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Aquatic Invasive Weeds
Mark Sytsma
Center for Lakes and Reservoirs
Aquatic Bioinvasion Research and Policy Institute
Portland State University
Benton County CWMA Aquatic Applicator Short Workshop
Corvallis • 10 March 2016
Overview
Why manage invasive aquatic weeds?
Some common and not-so-common invasive
species (focus on the Pacific Northwest)
Options for aquatic plant management
Some nonplant invasive species to watch for
Introduction
Management of aquatic weeds is complicated because:
Many species are easily confused with native or legally imported species
Common names are confusing and often misapplied
Many aquatic weeds reproduce vegetatively from small fragments
Water moves
Aquatic systems contain many sensitive and endangered iconic species that complicate management
Algae
Microscopic
greens, diatoms, golden, dinoflagellates,
cyanobacteria
Nitella Chara
Ecological impacts
Reduce light penetration & mixing
Reduce species diversity
Alter temperature, dissolved oxygen & pH
Degrade fish habitat
Altered nutrient cycling can
lead to algae blooms and
toxicity
Impacts on biodiversity
Madsen et al. 1991
Food web and nutrient cycling
Carpenter and Lodge 1986
Economic impacts
Reduce flow in irrigation canals and drainage ditches Increased cost of irrigation
Flooding
Clogged pumps & intake structures
Loss of recreational resources
Negative impacts on property values
Human safety
Myriophyllum spicatum Eurasian watermilfoil
Feathery leaves divided into leaflets. 3 to 5 leaves grow in a whorled pattern around the stem.
When out of water, leaves lose their rigidity and collapse around the stem.
Easily confused with native milfoil species
Eurasian
watermilfoil Northern
watermilfoil
Myriophyllum spicatum x sibiricum Hybrid watermilfoil
Intermediate characteristics
Rapidly spreading in Great Lakes region
Increased resistance to several herbicides commonly used on EWM
Confirmed in Howard Prairie Reservoir & multiple sites along the Rogue River
Ke
v A
lexa
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n
Myriophyllum heterophyllum variable leaf watermilfoil, two-leaf watermilfoil, & red foxtail
Siltcoos Lake, Oregon
Present at 22 of 297 sampling
locations
Extensive monocultures in protected
bays
Class A noxious weed in Washington
5 lakes being treated
Hydrilla verticillata
Monecious biotype in Washington
(10yrs, $10M eradication)
Dioecious biotype (only female)
thermally-influenced Bruneau River,
Idaho
Endangered snail present
Diquat and handpulling
Hydrilla verticillata hydrilla, Florida elodea, water thyme
Egeria densa Brazilian elodea
Dioecious Only male plants outside native range in South
America
Dispersal by fragments only
Most common invasive aquatic plant in west-side lakes
Elodea canadensis/nutallii American waterweed, common elodea
Native species common throughout Oregon
R. V
id-k
i /
ww
w.b
ugw
oo
d.c
om
E. canadensis E. nutallii
Similarities in the Hydrocharitaceae U
SD
A P
LA
NT
S d
ata
base
Elodea
canadensis/nutallii
(native)
Egeria densa
(B-list noxious weed) Hydrilla verticillata
(A-list noxious weed)
Turions and tubers are features of hydrilla
Potamogeton crispus curly leaf pondweed
Common throughout Oregon
Turions form in spring on small plants, sprout
in fall and overwinter
Typically bimodal biomass curve – most
abundant in spring and fall, dies back in
summer
Long-term control requires interrupting turion
formation
Cabomba caroliniana
Appears to be
restricted to low-pH,
dystrophic (tea
colored) lakes
Easily confused with
submersed form of
water buttercup
(which has alternate
leaves)
Ranunculus aquatilus
gobota
ny.n
ew
engla
ndw
ild.o
rg
Ceratophyllum demersum coontail
Native
Not rooted
Bifurcated leaves
Inconspicuous,
submersed flowers
Duckweeds
Mail-Tribune file photo
http
://ww
w.ru
du
ckw
ee
d.o
rg/
duckweed
http://waynesword.palomar.edu/1wayindx.htm
Eichhornia crassipes water hyacinth
10 miles of thermally influenced Snake
River infested eradicated
Umpqua River infestation
Salvinia molesta salvinia
Cryptobagous salviniae
Annual releases of Cryptobagous salviniae on Lower Colorado R.
Source: Dewey Murray, USDA APHIS PPQ
Efficacy of Cryptobagous salviniae on Lower Colorado R.
Photos: Dewey Murray, USDA APHIS PPQ
2004 2005
Limnobium laevigatum South American spongeplant
• Redding pond (June 2005)
• 0.25 m2 quadrat: >2,000 plants
• Chokes out water primrose and parrotfeather; grass growing on the mat
• A-listed noxious weed in OR
Azolla pinnata feathered water fern
Federally listed noxious weed
Azolla filiculoides and A. mexicana
Natives
Nymphaea odorata fragrant water lily
Identification:
Rooted aquatic perennial
Grows in depths of 3-6 feet
Floating heart-shaped or circular leaves (30 cm); purplish underneath, leathery, slit in one side
Large (6-12 cm) fragrant flowers; 20-30 petals, range of colors with yellow centers
Seed and rhizomes
Nymphoides peltata yellow floating heart
Native to East Asia
A-listed noxious weed
Scattered populations in
southern and eastern OR,
and Portland metro areas
Bacopa rotundifolia disk water hyssop
Considered imperiled in neighboring states
Herbarium specimen in WY from 1891and from ID in 1933
First occurrence in Oregon in Columbia River in 2014
Weedy in rice fields in CA
What to do about it in Oregon?
Natureserve.org
Nuphar polysepala yellow pond-lily
NATIVE
Similar habitat
Larger, oval to heart-
shaped leaves with a
prominent midvein
Flowers – yellow
petals and centers,
9-petals
Brassenia schreberii watershield
NATIVE
Similar
habitat
Oval, peltate
leaves
Inconspicous
flowers
Phalaris
arundinacea
Lythrum
salicaria
Iris
psuedacorus
Yellowflag Iris Purple loosestrife Reed canary grass
Cattails
Typha latifolia
Native
Typha angustifolia
Invasive X Typha glauca
hybrid
Phragmites australis reed
ssp. americanus ssp. australis
Sagittaria spp.
Sagittaria
graminea Class B in WA
(3 locations)
Sagittaria
platyphylla (1 lake in WA/
Blue Heron Wetland,
Portland
Potential noxious listing)
Sagittaria
rigida Class B in WA
(6 locations)
Myriophyllum aquaticum parrotfeather milfoil
Native to South America
Only female plants present
Dispersal by fragmentation
Difficult to control
Ludwigia spp. Water primrose water primrose
Abundant in middle reaches of the Willamette downstream to
Columbia R.
Active control efforts underway
Delta Ponds, Eugene
Willamette (Willamette Riverkeepers)
Aquatic perennial
Moving down Columbia River from infestation in Montana
Large infestation in Yakima River
Suction harvesting of small populations near McNary Dam
Submersed and emergent growth forms
Dispersal by rhizome fragments
Butomus umbellatus Flowering rush
Spartina spp. Estuarine cordgrasses
• 4 non-native, invasive species
– S. alterniflora (Eastern & Gulf coast of North America)
– S. patens (Eastern & Gulf coast of North America)
– S. anglica (hybrid of English S. maritima & S. alterniflora)
– S. densiflora (South America)
• 1 native (S. foliosa)in California
• Hybrids
S. alterniflora
S. densiflora
S. patens
S. anglica
Known Spartina Distribution
on the West Coast Comox Harbor, BC
Fanny Bay, BC
Boundary Bay, BC
Puget Sound, WA
Gray’s Harbor, WA
Willapa Bay, WA
Columbia River
Sand Lake, OR
Siuslaw River, OR
Coos Bay, OR
Humboldt Bay, CA
San Francisco Bay, CA
Aquatic Weed Control Methods
Biological
Manual
Physical
Mechanical
Chemical
Biological Control Options
Purple loosestrife
Galerucella spp. (leaf feeding), Hylobius
(root) & Nanophyes (flower/seed)
Very successful – reduction in growth,
occurrence & competitiveness
Eurasian watermilfoil native weevil - Euhrychiopsis lecontei
Results difficult to predict (fish predation,
overwintering habitat)
Grass Carp (Ctenopharyngodon idella)
Generalist feeders – low/no selectivity
Very limited applications
“biological success” vs “impact success”
Manual Control Options
Hand-pulling, or underwater
weeding
Target specific weeds, move around
obstructions, minimal equipment
Labor intensive, creates murky water
and fragments
Rakes, cutters
Inexpensive
Labor intensive, creates murky water
and fragments
Physical Control Options
Benthic barriers
Sediment blanket that blocks light, compresses plants
Controls rooted plants
Expensive for large ponds
Requires regular maintenance
Interferes with bottom habitat
Unruly to anchor in large ponds
Drawdown
May be ineffective in wet conditions and without freezing
Increase in some weeds (Potatmogeton, hydrilla)
Physical Control Options
Shading
Aquatic dyes - preemergent,
depths > 2’
Labeled as herbicides
Weed rollers/rakes
www.TheWeedersDigest.com
Mechanical Control Options
Cutting and shredding boats
(“cookie cutters”)
Rotovators – tills sediments
Dredgers – sediment removal
Harvesters – cut & remove
Pros:
Site specific, public perception, use of
harvested biomass
Cons:
Requires opens water surface
& off-site disposal, $$$
Creates fragments
Nonselective, by-catch
Chemical Control Options
Prerequisites for Efficacy
Adequate Concentration
Adequate Contact Time
Appropriate Water Quality
• Turbidity interferes with diquat
Optimal season and
phenological stage
Appropriate chemical for
weed species
• 2,4-d for dicots
EPA registered herbicides for aquatic use
Contact Systemic
Selective Copper
Peroxygen granular (GreenClean®
& Phycomycin®)
2,4-D (Aquaclean/
Navigate)
Triclopyr (Renovate)
Fluridone (Sonar)
Penoxsulam (Galleon)
Bispyribac-sodium (Tradewind)
Broad
spectrum
Endothall, dipotassium salt
(Aquathol)
Diquat (Reward)
Carfentrazone (Stingray)
Flumioxazin (Clipper)
Glyphosate (Rodeo)
Imazapyr (Habitat)
Fluridone (Sonar)
Imazamox (Clearcast)
Mention of tradenames does not indicate endorsement – compounds may be
available from multiple manufactures and under different tradenames
Aquatic Herbicides
Broad spectrum contact herbicides
Endothall (Aquathol K)
• Inhibits respiration & protein synthesis
• Typically non-selective (early season applications can control
over-wintering or early emerging weeds)
• Liquid and pellet formulations allow spot treatment
• Not affected by alkalinity or turbidity
Diquat (Reward, Weedtrine)
• Inhibits photosynthesis & destroys cell membranes
• Binds to suspended sediment – not for use in turbid waters
Both can cause quick kill and potential dissolved oxygen problems
Aquatic Herbicides
Broad spectrum contact herbicides
Carfentrazone (Stingray)
• Use-patterns still being established
• Effective on milfoils & some floating plants (Lemna, Pistia,
Eichhornia, Salvinia) but not others (Landoltia punctata, dotted
duckweed)
• Single applications not effective on plants with high nodal
regeneration capacity (Ludwigia, Hydrocotyle)
• Irrigation restrictions 1-14 days (depending on treatment area)
Flumioxazin (Clipper)
• Watermeal, duckweed, milfoil, hydrilla
Kill by cell membrane disruption (Protox inhibitors – chl biosynthesis)
Quick kill in terrestrial settings, slower with aquatics
Aquatic Herbicides
Selective systemic herbicides
2,4-D (AquaKleen, Navigate)
• Granular formulation contains butoxy-ethyl-ester and should not be
used in water with T&E salmonids
Triclopyr-TEA (Renovate)
• Also commonly used on purple loosestrife
• Liquid and granular
Auxin mimic, plant growth regulator
Selective for dicots (e.g., milfoils, ludwigia, water
chestnut)
Aquatic Herbicides
“Selective” systemic herbicides
Fluridone (Avast, Sonar)
Selective for Eurasian watermilfoil when contact time and
dose can be maintained (long contact time at a low
concentration)
Low toxicity, but requires long contact time (45-80 days),
carotenoid pigment inhibitor
Non-selective at high application rates
Liquid and various pellet formulations
Acts on carotenoid biosynthesis pathway
Aquatic Herbicides
Selective systemic herbicides
Penoxsulam (Galleon)
• Inhibits plant-specific enzyme (acetolactate synthase inhibitor –
branched chain amino acid inhibition)
• Emergent, floating or submersed weed control
• Slow-acting; exposure times for submersed treatments similar to
Fluridone
• Irrigation restrictions: Do NOT apply to water to be used for irrigation
of greenhouse or nursery plants or hydroponics
• Optimum use patterns still being established
Aquatic Herbicides
Broad spectrum systemic herbicides
Glyphosate (Rodeo, AquaMaster)
• Deactivated by sediments
• Not effective on submersed weeds
• Minimal restrictions on irrigation & potable water
• Inhibits amino acid and hormone production by blocking shikimic acid
pathway
Imazapyr (Habitat)
• Inhibits plant-specific enzyme (ALS-inhibitor)
• Slow-acting
• Moderate residual soil activity
Effective for control of floating and emergent weeds with extensive rhizome/root systems
(Phragmites, Typha)
Aquatic Herbicides
Broad spectrum systemic herbicides
Fluridone (Sonar)
• Broad spectrum at high application rates
Imazamox (Clearcast)
• Similar use patterns to Imazapyr (ALS-inhibitor) + some extended
biomass reduction with submersed plants (hydrilla)
• Slow-acting (impacts in 60-120 days)
• Irrigation restrictions vary (still/moving water, depth)
Aquatic Herbicides
Selective Contact Herbicides
• Various copper formulations (copper sulfate & chelated
copper compounds)
• Cu is persistent in the environment
• Peroxygen granular (GreenClean® & Phycomycin®)
• Relatively new algaecides
• Non-copper based (sodium carbonate peroxyhydrate)
Primarily algaecides
Cu is problematic due to effects on salmonid olfaction
Note: These tables are meant only as guidelines. Some herbicides carry specific warnings regarding
toxicity to fish, irrigation water, etc. Please read, understand, and follow all label instructions!
Applications should be made by a certified applicator in accordance with all state and federal regulations.
Source:Whetstone and Heaton. 2013. South Carolina Pest Management Handbook for Field Crops
Note: These tables are meant only as guidelines. Some herbicides carry specific warnings regarding
toxicity to fish, irrigation water, etc. Please read, understand, and follow all label instructions!
Applications should be made by a certified applicator in accordance with all state and federal regulations.
Source:Whetstone and Heaton. 2013. South Carolina Pest Management Handbook for Field Crops
Things to consider
• The label!
• Perceptions / community
• Movement of propagules
• Implications of no treatment
• Herbicide resistance
• NPDES requirements addressed by OR DEQ’s:
• Pesticide General Permit (2300-A): discharge in,
over or near surface water
• General Permit for Pesticide Use in Irrigation
Systems (2000-J)
Dreissenid Mussels
Dreissena polymorpha (zebra mussel) D. rostriformis bugensis (quagga mussel)
Small, epifaunal, freshwater bivalves
Dreissenid Mussles
Rapid growth (15-20 mm/yr)
Prolific reproducers (40K – 1 M eggs/yr)
Form dense colonies (200,000+/m2)
$0.5 Billion impact if introduced in Columbia Basin
Dreissenid Mussels
Watercraft Inspection Stations
Set up for mussels but find more aquatic weeds than anything else
Crayfish • Signal native to OR and WA
• Invaders can impact benthic community, macrophyte abundance, and aquatic foodwebs
Ringed Rusty Red Swamp Signal Northern
Orcon- Orcon- Procamb- Pacifast- Orconectes
ectes ectes arus acus virilis
neglectus rusticus clarkii leniusculus
Potamopyrgus antipodarum New Zealand Mudsnail
• Small (<5 mm) primarily freshwater snail
• Herbivorous scrapers, grazers
• Can develop very high densities (400k/m2 in Columbia R)
• Density-dependent impacts
– Consume primary production/compete with native gastropods, grazers, and detritivors
• Management
– Prevention
– Gear cleaning
Photo by D.L. Gustafson
