Curley-Leaf Pondweed Update
Former SLA President Scott Alexander, is the Chief Geologist at Darcy Solutions. Scott is SLA’s resident expert on the science of Square Lake water quality, and AIS risk management. We are grateful to Scott for his scientific expertise, experience, and SLA legacy.
Lynn Mecum and I recently asked Scott to update us on curly-leaf pondweed treatment plans on the south side of Square Lake.
In the context of that discussion, Scott kindly shared two documents with information on the Square Lake plant communities, for your information:
1) Square Lake Plant Communities, dated 2019.
2) Square Lake Plants, dated 2021.
Scott also directed us to the US Army Corps of Engineers’ guide to wetland plants and plant communities, for those of you interested in learning more about the science of Square Lake.
Scott and Matt Mattson continue to monitor the patch of curly-leaf pondweed (CLP) on the southwest side of the lake, which is costing our Association an annual expense to hold in check, in some years exceeding $1700 per season.
In 2023, the Carnelian Marine St Croix Watershed District have generously offered to cover half of SLA’s curly-leaf control costs, and we are assessing whether to continue the treatment program.
According to WCD’s Matt Dowling, “On July 18, 2022, the WCD conducted an AIS Early Detection survey on Square Lake. A whole lake meander and 10 survey points were assessed from boat. Additionally, two hours of staff time were spent on targeted snorkeling of high-risk introduction areas. These efforts are in conjunction with the weekly early detection surveys that occur throughout the summer and the watercraft inspection program.
During this survey, no new AIS infestations were noted. Anecdotally, it does appear that areas of the lake are becoming less diverse for the native plant community, this may be something to watch for potential introduction sites as they are more susceptible to invasive establishment.”
In response to our clarifying questions, Matt further responded, “When native plant communities experience disturbance or degradation, they are more susceptible to aggressive species filling in. Some of the best defense to invasive species is a robust native community, with more diversity being more resilient to impacts that may on affect one or two species. This is true in an aquatic system, forest or even a roadside ditch.
My comments were based on observations that there are areas of the lake that are becoming a monoculture of Chara (muskgrass). While this is not immediately concerning, it is a shift from a more diverse community and may be due to pressures on the lake.”
In 2022, Scott and SLA’s Board received a commissioned report entitled and linked here Square Lake CLP Survey & Assessment, prepared by EOR Consulting.
After sharing the report with WCD’s Matt Downing, he commented, “This report does a great job detailing that the lake is healthy and not a high risk for further CLP invasion. The robust native plant community and high-water quality are noted as keeping the CLP growth limited.
What is the goal of any treatment efforts? CLP removal is not going to change the vegetation density in that area treated, as noted in the text and in Figure 2. Density is low, complete eradication is not a documented feasible outcome so best-case scenario for that is typically where Square Lake is currently.
The CLP levels are relatively low. There also seems to be some correlation with treatment encouraging expanded growth (Table 1). I would be interested to see if a few years of tracking without doing treatment show a different trend. Both Diquat and Endothall are contact herbicides that will have by-kill of native plants. This may be having a negative impact of creating more space for CLP to fill.
I would point out that this memo is written by a consultant who may have sound advice but is in the business of making money. Both statements for and against are made regarding efficacy of continued treatment.”
In Scott’s words, “The bottom line is that the CLP patch remains about the same whether it is treated or not. The CLP has a toe hold in the lake but does not seem to be able to out compete the native vegetation.”
Scott and Lynn have suggested conducting an aquatic plant tour of the lake on Memorial Day, for interested members. If you’re interested in participating, please contact Lynn.
In further response to our clarifying questions, Scott kindly shared his answers below:
Who is the source of handwritten 2021 notes in the linked Square Lake Plants presentation? Answer: Scott Alexander.
Is floating leaf pondweed, the same as curly leaf? Answer: The floating leaf pondweed is a different and quite native species from the curly-leaf pondweed (CLP).
If so, is that what we see in the green floating mat on the south side of the lake – or is that Chara – which I understand may not be invasive? Answer: The floating mats are Chara. Chara is a native species and is the dominant aquatic plant in most of Square Lake. It is not a rooted plant and is in fact an Algae. This is why the dense mats occasionally pick up enough air bubbles and lift up to the surface.
Assuming Chara is different from floating and curly leaf pondweed, which is considered invasive? Answer: Curly leaf is the invasive. Answer: Chara and the floating leaf pondweed are natives. There are also some mats of filamentous algae that also grow on the west end of the lake. These are not invasive but are slimy and obnoxious. Addressing the filamentous algae is a discussion about septic systems and manure handling.
In the past, what have you/Matt been treating with chemicals – the pondweed or Chara? Answer: All the previous treatments were for curly-leaf pondweed.
Understanding that CMSCWD will cover half the cost of treatment, what treatment, if any, do you recommend this year, and when – if the residents on the southside of the lake want us to continue the treatment? Answer: Treatment has not proven effective at reducing the curly leaf. When we haven't treated there has been no increase in CLP the next year.
When we first found the CLP, there was concern that it would spread rapidly around the lake. This has not proven to be the case.
We can almost certainly find more constructive things to do with the $2000 cost of delineation and treatment. And, despite the current frozen state of the lake we are already past the point where we could find someone to delineate the current CLP patch and lay out a treatment plan.
The point of doing an aquatic plant tour on Memorial Day would be to help show people what plants are normal and what is invasive.
The SLA Board thanks Lynn Mecum, Scott Alexander, Matt Mattson, Matt Downing, and Mike Isensee, for their continuing best efforts to educate SLA on AIS best management practices. The Board will decide whether to continue CLP treatment. If you have any questions, please contact Scott Alexander, Lynn Mecum, or Jim Seidl.