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 Academic
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Certificate
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Classes
by Phil Busey
Degree
Requirements
Golf
and Sports Turf
Grass
Biology
Landscape
IPM
Living
Lawn
Turfgrass
Culture
Research
Interests
Weed
Science
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Weed
Science
Broadleaf
Weed Control Reseach Update
Since the following research summary was written
in 2002, the sulfonylurea herbicide Certainty®
has shown very good results in controlling dollarweed, and there
have been changes in the labeling of several products. Lontrel is
no longer available for landscape use, and the SpeedZone products
have had major changes in their labels so they are no longer available
for use in Floratam St. Augustinegrass in Florida.
Since the 1950s, atrazine has been the standard
postemergence herbicide for broadleaf weed control in St. Augustinegrass
turf. More recently, four new broadleaf herbicides have been
labeled for the same purpose: Lontrel® (1999, Dow AgroSciences);
Manor™ (2000, Riverdale Chemical Company); SpeedZone™
St. Augustine Formula (2001, PBI Gordon Corporation); and
Blade™
(2002, PBI Gordon Corporation).
Unlike atrazine which is generally harmful to other grasses, Blade™,
Lontrel®, Manor™,
and SpeedZone™ St. Augustine Formula are also labeled for certain
other warm-season turfgrasses. The purpose of this web page
is to provide a brief update on the relative weed control usefulness
of all four products, and pertinent history.
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| Damage
to cultivars of St. Augustinegrass from summer application of
atrazine on a sod farm. Bitterblue and other cultivars
are severely injured at rates that do not visibly affect Floratam. |
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The observations
on which weed control usefulness is based are replicated experimental
plots that I established and evaluated from 1999-2002 in Broward
County and Palm Beach County, Florida. The data demonstrate
relative efficacy of control of selected subtropical weeds, and
phytotoxicity to St. Augustinegrass turf, both in lawn areas and
sod. This is not meant to be comprehensive of all the weeds
controlled by these products, nor is it meant to represent weed
control usefulness outside the experimental area of subtropical
South Florida. The herbicides are also labeled for use on
other subtropical turfgrasses, but this report focuses on St. Augustinegrass,
the main turf of Florida. First, some history.
Atrazine
Atrazine
was adopted in the 1950s as the main postemergence herbicide for
broadleaf weed control in St. Augustinegrass, after sod producers
observed damage from phenoxy herbicides containing 2,4-D.
After consulting with Dr. Evert O. Burt, weed scientist at the University
of Florida, Ralph W. White (Agricultural Extension Turf Specialist
at the University of Florida) tested low rates of triazine herbicides
for the control of broadleaf and grassy weeds. It was discovered
from research that White did in Davie, Florida, that simazine and
atrazine were effective for selective weed control in St. Augustinegrass.
This was a major breakthrough for growers to produce clean sod for
the consumers. Atrazine can also be used on centipedegrass.
Unlike the other herbicides discussed here, atrazine has considerable
preemergence weed control activity. The Floratam cultivar
of St. Augustinegrass is so resistant to atrazine that, after its
release in 1973, Floratam became the main turfgrass grown for sod
in Florida. Weeds are always a major problem in turfgrass
production, but this was most clear when growers expanded their
acreage in the rich humus soils of the Everglades Agricultural Areas.
Something unusual about atrazine and St. Augustinegrass is that
most turfgrasses are injured by atrazine, and cool-season turfgrasses
are severely damaged at even low rates of atrazine, so St. Augustinegrass
is fairly unique.
Unfortunately,
there are drawbacks to atrazine. It is relatively highly water
soluble, therefore in some parts of the United States, such as the
Midwest, atrazine has been discovered in groundwater. Secondly,
not all St. Augustinegrasses are equally tolerant of atrazine, and
summer applications can be destructive. Bitterblue and FX-10
St. Augustinegrasses have less tolerance for atrazine than does
the Floratam cultivar of St. Augustinegrass. Manufacturers
have elected to label professional liquid formulations of atrazine
as a Restricted Use Pesticide, so that only licensed users may apply
those formulations, with the stipulation that they may not be applied
after tax day, April 15th, until October 1st, although different
labels describe this differently. (Surprisingly, homeowners
can purchase both granular weed-and-feed mixtures as well as certain
liquid atrazine formulations, and do not have strict prohibition
from April 16 through September 30th). The third problem
with atrazine is that pest control operators have reported inconsistent
results from using it to control certain important broadleaf weeds,
such as dollarweed. Dollarweed is the most common broadleaf
weed in St. Augustinegrass in Florida, in part because of the excessive
irrigation used by homeowners, and the fact that dollarweed
is a water-loving plant.
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Time-course
of weed control by several broadleaf postemergence herbicides
applied to control dollarweed, Hydrocotyle umbellata (pennywort).
Manor™
and Blade™
are identical in active ingredient and concentration, but
they differ in packaging. The container of Blade™ contains
a measuring cylinder with attached funnel that it appears
would be effective in measuring the small quantities used.
Trimec
Southern is not labeled for use on St. Augustinegrass.
Not shown are additional mixtures such as Manor+Lontrel, which
was slightly more effective than Manor or Lontrel, and a three-way
mixture of 2,4-D, dicamba, and mecoprop, which was less effective
than the same mixture with carfentrazone-ethyl. Plots
were treated on 25 January 2002, wind speed was less than
5 miles per hour. The day was sunny and the high temperature
was 85.5 F (29.7 C)
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Lontrel®
Each
of the "new" broadleaf herbicides has some history.
Lontrel® contains the active ingredient clopyralid, which appeared
previously in the turf product Confront, a right-of-way material
which also contains triclopyr. Lontrel® has excellent
turf safety, and is particularly effective against several families
of weeds, especially the Asteraceae or sunflower family including
groundsels; but also the Fabaceae, or pea family including the clovers;
the Polygonaceae, or knotweed family; and the Solanaceae, or nightshade
family. In Florida, California, and New York, the maximum
use rate is 2/3 pint per acre per growing season, which is only
one-half of the suggested application rate for some difficult weeds.
Some applicators have gotten improved results by mixing Lontrel®
with other herbicides, but one must be cautious to carefully test
new mixtures in small areas.
Manor™
and Blade™
Manor™
and Blade™ have the active ingredient metsulfuron, which was
used previously in the herbicide DMC marketed by O. M. Scotts and
Sons briefly in the 1990s. Metsulfuron has been the active
ingredient of the agricultural herbicide Escort, also labeled for
unimproved turf, and which in July 1997 received a 24C Special Local
Needs label for St. Augustinegrass sod in Florida. Although
I wrote a letter in support of the 24C label, most of the credit
goes to Dr. Bert McCarty of Clemson University, based on research
that he had done while with the University of Florida. Manor™
and Blade™ are very slow acting, but are effective against
some particularly difficult weeds such as alligatorweed, a problem
in some South Florida sod farms. Manor™ and Blade™
are effective at 0.25 to 1.0 ounces per acre, although 0.50 ounces
per acre is commonly used. Manor™ and Blade™
may not be used on bahiagrass, except to control it as a weed.
Because such small rates of application of Manor™ and Blade™
are effective, extreme precautions must be taken to accurately weigh
the small amounts needed. This may require an analytical balance.
The packaging of Blade™ contains a built-in measuring cylinder that
appears would be effective in measuring the small quantities used.
(The other broadleaf herbicides discussed here are liquids.)
SpeedZone
St. Augustine™ Formula
SpeedZone™
St. Augustine Formula contains the new turf herbicide carfentrazone-ethyl,
which the EPA considers a Reduced Risk Pesticide, effective in herbicide
mixtures at rates as low as 0.02 pounds per acre. Because
of this, the EPA fast-tracked the approval process. PBI Gordon
obtained the exclusive U.S. non-agricultural marketing rights to
carfentrazone-ethyl in combinations from FMC Corporation.
In mixtures such as SpeedZone™ St. Augustine Formula, carfentrazone-ethyl
quickly kills difficult broadleaf weeds such as clover, spurge,
Old World diamondflower, and alligatorweed. Weed foliar injury
is often noticed within hours after application, and most of the
weed control is accomplished within 4 days, based on my experience.
Carfentrazone
is in the triazolinone family which is believed to disrupt cell
membranes similar to the diphenyl ethers by inhibiting the enzyme
protoporphyrinogen oxidase (the PROTOX enzyme), thus they are called
PPO-inhibiting. This activity leads to peroxidation due to
accumulation of a singlet oxygen in the presence of light, and death
of contacted leaf areas upon
exposure to light. Other PPO-inhibitors include oxyfluorfen
and oxadiazon.
SpeedZone™
St. Augustine Formula is also unusual in containing the herbicide
2,4-D which was generally thought to be damaging to St. Augustinegrass. In
the mid 1980s Dr. Wayne Currey, then turfgrass weed scientist for
the University of Florida, observed considerable difference in the
St. Augustinegrass injury among different phenoxy herbicide products. The
differences were due to the concentration of herbicides other than
2,4-D, particularly mecoprop (once called MCPP), in the mixtures. From
many experiments that I have performed in South Florida, mecoprop
and not 2,4-D appears to be the killer of St. Augustinegrass.
SpeedZone™ St. Augustine Formula contains a reduced concentration
of mecoprop, and I have not seen injury to St. Augustinegrass from
labeled rates applied at any season of the year.
The fourth
component of SpeedZone™ St. Augustine Formula is dicamba, another
common component of phenoxy herbicides for turf, and it helps boost
the control of perennial broadleaf weeds. The 2,4-D is in
an ester, and because of this there is less odor, but more potential
from volatile movement into the air, though as the isooctyl ester
it has less volatility than other esters. Use rate is 2-4
pints per acre in St. Augustinegrass.
Methods
Dollarweed
areas were chosen at the Fort Lauderdale Research and Education
Center, based on nearly solid coverage. There was a thin understory
of bermudagrass. Plots 4 ft X 8 ft (122 cm X 244) cm were
assigned to six replicates based on condition. Herbicide treatments
were applied with a CO2-pressurized backpack sprayer calibrated
to deliver 22.6 gallons per acre (678 L/ha) at 30 psi (207 kPa)
with 11002 flat-fan nozzles. The herbicide treatments were
Atrazine 4L (2 pt/A), a low rate; Lontrel® (3/4 pt/A); Manor™
(0.5 oz./1000 ft2); SpeedZone™ St. Augustine Formula (3 pt/A);
Trimec Southern (1.5 pt/A); water control, and two mixtures (not
shown in the graph above) Lontrel®+Manor™;
and 2,4-D+mecoprop+dicamba. Plots were evaluated visually
for dollarweed injury each day for 10 days, and twice per week thereafter.
Results
Within
3 weeks, atrazine, SpeedZone™ St. Augustine Formula, and Trimec
Southern (not labeled for St. Augustinegrass) were equally effective
in controlling dollarweed, averaging about 90% control. SpeedZone™
St. Augustine Formula was faster than atrazine and Trimec Southern,
reaching a plateau of weed control by 5 days after treatment.
Manor™ caused slow kill of dollarweed, but at 21 days had achieved
only about 60% control. Lontrel® was not effective, and
caused only 25% injury to dollarweed. These results were similar
to others obtained in other experiments, including more difficult
weeds such as Old World diamondflower and alligatorweed.
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