Dr. Pullman's Response To Weed Treatment Questions

Prophylaxis and Limits on Agent Activity:  One common misconception is that the registered aquatic herbicides can provide prophylactic control of targeted weed species.  This is not true.  In fact, the “active phase” of the registered aquatic herbicides used for submersed weed control is measured in terms of hours.  This should not be confused with how herbicide residuals are calculated, because residuals are estimated in a manner that does not necessarily reflect the period of herbicidal activity associated with the agents used.  Aquatic herbicides and algaecides are quickly sequestered by plants, algae, and other microbes or they are rapidly transformed to inactive compounds and forms by reactions with the chemical constituents in the water or suspended sediments.  Basically, all beneficial activity occurs soon after application and does not extend more than hours from the time of treatment.  This is why we ask that people stay away from treatment areas so as to not stir up the sediments that will interfere with the control agent activity and ultimately the treatment outcomes.  Furthermore, aquatic herbicides and algaecides have virtually no impact on seed and only marginal impacts on plant parts in and around the sediments.  They don’t kill seed and can’t “get to” or impact plants associated with the sediment “regions” at the bottom of lakes.  The degree of impact is also related to the metabolic activity of the target plants.  An actively growing plant is far more susceptible to the herbicides than are plants that are compromised by weather or natural cycles such as normal late season decline, that render them less metabolically active.  All this means that any successful treatment must be applied to actively growing plants when surface and sediment temperatures align to provide a reasonable expectation of meeting the desired objectives.  Plants that become metabolically active or emerge from seed or the sediments a day or two after treatment will see no effect.  That means that an ill-timed treatment or one done before optimal application times may see only immediate impacts that are subsequently lost to emerging weeds from seed and protected structures.

Temperature Impacts on Treatment Outcomes:  Spring and early summer warming has a dramatic impact on treatment efficacy.  Generally speaking, the later in June that a lake in Michigan is treated, the better the treatment outcome and the greater chance that weed-free conditions can be maintained until the end of the recreational summer.  Studies have demonstrated that most of the aquatic herbicides can work at lower temperatures, but that efficacy diminishes with lower temperatures.  Consequently, the greatest barrier to success is associated with how the agents disperse in the water where there are different temperature layers.  The temperature differentials between surface waters and the sediments can significantly restrict the dispersal of control agents in the treatment zones and seriously compromise the effect of treatment.  As oe example, warm herbicides applied to sunbaked and warm surface water will drift off site without moving downward to the colder waters at depth that surround most of the target weeds.

Rapid or Explosive Weed Growth:  The worst weeds grow very fast.  Watermilfoil, starry stonewort, and curly leaf pondweed can grow inches in a single day and that means that any of these species can go from being nearly inconspicuous to “hay field” conditions in much less than a week.  There are obvious ecological benefits associated with explosive weed growth, but these are not detailed here.  It is unfortunate that there are no prophylactic treatments for these weeds since they can appear as acute nuisances so quickly.  It is also critical to note that FIFRA rules (federal statutes regulating pesticide use) prohibit applying agents to areas where the target plant cannot be observed or be expected to respond to the application of said agent since that would be inconsistent with the federal labels that appear on aquatic herbicides.  In practical terms, riparians will see weedy conditions before action can be taken because the treatment needs to be focused on growing plants and plants do not grow at the same pace throughout inland lakes.  The objective the Lobdell Lake Vegetation Management program is to minimize the extent of those times when nuisance conditions emerge in the lake and that may mean that some areas my present weedy conditions while the plants in other areas are beginning to enter the rapid growth phase that is critical to support successful treatment outcomes.  Logistically, this means that some areas my experience undesirable nuisance conditions on a short-term basis until it is time to pull the trigger on treatment.  Spot treatments do not provide good outcomes, so it is far more beneficial to wait until larger areas become susceptible to the impact the agent applications.  Otherwise, treatment outcomes may fail to mitigate nuisance conditions, if the treatment zones are too small.

Weed and Plant Community Composition:  Every year is different and the dominant weeds that afflict Lobdell Lake (and others) vary each year.  Since different plants and weeds respond quite differently to different herbicides and algaecides different agents and agent combos are used each year to address the specific and critical weed issues that emerge each individual year.  Reviewing the management history of Lobdell Lake it is rare that the same herbicide combos are used each year since the weeds vary in specific composition and ratios so much from year-to-year.  Effective weed management programs are necessarily adaptive!  LakeScan™ monitoring provides an empirical basis to evaluate the impact of management efforts and suggest alterations to the program when necessary.

Weed Management Program and Objectives:  The Lobdell Lake Vegetation Management program is focused on the suppression of weeds and support of desirable plant species.  This is consistent with the goal of providing a stabile and desirable ecosystem that will support a wide range of needs and recreational opportunities.  Weeds number from 3 to 5 species out of the nearly 30 species observed each year.  The management team reviews conditions prior the Memorial Day each year to estimate the extent of a first of season treatment that is usually focused on varying proportions of nuisance watermilfoil and curly leaf pondweed.  Sometimes, other weeds will emerge and these too will be addressed after consideration by the management team.  The team also considers weather patterns and attempts to estimate when sediment temperatures reach approximately 65˚F as a target time of application.

Typically reasonable conditions for successful weed treatment occur around the first week of June in Lobdell Lake.  Again, only actively growing plants respond to treatments that occur and then, the herbicides only perform well when water temperatures have reached an adequate level to support successful outcomes.  By the time of the year that water temperature dynamics allow for reasonable expectations for successful treatments, watermilfoil and curly leaf pondweed have already reached serious nuisance levels in many parts of the lake.  Again, this is because water temperatures can seriously compromise herbicide efficacy.  I’ve attached a table that documents when treatments have been applied to the lake for the past 10 years.  I also reviewed data going back to 1988 and it is remarkable that the first major weed treatment of the year falls within the first week of June in most years.  We attempted to move the first major treatment of 2024 to the weed before Memorial Day, but all of the areas treated before the holiday had to be retreated at some point later in the season due to rapid regrowth of offending weeds.  Interestingly, a secondary treatment applied just 10 days later, but after Memorial Day provided nearly summer long control of weeds in the areas where the later treatment occurred.  This is compelling evidence that the first week of June remains a viable target for the first major treatment of the season and that it may be fiscally and practically irresponsible to attempt to treat the lake earlier than Memorial Day.

Late Season Treatments:  One of the objectives of the management program is to maintain relatively weed free conditions from the time of the first major weed treatment in June until the following Labor Day.  The accompanying table shows that each year has been different.  In some years the treatment effect and weather conditions conspired to provide relatively weed-free conditions until Labor Day and no August treatment was needed.  In other years, August treatments were needed to provide good conditions for the remainder of the season.  If weed-free conditions are not maintained until the late summer as a consequence of the first major treatment, it is known and expected that there will be a period of time from when the weeds first become conspicuous to when the treatment can occur.  Late season watermilfoil growth can begin in late July, but nuisance conditions are not usually observed until mid-August, if the first major June treatment and weather contribute to the emergence of late-season weed conditions … which is not always the case. 

The lake resident management team member (AJ) begins to assess the need for a late season treatment in July through direct observation and communications with other lake residents.  Mobilization for an August treatment is accompanied by some logistical challenges.  The State of Michigan restricts the use of what are often “first choice” cost-effective and efficacious contact herbicide mixtures after the middle June in areas that are greater than 5’ water depts or more than 100’ from shore, whichever is the smaller of the two areal restrictions.  Nuisance weed production in Lobdell Lake does not stop at the 5’ contour or areas less than 100’ from shore!  Some systemic herbicides are allowed under normal permit rules, but these agents are generally slower acting and given how rapid weed growth can occur and that the objective is often to provide weed-free conditions near the Labor Day holiday it is undesirable to use an agent that may fail provide relief in a rapid fashion.  Permit amendments that would allow the application of rapid action agent combos can be requested from the State, but this can add one or two weeks to time of treatment.  Amendments are not granted unless the State is assured that the level of nuisance conditions observed in the lake merits treatment and are not issued any earlier or in an anticipatory fashion.  This is because late season treatments may not be needed to maintain low nuisance conditions, and this would seem reasonable after review of the following table where August treatments were not needed in many of the years where the records are presented.  Control agent availability can also be a logistical challenge.  Aquatic herbicide suppliers generally try to reduce inventories near the end of the season.  Since the dominant weeds change each year, it is impossible to predict what agents may be needed, in what proportions, to mitigate possible late season weed production. Weeds are a moving target!  For example, there were significant delays in obtaining critical agents to facilitate the August 2024 treatment because of limited agent availability.  These agent accessibility issues resulted in delays of nearly two weeks and required that the treatment be split between to separate treatment events which impacted and extended water use restrictions on the lake.  A variety of agents were used to navigate the availability issues and evaluated the longer-term impacts of different management approaches.

Regarding your specific questions:

·       Weed Treatment Scheduling - a few people are concerned about the status of weeds in their specific area of the lake (Lobdell). They have asked two specific questions:

o   If we are having weed growth issues and we haven't spent our annual budgeted $ for weed treatment, why haven't we been more proactive in a 2nd or 3rd treatment?

o   There were concerns voiced about how late in the season the 2nd treatment is taking place. The question has been asked, 'why can't we schedule our 2nd and 3rd treatments in advance with you and the applicators and then 10 days out from the scheduled treatment develop a plan as to what needs to be done and/or cancel the treatment if all is in order'

Scheduling:  This is an issue in the spring and in the later part of the summer, so I’ll address both. 

Spring:  Weed treatment is executed when the weeds are present since there is no prophylaxis.  

·       The weeds must be metabolically active (growing) or the agents will have very limited effect.  

·       Lake water and sediment surface temperatures must be aligned to have any reasonable expectation of successful treatment outcomes.

·       Treatment agent combos must be adapted and adjusted to address the management objectives for the unique weed and plant communities that emerge each year.  Prudent management is not just about suppressing weeds, but encouraging growth of beneficial species that compete with weeds and stabilize ecosystems.

·       Management agent selection is restricted by permit and State rules and policies and agent combos are selected within the regulatory context.

We base treatment timing on “biology and weather” and given the above factors, conditions are generally favorable for treatment around the first week of June.

Late Summer:  Every effort is made to provide all-summer weed-free conditions all summer because the emergence of late season weed issues can persist for 10 days to two weeks before they are controlled.  In other words, a “good year” is where there is no outstanding weed conditions in the late summer.  We have seen this in a number of years.  But, weather and shifting plant communities often conspire to the production of weedy conditions in August.  Late season treatments are constrained by various permit policies and permit amendments are often needed to execute needed mitigation efforts.  High water temperatures and low oxygen concentrations can also be a problem for late season treatments.

You mention that one resident complained after a conversation with the ANC unit of EGLE.  

·       Nuisance Weeds - one of the members called EGLE and discussed the current situation with weed growth, especially vallisneria. He was told by EGLE that if the situation is deemed a "nuisance weed" impacting the use of the lake then the weeds can be treated regardless if they are native or non-native. Is this true? How should we respond?

The State holds the ultimate authority to define what is a nuisance through rule, policy, or statute.  Sometimes lake resident and regulatory definitions collide in a negative way.  The State does distinguish between invasive and native plants and they are treated differently according to permit policies. Currently, aquatic invasive species are defined as exotic or non-native species, and these can generally be managed with a somewhat restricted list of agents, anywhere in a Michigan inland lake.  However, the control of even these exotic nuance species can be further restricted if there are endangered species present or fishery concerns.  The MI EGLE ANC unit will permit the control of any nuisance weed depending on the species and location of the weed in the lake, but there are conditions.  So the statement as quoted above is correct – but there are restrictions!  Strict policies regulate what agents can be used and where and when those agents can be applied.  Any deviation from standard conditions requires additional action such as a permit amendment. For example, standard ANC permits allow the use of a broader range of control agents throughout the lake until June 15.  After that time and as stated previously, the use of rapid acting contact agents can only be used beyond the 5’ contour or 100’ from shore (whichever is the lesser area) and this only applied to areas that are adjacent to developed properties with an amended permit.  Permit amendment applications may or may not be approved and this may disappoint some resident groups because the State may not share the same definition of what constitutes a nuisance and therefore the need for treatment.  Permit amendment reviews may take longer than a week and delay the execution of management plans. The use of copper as an algaecide or means to enhance treatment outcomes is highly restricted and complicated.  Copper restrictions are a major factor in the selection of the control agents that may be used to achieve management objectives.

Technically, it is true that if the State concurs that a nuisance condition is present, it will allow treatment.  Treatment of nuisance native species is still restricted by policy.  The three exotic species considered as a common nuisance by regulators are granted relatively unrestricted treatment and the weeds can be treated throughout most of the lake at any time of the year.  However, the agents that can be applied to these species are strictly restricted depending on the time of the year.  Native species within the 5’ contour/100’ from shore region, and adjacent to developed properties are permitted for treatment throughout much of the year, but the more off-shore nuisance conditions are not usually permitted.  And, there are always fisheries concerns that may further restrict management even in these near-shore areas.  Sometimes it is possible to amend a permit to allow native plants to be treated in areas that extend beyond the near-shore areas.  An amendment request may not be approved based on the supporting arguments and how consistent the nuisance declaration is with agency policy.  The amendment process takes time resulting in serious delays in treatment.  There are significant restrictions on what agents that can be applied to the off-shore areas and these restrictions may compromise treatment outcomes.

There is still no known effective, consistent, or affordable way to manage the nuisance production of Vallisneria sp (Val).  Even if the State were to issue permits or permit amendments to address nuisance Val conditions, the technology simply does not exist to provide practical mitigation!  Lobdell Lake is now in year two of evaluations of various agent combos for the control of this pernicious weed.  It is hoped that some of these efforts may result in a practical solution to this common weed problem.

·       Some of the input was that we should spend every dollar of our annual weed treatment assessment budget to control weeds throughout the boating season. Thoughts? I think water temperature, etc. may impact this but would like your input

Lobdell Lake weed management budgets are carefully drafted and provide adequate resources to maintain good lake conditions and address conditions that may suddenly emerge as a consequence of the introduction of a potential “new” exotic invader.  Fortunately, nuisance mitigation strategies are generally not based as much on budget but rather what strategies work and will meet management and maintenance objectives in Lobdell lake.  Weather, water quality and temperature, species present and community dynamics, and regulatory considerations are the primary factors that are used to set management objectives and the adopt the strategies deployed to meet those objectives.  Monies expended each year depend on what the nuisance conditions are each year.  Some reserve is set aside to protect the lake from the possible invasion of new invasive species.  Some lakes are severely constrained by budgets, but the administration of the Lobdell Lake weed control program has done an outstanding job of planning for more present needs and keeping reserves for when new challenges arise.

Despite our best efforts to make limnology “understandable” we simply cannot avoid the fact that lakes are not “simple”. They are complex, and in a manner similar to human medicine or organismal biology, they require complex and adaptive consideration to maintain stability, sustainability, and favorable conditions.  Strateiges cannot be developed and executed on a calendar basis because biology does not function that way.  There are significant limits to what can be accomplished with the available technology used to manage weeds and the serious regulatory constraints that can delay and compromise management and maintenance programs.  I trust that this answers the questions that you posed.  Do not hesitate to call if you have further question.

G. Douglas Pullman, Ph.D.

Aquest Corp