HYDRILLA SHOWS INCREASED TOLERANCE TO FLURIDONE AND ENDOTHALL IN THE WINTER PARK CHAIN OF LAKES: CONSIDERATIONS FOR RESISTANCE MANAGEMENT AND TREATMENT OPTIONS Amy L. Giannotti & Timothy J. Egan - City of Winter Park Michael D. Netherland, Ph.D. – USACOE Marissa L. Williams – City of Maitland Alicia K. Knecht - FFWCC • Resistance theory • History of WP Chain hydrilla & resistance development • Irrigation study
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HYDRILLA SHOWS INCREASED TOLERANCE TO FLURIDONE AND ENDOTHALL IN THE WINTER
PARK CHAIN OF LAKES: CONSIDERATIONS FOR RESISTANCE MANAGEMENT AND TREATMENT
OPTIONS
Amy L. Giannotti & Timothy J. Egan - City of Winter Park Michael D. Netherland, Ph.D. – USACOE Marissa L. Williams – City of Maitland
Alicia K. Knecht - FFWCC
• Resistance theory • History of WP Chain hydrilla
& resistance development • Irrigation study
What IS herbicide resistance? Susceptible – control achieved using normal use-rates
Tolerant – never controlled at label use-rates
Resistant – originally susceptible; but over time, control is lost as resistant plants survive; repeated product failure
*Multiple resistance – resistant to herbicides with different modes of action (MOA)
Lake Minnehaha, July 2007
Resistance – how does it happen?
Susceptible Semi-Resistant Resistant
Naturally resistant plants exist within the population
Resistant plants survive the treatment
After regrowth, percentage of resistant strain increases
With repeated use, resistant plants become dominant strain
Minnehaha
Maitland
Osceola
Mizell
Virginia Berry
Sue
Killarney
I-4
N
Navigable Canal
Stream Inflow
Stream Outflow
Outfall Weir
Orlando
Win
ter
Par
k C
hai
n o
f L
akes
No barrier
City of Winter Park
Lake Osceola c. 1968
Lake Virginia c. 1968
• 28,000 residents • 600+ lakefront homes • 23 lakes and ponds • Aquatic plant management
activities since 1960’s
• Residents irrigate from the lakes • Keeping residents informed
about lake management efforts is essential
Challenges affecting hydrilla management Deep lakes = $$$ treatments
Average depth of Lake Maitland = 13.5’, Killarney = 14’
Average sale price of lakefront homes 2011-2013 - $2M
“Open” system/no carp barrier on north end
Migratory bird population affects carp stocking
Extensive ornamental landscaping Residents accustomed to irrigation
restrictions <14d “New” systemic products have
irrigation restrictions in excess of 30 days (concentration-based/up to 120 days)
Diverse and abundant native plant community Alum injection, stormwater infrastructure,
street sweeping, active public education 2,300+ inlets, 46 miles of pipe treat 17 mi2
land
What is happening in Winter Park and WHY?
1960s – relied on mechanical harvesting
1970s-1990s – infestations intensively targeted with Hydout (endothall)
1990s – Sonar (fluridone)
2007 – fluridone discontinued after multiple failed treatments
2008 – lakes stocked with low rates of triploid grass carp; widespread spot-treatments with endothall
2009 – entered FWC state-funded program
Late 2009/early 2010 – two failed whole lake endothall treatments; **first documented case of endothall resistance (Lakes Maitland & Minnehaha)
Multiple Resistance – fluridone and endothall
Susceptible Semi-Resistant
Resistant
With repeated use, resistant plants become dominant strain
Maitland Minnehaha • Reliance on Hydout in the 1970-
80s
• Last fluridone treatment was in 1998
• Discontinued use of fluridone in
2007 after repeated double upstream failures; spot-tx endothall with mixed results (temp?)
• Stocked with TGC in 2008 • 2009 - Failed WLT w/ endothall
- **documented resistance • Implemented combo tx,
bumped carp stock, & emphasized rotation
• Limited by irrigation
restrictions for new products
• 1990s – managed by WP
• Frequent turnover of City lakes staff delayed problem recognition w/ fluridone
• Discontinued use of fluridone
in 2007 after repeated failures; spot-tx endothall with mixed results (temp?)
• Stocked with TGC in 2008 • 2010 - Failed WLT w/ endothall
- **documented resistance • Implemented combo tx,
bumped carp stock, & emphasized rotation
• Limited by irrigation
restrictions for new products
2013 – both lakes still resistant to
fluridone and endothall
Lake Maitland – 6 WAT – Feb. 2010
WLT- Aquathol K Dec. 16, 2009 – 436 acres Applied in blocks at 3 ppm in littoral zone Lakewide concentration of 1 ppm Targeted lethal rates achieved > 1 ppm for 3 DAT > 0.75 ppm for 6 DAT
Irrigation – 1” of treated water once a week, along with one supplemental watering
No fertilizer or weed control
Pallets/concrete block as plant holders
Randomly distributed
Full exposure to sun and rain
Stock solution & treatment concentrations confirmed via Dr. Netherland throughout
BOTH are used at low rates and require extended exposures for effective
control. However, these herbicides break down slowly which results in
long-term residual exposures (90d+) in the water column.
Bispyribac – 13 WAT (0 ppb & 320 ppb) Ile
x V
ibur
nu
m
Liri
ope
Pod
ocarpus
Spa
rtina
0 ppb 0 ppb 320 ppb 320 ppb
Penoxsulam – 13 WAT (0 ppb & 320 ppb)
0 ppb 320 ppb 320 ppb 0 ppb
Ilex
Spa
rtina
P
odoca
rpus
Vib
urn
um
Li
riop
e
No apparent effect on growth and/or survivability of these 5 species with either product
Some treated plants seemed to exhibit weed control
Bispyribac & Spartina @ 4 WAT Penoxsulam & Podocarpus @ 6 WAT
ONLY looking for survivability - did not control for rainfall, soil type/amount, initial plant age, grazers, etc.
Based upon these results, Winter Park will incorporate these herbicides into our treatment regime after an intensive public education campaign
Our findings
Does NOT result from a chemical-induced change in plant genetics
Theory: every plant species has biotypes
that are resistant to every herbicide (true of many pests in nature); these “resistant biotypes” can be exceedingly rare and are not necessarily a component of every population in a lake.
“Applicator Roulette” – each population in
each lake has a varying degree of genetic diversity/biotypes present
***Has THAT biotype been sprayed yet? With what, how much, and how often?
ROTATE, ROTATE, ROTATE…..
7 WAT, Aquathol K, Feb 2010
Resistance Summary
www.cityofwinterpark.org/lakes
Thanks for hanging around!
Acknowledgements: City of Winter Park Lakes Division & Parks and Rec Matthew Malloy UF/IFAS Staff
Jeremy Slade Applied Aquatics Ryan Moore
Orange County EPD Dharmen Setaram City of Maitland Lakes Staff