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’

Excellent urban fishery Highest overall largemouth bass catch

rate in any central FL creel since 1999

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

Lake 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 (Sept)

Virginia 225 ac

7 11 W/27 98 W/15 50 2 1 0 7 11

Mizell 62 ac

W 0 14 6 10 31 0 2 0 1 1

Osceola 156 ac

W <1 11 29 41 99 26 83 54 3 0

Maitland 436 ac

2 <1 3 4 37 216 W/366 66 169 10

3

Minnehaha 95 ac

0 6 W 20 W/45 44 49 W/27 23 3 2

Berry 76 ac

3 2 W 0 14 7 12 35 31 0 0

Killarney 240 ac

<1 2 7 30 W/16 0 0 0 3 29 109

Total 13/ 2 W

23 62/ 3W

187 178/ 3 W

447 455/ 1W

309/ 1W

280 53

126

BLUE = failed high rate fluridone treatment

RED = failed low rate fluridone treatment

PURPLE = failed endothall treatment

= Carp stocked

Thankfully, our best defense… …is a good offense

So, now what?

Maitland and Minnehaha hydrilla produce higher levels of protein phosphatase, which endothall normally

inhibits….so having more enzymes means this biotype can tolerate higher levels of endothall.

Since then – 5 combinations utilizing 3 different MOA & increased reliance on grass carp

1) Diquat, 2) Endothall+diquat, 3) hydrothol, 4) flumioxazin, 5) imazamox 6) bispyribac (2014) 7) penoxsulam (2014) Fluridone resistance still an issue

Bumped carp stocking rate

Hydrilla leaf miner & Mt fungus (2013)

Modes of Action (MOA) for Hydrilla Herbicides

• Diquat – PS Inhibition • Fluridone –

carotenoid/pigment/chlorophyll disruption

• Flumioxazin – captures energy and destroys cell membrane

• Endothall – UNDEFINED • Imazamox – ALS inhibition* • Bispyribac – ALS inhibition* • Penoxsulam – ALS inhibition* *but different chemistries

involved

Endothall’s MOA is not specific to any particular plant

process, which is unlike other compounds used for hydrilla control

Current Focus: New herbicides FWC encouraging herbicide rotation for resistance

prevention & wanted WP to include all new products into our management program

Public hearings Lakes and Waterways Advisory Board

City Commission

Newsletter articles Multiple issues

Website

Direct mail General to all lakefront homes

Specific treatment notices

Winter Park needed to address likely public concern over using new systemic herbicides

New products have irrigation restrictions up to 120 days

Historically, residents accustomed to < 14 day restriction

**Impacts on terrestrial landscaping are not well understood

City Commission & USACOE supported in-house irrigation experiment to evaluate

Information and time provided to decide whether or not to employ alternative irrigation sources

Concerns

Reaction to the last 14+ day restriction…

And even the industry reps

were concerned…

Experimental Design 12 weeks

240 plants

5 common landscape species Japanese yew (Podocarpus spp.) Sand cordgrass (Spartina bakeri) Viburnum (Viburnum spp.) Burford holly (Ilex cornuta burfordii) Border grass (Liriope spicata)

2 herbicides – bispyribac & penoxsulam

8 treatment rates 0 ppb, 5 ppb, 10 ppb, †20 ppb, *40 ppb, 80 ppb, 160 ppb, 320 ppb * = bispyribac target; † = penoxsulam target

3 replicates for each rate

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