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
