big watab lake: aquatic invasive plant sentinel survey...during the late-spring aip sentinel survey,...

AIP Sentinel Survey – Big Watab Lake (Stearns Co.) – June 2016

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Big Watab Lake: Aquatic Invasive Plant Sentinel Survey

Stearns County, MN (WBIC# 73-0102) Surveyed June 13, 2016 Survey, Analysis, and Reporting by: James A. Johnson – Aquatic Ecologist, Freshwater Scientific Services, LLC

Prepared for Big Watab Lake Association – June 2016

15771 Creekside Lane Osseo, MN 55369 [email protected] (651) 336-8696



Survey & Analysis Methods

Late-Spring AIP Sentinel Survey Freshwater Scientific Services, LLC completed a lake-wide search for aquatic invasive plants (AIP) in Big Watab Lake (#73-0102) on June 13, 2016. This first of two planned surveys in 2016 was timed to coincide with the typical peak abundance of curlyleaf pondweed (CLP), but we also searched for other submersed and emergent invasive plants such as Eurasian watermilfoil, starry stonewort, and flowering rush, as well as invasive shoreland plants such as narrow-leaf cattail and purple loosestrife. A second survey is planned for August to once again search for aquatic invasive plants during the typical period of peak abundance for Eurasian watermilfoil or starry stonewort. During this late-spring survey, we navigated a meandering search-path over portions of the lakes that were shallower than 15-ft, including two submerged islands. While navigating this search-path, we used a combination of surface observations (using polarized sunglasses), sonar readings, and rake tosses to locate and delineate any areas with invasive plants. Sonar and visual assessments were conducted continuously, with subsequent rake tosses at ~150 locations where plants could not be seen or identified from the surface. At each location where we found invasive plants, we used a hand-held Garmin GPS unit (GPS-MAP78) to record the location, and then documented water depth, plant height, and plant abundance (rake density rating; 1 to 3 scale as described below). Density Ratings

We entered these recorded locations, water depths, plant heights, and rake densities into desktop GIS software and projected results over aerial imagery of the lake. We then delineated beds of invasive plant growth (for each species found) and calculated the area and mean rake density within each of the delineated beds. During the late-spring AIP sentinel survey, we found two invasive plants: curlyleaf pondweed (Potamogeton crispus) and narrow-leaf cattail (Typha angustifolia). We did not observe any purple loosestrife on shore (not yet flowering), but lake residents have reported that there are a few areas of purple loosestrife as well. The maps on pages 3 and 4 provide additional information on the location and extent of these invasive plants.

Score Visual Rake

1 Light Nuisance / Solitary Plants 1-2 stems

2 Moderate Nuisance / Dense Patches 3 to 9 stems

3 Severe Nuisance / Matted growth 10+ stems

Findings



15771 Creekside Lane Osseo, MN 55369 fixmylake.com (651) 336-8696

Map produced for Big Watab Lake Association by:

Surveyed: June 13, 2016 Survey/Analysis: JA Johnson Methods: Visual, Sonar, Rake

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Big Watab Lake (#73-0102) Aquatic Invasive Species – Sentinel Survey: June 13, 2016

AIS Survey Results

1 2

3

Curlyleaf Pondweed Rake Density Rating (0-3)

Search Path (7.0 miles)

Narrow-leaf Cattail (Typha angustifolia)

Present near shore



2

1

3

Surveyed: June 13, 2016 Survey/Analysis: JA Johnson Methods: Visual, Sonar, Rake

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Big Watab Lake (#73-0102) Aquatic Invasive Species – Sentinel Survey: June 13, 2016

Plot

Area (acres)

Mean Density (0-3)

Mean Depth (ft)

1 0.43 2.1 5.6

2 0.29 2.0 7.5

3 0.24 2.1 7.0

Total 0.96

Curlyleaf Management *

Potential Herbicide Plots

Potential Hand-Pulling

* See page 5 for a detailed discussion of management options

15771 Creekside Lane Osseo, MN 55369 fixmylake.com (651) 336-8696

Map produced for Big Watab Lake Association by:

1 2 3

Curlyleaf Pondweed Rake Density Rating (0-3)



Management Context

Curlyleaf Pondweed Curlyleaf reproduces and spreads primarily through the formation and deposition of vegetative buds called turions. These turions look like little pine cones and each individual plant can make roughly 10 to 20 new turions each year. Curlyleaf can also make seeds, but these are though to be less important in the annual life-cycle of the plant. The typical annual life-cycle of curlyleaf pondweed begins with sprouting in the late summer and early fall from previously deposited turions. These sprouts persist under the ice during the winter, and then grow rapidly as waters warm after ice out, typically reaching the water surface in late May. At this time, the plants begin forming new turions. Shortly after turions are formed (typically in June), the curlyleaf plants naturally die back and deposit their new turions to the lake sediment. Some fragments with attached turions may also drift to other areas of the lake, thus spreading the infestation, but most turions appear to be deposited close to where they were produced. This repeated deposition of turions to the same area year after year can lead to a buildup of turions that can eventually lead to dense, surface-matted growth. Because curlyleaf acts like an annual plant (new sprouts from turions each year rather than regrowing from old roots), the key to managing this plant is to interrupt the annual production of turions. This can be accomplished by cutting or hand-pulling smaller areas of curlyleaf, or by treating larger areas with herbicides in the spring before new turions are formed. Currently, the preferred strategy is to treat curlyleaf with endothall herbicide in the spring when water temperatures are between 50°F and 60°F. Below 50°, the herbicide is less effective at killing curlyleaf, and above 60°, many of the native plants have sprouted and may be damaged by the herbicide. Given that the water temperature in Big Watab is already above 60°F, we need to consider a different approach for managing the curlyleaf this year. The plants have just begun producing new turions, so time is of the essence. There are three management options: (1) Manual removal of curlyleaf plants (hand-pulling by divers, cutting) (2) Treat areas of curlyleaf with a fast-acting contact herbicide like diquat (3) Do nothing in 2016 and just plan to treat the areas with endothall in the spring of 2017 Manual Removal The total area of curlyleaf (roughly 1 acre) is fairly large for manual removal. This would require a substantial amount of work by volunteers or a substantial expense if divers were hired to pull the plants. The DNR allows manual removal of plants from up to 2500 sq-ft for each lake property without having to apply for a permit. The areas of curlyleaf span across multiple properties, so it may be possible to remove most of the curlyleaf without a permit, but the lake association should contact the DNR to discuss whether a permit is needed. Herbicide Many lakeshore homeowners hire herbicide applicators to kill plants around their dock each year. For such treatments, applicators typically use a fast-acting contact herbicide (such as diquat) to kill all plants in a small area. This requires a general Aquatic Plant Management permit, but is a very common practice on many lakes. Consequently, this would likely be the easiest, fastest, and least expensive method of minimizing turion production and drift in 2016. For these reasons, this is the method that I recommend for 2016. Given the small areas that would be treated, the impact to fish habitat and the lake would be minimal. Do Nothing This should always be considered as an option in plant management. However, given that this is a new curlyleaf infestation that is very localized, I do not recommend option 3.



Management Context

Narrow-Leaf Cattail

Although this is considered to be an invasive plant, you should not be overly alarmed about having it on your lakeshore. This plant has replaced our native wide-leaf cattail throughout much of Minnesota, but most lake residents never noticed the shift from native cattail to invasive. This shift has generally reduced the quality of the cattail habitat for wildlife due to its dense growth. Furthermore, narrow-leaf cattail is less sensitive to changes in water level than our native cattail, allowing it to grow out into slightly deeper water in lakes where water levels fluctuate seasonally. This can lead to noticeable expansion of the invasive cattail beds in shallow bays. Given the steep dropoff along much of the shoreline in Big Watab Lake and the relatively stable water level, the problems caused by this plant should be minimal.



Online Resources & Contacts

Minnesota Administrative Rules for Aquatic Plant Management https://www.revisor.mn.gov/rules/?id=6280 Minnesota DNR – Aquatic Plant Management Regulations & Permit Application Forms http://www.dnr.state.mn.us/apm/index.html

Christine Jurek Invasive Species Specialist Minnesota DNR [email protected] (320) 255-4279 (ext 232) Chip Welling AIS Management Program Coordinator Minnesota DNR 500 Lafayette Road Box 25 St Paul, MN 55155-4025 [email protected] (651) 259-5149 Steve Enger Aquatic Plant Management Program Coordinator Minnesota DNR 500 Lafayette Road Box 25 St Paul, MN 55155-4025 [email protected] (651) 259-5092

big watab lake: aquatic invasive plant sentinel survey...during the late-spring aip sentinel survey,...

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