Everything You Wanted to Know About Granules but Were Afraid to

Ask

Brett W. Bultemeier & W. T. Haller

University of Florida, IFASCenter for Aquatic and Invasive Plants

http://plants.ifas.ufl.edu

Introduction

• Granules have been used to control aquatic plants for many years

• Granule = formulation of herbicide where a solid carrier is utilized– Clay pellet, granule, polymer etc…

Current list of aquatic granules• Copper

• Endothall

• Triclopyr

• 2,4-D

• Fluridone – Quick to slow release

Introduction• Research focus has been on liquids

– How it dilutes and breaks down– Granule similar to a liquid after herbicide released

• Regardless of formulation it is the contact exposure time that matters

– How long at what concentration to control plants (Contact Exposure Time - CET)

endothall= short exposure (hrs) high rates (ppm)fluridone= long exposure (days) low rates (ppb)

Milfoil - endothall (Netherland JAPM 1991)

Justifications for use

• Granule will sink below the thermocline

Thermocline

Justifications for use

• Granule will sink below the thermocline

• More precise placement?

• Allows an extended release of herbicide?

Placement

Growing points

•Use less herbicide by targeting treatment?

•Keeps herbicide on site, less drift?

•Concentrate herbicide on the bottom?

Extended Release of Herbicide?

• Allows extended release without retreatment

• In flowing water prevents rapid loss of herbicide

Time (days)0 10 20 30 40 50

Her

bici

de C

once

ntra

tion

(ppb

)

0

5

10

15

20LiquidGranular

Previous Work on Granules

• Little work has been done because

Complicated

Why Complicated• Rate of release

– Granule: type, carrier, integrity– Herbicide: solubility, adsorption to granule– Water: temperature, flow, pH, chemistry

• Soil– Sediment hardness, organic matter, clay content

• Herbicide plant interactions– Root absorbed???– Translocate???– Contact Exposure Time - CET

Questions

• What is the release rate of granules

• What does water movement do to release

• Sediment impact on release

• Herbicide uptake by plant

Testing Granular Release• Evaluate the release rate of herbicide from

granules (create a release curve)

• Static and gently aerated tested

• 5 gal plastic pails

• Sample over time– Up to 90 d for some

• Maintained in dark at 20°C

Time (days)

0 10 20 30 40 50 60 70 80 90 100 110 120

Per

cent

Rel

ease

of h

erbi

cide

from

Gra

nule

"A"

0

10

20

30

40

50

60

70

80

90

100

110 y= 70.4 (1-e-0.02x), r2= 0.89

Static

ET50= 61 d

Time (days)

0 10 20 30 40 50 60 70 80 90 100 110 120

Per

cent

rele

ase

of h

erbi

cide

from

Gra

nule

"A"

0

10

20

30

40

50

60

70

80

90

100

110 y= 114.3 (1-e-0.10x), r2= 0.87

Aerated

ET50= 6 d

Time (days)

0 2 4 6 8 10 12 14

Perc

ent o

f rel

ease

from

Gra

nule

"X"

0

10

20

30

40

50

60

70

80

90

100

110

y= 113.7 (1-e-1.17x), r2= 0.95

Static

ET50= 12 h

Time (days)

0 2 4 6 8 10 12 14

Per

cent

of r

elea

se fr

om G

ranu

le "X

"

0

10

20

30

40

50

60

70

80

90

100

110 y= 103.6 (1-e-14.14x), r2= 0.83

Aerated

ET50= 1.2 h

Impact of Water Movement

• 10 x difference between static and aerated samples– Water movement speeds up release??– Not enough movement to disturb granule

piles- i.e. not aggitated• Boundary layer?

10% Granule= 100,000 ppm; solubility= 10 ppmZone a= 10 ppmZone b= 9 ppmZone c= 6 ppmZone d= 1 ppm

Further Questions• Sediment granule interaction

– Does the granule sink in to sediment– Does soil binding occur– What changes occur to the rate of release

• Plant uptake

– Do roots absorb herbicide– Does the herbicide translocate

Why does all this mater?• Granules have been used for years, they must

work– Have they always been utilized as efficiently as

possible

• Why does it matter how long it takes?– Hard to predict a CET if release is unknown

Efficient and cost effective treatments are the goal so you need to know how

products work to achieve that goal

Questions?

plants.ifas.ufl.edu

Thank You