Chemical Control of Aquatic Weeds - MidSouth Aquatic Plant

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Chemical Control of Aquatic Weeds Ryan M. Wersal, PhD Lonza Microbial Control, Alpharetta Innovation and Technology Center

Benefits of Aquatic Plants • Stabilize lake sediments, reduce resuspension • Increase sedimentation, reduce turbidity • Provide habitat for insects, forage fish, fish spawning and YOY fish

• Provide food for waterfowl, other animals

Native Vs. Non-native

Plant Species Designation • Aquatic plant species can be designated as: – – – – – –

Native Non-native Invasive Native Invasive Non-native Invasive And Others (i.e. Non-native Naturalized)

• This often creates confusion with the public and resource managers • As well as determining management strategies – Including herbicide selection

Goal of Management • Remove nonindigenous plants and restore a diverse community of desirable native plant species

Pretreatment

4 WAT

12 WAT Pond near Starkville, MS 70% coverage by waterhyacinth

What Do Herbicides Do? • Controlled/selective plant poisoning – applied to soil (root uptake), water, and/or leaves (foliar uptake) – contact or systemic – selective vs. non-selective

How Herbicides Work • Mode/mechanism of action, where a specific plant process is targeted – – – – –

photosynthesis pigments enzymes growth hormonal balance

DQ

DQH2

O2 -

Advantages of Herbicide Use • Cost effective • Predictable, consistent efficacy

• Relative ease of application • Minimal ecosystems impacts

Advantages of Herbicide Use • Can treat small as well as large areas • Proper choice, rate, timing = selectivity • Newer Products – excellent toxicology profiles • Compatible with other management options

• Best tool for initially removing large amounts of nuisiance vegetation

Disadvantages of Herbicide Use • Commitment to long-term management • Use restrictions

– When/where you can apply – Drinking, swimming, fishing, irrigation, livestock

• Can sometimes select for a worse problem

• Target plants can recover • Public perception of chemical use – Human/eco-toxicology issues – Fear of pesticides

Misconceptions with Aquatic Herbicides • Aquatic plants “take up” most of the herbicide – Plant uptake = 1 to 5% of herbicide

• Herbicides mix rapidly top to bottom – Herbicide trapped via thermal gradients

• Dispersion is a minor factor – All 3 ppm treatments should work the same – Wind/Flow move herbicide off-target

• Herbicides Are Dumped Into the Water

Potential Environmental Concerns • Potable Water • Lowered dissolved oxygen (DO) and warm water – Whole vs. Partial treatment – Fish mortality may result

• Nutrients released

– Increased turbidity (algal bloom)

• Crop/landscape damage due to irrigation (MS Delta alligatorweed and soybeans) – Choice of herbicide • 1/2 life, sensitivity of non-target plants – Posting requirements – Time, Setback Distance, Herbicide Concentration

13 Herbicides Registered for Aquatic Use • Section 3 herbicides • All products have terrestrial uses

– Glyphosate and 2,4-D - major use on food crops

• Glyphosate and Imazapyr - Emergent • Copper, Endothall, Fluridone - Submersed • Diquat, 2,4-D, Triclopyr, Carfentrazone, Imazamox, Penoxsulam, Flumioxazin, and Bispyribac-sodium – Emergent and submersed uses

Aquatic Herbicide Mode of Action 2,4-D

Auxin mimic / plant growth regulation

Bispyribac-sodium

Plant enzyme inhibition / ALS

Carfentrazone-ethyl

Inhibits PPO enzyme / chlorophyll

Copper

Inhibits photosynthesis

Diquat

Inhibits photosynthesis

Endothall

Respiration / photosynthesis inhibition

Flumioxazin

Inhibits PPO enzyme / chlorophyll

Fluridone

Pigment synthesis

Glyphosate

Plant enzyme inhibition / EPSPS

Imazamox

Plant enzyme inhibition / ALS

Imazapyr

Plant enzyme inhibition / ALS

Penoxsulam

Plant enzyme inhibition / ALS

Triclopyr

Auxin mimic / plant growth regulation

Herbicide Translocation and Selectivity Herbicide

Translocation

Selectivity

2,4-D

Systemic

Selective

Bispyribac-sodium

Systemic

Broad spectrum

Carfentrazone-ethyl

Contact

Selective

Copper

Contact

Broad spectrum

Diquat

Contact

Broad spectrum

Endothall

Contact

Selective (Timing)

Flumioxazin

Contact

Broad spectrum

Fluridone

Systemic

Selective (Rate)

Glyphosate

Systemic

Broad spectrum

Imazamox

Systemic

Selective

Imazapyr

Systemic

Broad spectrum

Penoxsulam

Systemic

Selective (Rate)

Triclopyr

Systemic

Selective

Herbicide Degradation & Half-life Herbicide

Degradation

½-life in water (days)

2,4-D

Microbial, Photolysis

7 to 48

Bispyribac-sodium

Microbial

Carfentrazone-ethyl

Hydrolysis, Photolysis

3 to 8 (pH dependent)

Copper

Chemically bound

Hardness dependent

Diquat

Adsorption, Photolysis

1 to 7

Endothall

Microbial

4 to 7

Flumioxazin

Photolysis, Microbial

3-5 d (pH 5) to 14-22 min (pH 9)

Fluridone

Photolysis, Microbial

20+

Glyphosate

Adsorption, Microbial

14

Imazamox

Microbial, Photolysis

7 to 14

Imazapyr

Photolysis, Microbial

2 to 4

Penoxsulam

Photolysis, Microbial

15+

Triclopyr

Photolysis, Microbial

0.5 to 3

~ 30

Aquatic Herbicide Toxicity Typical Rates in H2O (ppm)

Bluegill 96-hr LC-50 (ppm)

0.5 to 4.0

168

Bispyribac-sodium

0.015 to 0.045

> 100

Carfentrazone-ethyl

0.2

>5000

Copper

0.2 to 1.0

Soft water: 0.88, Hard water: 7.3

Diquat

0.1 to 0.37

245

Endothall

0.3 to 3.0

Dipotassium salt: 343, Alkylamine salt: 0.94

Flumioxazin

0.1 to 0.4

>21

0.005 to 0.03

891

Glyphosate

NA

>1000

Imazamox

0.05 to 0.075

>100

Imazapyr

NA

>100

Penoxsulam

0.01 to 0.04

103

Triclopyr

0.75 to 2.5

891

Herbicide 2,4-D

Fluridone

Copper (1950’s) • Target weeds: hydrilla, planktonic algae, filamentous algae, chara/nitella, coontail, milfoil spp., pondweed spp. • Subsurface application

• Typical use rates: 0.5 to 1 ppm • Max concentration: 1 ppm

• Restrictions

– Label changes are coming for copper products

Due to multiple manufacturers, follow all label instructions regarding rate, adjuvants, application technique, and use restrictions. Check with appropriate regulatory agencies before purchasing or applying pesticides to the water. Always Follow The Label!

2,4-D (1959)

• Target weeds: Eurasian watermilfoil, water hyacinth, coontail, waterlily, parrotfeather

• Subsurface and foliar application • Typical use rates: 0.5 to 4 ppm, 2 to 4 lb ae/A

• Max concentration and rate: 4 ppm, 4 lb ae/A • Restrictions – – – – – –

Potable water intake: 5 to 14 days (1 to 4 ppm) Drinking water setback: 600 to 2400 ft (1 to 4 ppm) Swimming (butoxyethanol ester only): 24 hr Drinking: concentration
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Chemical Control of Aquatic Weeds - MidSouth Aquatic Plant

Chemical Control of Aquatic Weeds Ryan M. Wersal, PhD Lonza Microbial Control, Alpharetta Innovation and Technology Center Benefits of Aquatic Plant...

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