribution were provided to the harvester operators with the understanding that they were not to operate within or adjacent to the areas indicated. This was intended to reduce the amount of milfoil fragments and limit the plant from further spreading.

A survey done on October 13, 2009 found that Eurasian watermilfoil had greatly increased in abundance in Chute Pond. Areas that had been treated in the spring of 2009 yielded positive results in reducing milfoil, but the milfoil had spread to other parts of the lake. In total, approximately 109.4 acres of milfoil were mapped (Figure 1).

2010

Over the winter of 2009 and 2010, the District decided on chemical treatment as the most feasible management approach. On May 18, 2010, all 109 acres of Eurasian watermilfoil were targeted using Navigate® at a rate of 100 lbs/acre, along with 27 acres of curly-leaf pondweed using Aquathol K®. Prior to treatment, the water level was lowered and the dam was closed to minimize dilution and increase the chemicals’ contact time with the milfoil. During the summer, all cutting activities were suspended in order to minimize the spread of milfoil.

Methods

A post-treatment survey of Chute Pond was conducted on October 19, 2010 to assess the effectiveness of the treatments. This survey was also used to document additional areas in need of treatment. Utilizing the point-intercept map provided by the Wisconsin DNR, the presence or absence of exotic species (namely Eurasian watermilfoil) was determined using surface observations and rake tows. Areas of milfoil identified between sample points were also noted and used to delineate larger beds of milfoil where appropriate. Modified acreage grid analysis was used to estimate the area of each plant bed.

Survey Results

Figure 2 shows the results of the October 2010 survey of Chute Pond. There were a total of 77.8 acres of milfoil mapped during this survey. The density of milfoil in the areas indicated, varied from sparse to very dense. In previously treated areas, such as the southwestern part of the lake, either no milfoil or very sparse milfoil was found. In some newly identified areas, such as beds C and E, milfoil was dense enough to interfere with navigation. Curly-leaf pondweed was only found at a couple of locations in the upper stretches of the flowage. This is to be expected as curly-leaf pondweed is a cold-water species, and due to its life cycle, dies back in the summer only to return in the spring. A spring survey is a better assessment of curly-leaf pondweed abundance and distribution. No other exotic species were identified during this survey.

Conclusions and Recommendations

The trend over the past couple of years suggests that chemical treatments appear to be successful at controlling milfoil in the areas treated. New areas have been found in each of the last two surveys, and these new areas make up much of the total area of milfoil present in the lake. In terms of the distribution of Eurasian watermilfoil, overall there was a 28.9% decrease from 2009 to 2010.

As seen in the past year, Chute Pond has ideal conditions for Eurasian watermilfoil to thrive. The plant has shown that it can quickly spread and achieve high densities that impede navigation. This can be attributed to the lake’s shallow, fertile waters, and high amount of boat traffic that can cause the plant to spread around. It is important that the District stay proactive in the management of the plant, since it has the potential to grow just about anywhere in the 433 acre lake.

Although progress has been made in the treated areas of Chute Pond, the newly discovered locations pose additional threats to the lake. Since the chemical treatments have yielded positive results, it is recommended that all locations of milfoil again be treated if funding is available. If the full distribution of milfoil cannot be treated, a prioritized list of locations can be developed to effectively treat the areas of highest need.

Attention should also be focused on slowing the spread of milfoil further to the northern portions of the lake. This area poses difficulties for treatment due to the shallow, flowing water, and abundant stumps and snags. Since the water is continuously flowing in this area, it is likely the milfoil was introduced by boat traffic. District members should stress to lake users the importance of keeping boats clean of milfoil. Besides emphasizing clean boats within the system, it should also be a focus at the boat landings. This will help reduce the chance of any new exotic species entering Chute Pond, as well as reduce the chance that milfoil from Chute Pond spreads to other lakes in the area.

Since a large portion of the remaining milfoil was found in the upper sections of the flowage, it is recommended the water levels not be adjusted for the 2011 treatment as they were in the spring of 2010. Although higher water levels reduce the extent of dilution following a treatment, they also facilitate navigation in shallower areas containing milfoil. This tradeoff is reasonable in the efforts to gain long-term control of Eurasian watermilfoil

Because of the ability of Eurasian watermilfoil to spread within this water body, it is recommended that annual surveys be performed to find any new locations of milfoil before they reach nuisance levels. With the wide-spread distribution of milfoil in the lake, it is recommended that the point-intercept survey methodology continue to be employed to accurately locate and map milfoil in Chute Pond.

Finally, the District should consider again postponing all cutting activities in the lake while Eurasian watermilfoil management is ongoing. If the distribution of milfoil is reasonably reduced, cutting can resume in some areas. However, with the risk of spreading milfoil associated with cutting activities, it would be in the District’s best interest to wait. Understandably, this may pose problems with the shoreline residents. Board members will need to decide on the best course of action regarding cutting operations in 2011.

Brad Roost, Limnologist
Cason & Associates, LLC
P.O. Box 230
Berlin, WI 54923-0109

office: 920-361-4088
cell: 920-420-2077
fax: 920-361-4086

http://www.casonassociates.com
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