Florida Cooperative Extension Service
Weed Management for Florida Golf Courses1
L. B. McCarty2
A weed can be defined as any plant out of place
or growing where it is not wanted. For example,
bahiagrass is considered a weed when grown in a pure
stand of bermudagrass but is highly desirable when
grown in a monoculture such as a golf course rough.
In addition to being unsightly, weeds compete with
turfgrasses for light, soil nutrients, soil moisture, and
physical space. Weeds also are hosts for pests such as
plant pathogens, nematodes, and insects. Certain
weeds are irritants to humans when allergic reactions
to pollen or chemicals occur.
The most undesirable characteristic of weeds in
turf situations is the disruption of visual turf
uniformity. This happens when different (a) leaf
width or shape, (b) growth habit, or (c) colors are
present. Many broadleaf weeds such as dandelion,
plantains, and pennywort have a wider leaf than the
dominant turf species. They also have different leaf
shapes. The growth habit of smutgrass, goosegrass,
vaseygrass, and thin paspalum, results in clumps or
patches that also disrupt turf uniformity. In addition,
large clumps are difficult to mow effectively and
increase maintenance problems. The lighter green
color typically associated with certain weeds such as
annual bluegrass in a golf green often distracts from
the playing surface.
WEED OCCURRENCE IN TURF
Weed control for turf managers can be a difficult
chore due to several reasons. Florida, unlike most
parts of the country, has a very mild climate with few
deep freezes. As a result, many traditional annual
weeds behave as semi-annuals or even perennials.
For example, year-round weed pressure can occur in
Florida from annuals such as crabgrass and
goosegrass, but in most parts of the country where
frost occurs, these die out yearly. Florida's mild
climate also allows the growth of many sub-tropical
and tropical weeds that do not occur in any other
location in the country. As a result, little research has
been performed on their susceptibility to most
Much of Florida's soils also consist of sands. As
a result, many herbicides are not retained in the
upper soil profile as well as in heavier soil and this
reduces their effectiveness time. The effectiveness
times of herbicides are further shortened due to
Florida's year-round mild weather and adequate
amounts of rainfall. These conditions encourage
quicker breakdown by soil microorganisms.
Florida's mild climate also encourages other year-
round pest problems which injure and weaken the
turf stand. These weakened or bare turf areas allow
1. This document is Circular 1114, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida.
Publication date: July 1993.
2. L. B. McCarty, Associate Professor, Environmental Horticulture Department; Cooperative Extension Service, Institute of Food and Agricultural
Sciences, University of Florida, Gainesville FL 32611.
The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research,
educational information and other services only to individuals and institutions that function without-regard to race, color, sex, age, handicap,
or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension Service office.
Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / John T. Woeste, Dean
Weed Management for Florida Golf Courses
establishment of weeds. In addition, St.
Augustinegrass and bahiagrass, the most widely used
turf species in the state, have relatively poor tolerance
to most postemergence herbicides. As a result, weed
control becomes a challenge for most turf managers
in the state.
Weeds often are the result of a weakened turf,
not the cause of it. Understanding this helps to
explain the major reason for weed encroachment into
a turf area (e.g., thin turf density and bare spots).
Reasons for weak or bare turf areas are numerous.
These include: (a) improper turf species selection not
adapted to environmental conditions; (b) damage
from turfgrass pests such as diseases, insects,
nematodes and animals; (c) environmental stresses
such as excessive shade, drought, heat and cold; (d)
improper turf management practices such as misuse
of fertilizer and chemicals, improper mowing height
or improper mowing frequency and improper soil
aeration; and (e) physical damage and compaction
from concentrated or constant traffic. Unless factors
which contribute to the decline of a turf area are
corrected, continued problems with weed
establishment should be expected.
FORMULATING A WEED
Weed control is an integrated process where good
cultural practices are employed to encourage desirable
turfgrass ground cover as well as the intelligent
selection and use of herbicides. A successful weed
management approach involves the following:
1. Proper weed identification
2. Prevention of weed introduction
3. Providing proper turfgrass management or
4. If necessary, the proper selection and use of
The first step to proper weed management and
control is proper identification. Turf managers should
be able to identify each weed to genus and preferably
to species to select the appropriate control technique.
Weed identification also is the first step in
understanding why weeds occur and how to control
them. For instance, most sedges prefer moist, wet
areas while sandspur prefer drier sites.
Identification begins with classifying the weed
type. Broadleaves, or dicotyledonous plant, have two
seed cotyledons (young leaves) at emergence and
have net-like veins in their true leaves. Broadleaves
often also have colorful flowers. Examples include
clover, spurges, lespedeza, plantain, henbit, pusley,
beggarweed, and matchweed, among others. Grasses,
or monocotyledonous plants, only have one seed
cotyledon present when a seedling emerges from the
soil. Grasses also have hollow, rounded stems with
nodes (joints), and parallel veins in their true leaves.
Examples include crabgrass, goosegrass, dallisgrass,
thin (bull) paspalum and annual bluegrass. Sedges
and rushes generally favor a moist habitat and have
either stems which are triangular-shaped and solid
(sedges), or round and solid (rushes).
Weeds complete their life cycles in either one
growing season (annuals), two growing seasons
(biennials) or three or more years (perennials).
Annuals that complete their life cycles from spring to
fall are generally referred to as summer annuals, and
those that complete their life cycles from fall to spring
are winter annuals. Summer annual grasses, as a
class, are generally the most troublesome in turf.
In the past, proper weed identification was
difficult to achieve due to the lack of a suitable guide.
Most guides pictured weeds in unmowed conditions
or did not list all the important turf weeds. Recently,
a publication jointly produced by The University of
Florida, Georgia and Auburn University has become
available which covers most major weeds in the
southern United States. Weeds of Southern
Turfgrasses provides color photographs of 193 major
weeds with detailed descriptions, life cycles, and
world-wide distribution information. Most of the
photographs were taken of mowed turf. This guide is
available at the following address:
Weeds of Southern Turfgrass ."
P. O. Box 110011
University of Florida
Gainesville, FL 32611-0011
The cost of the publication is $8.00 per copy plus 6%
sales tax for Florida residents. Checks should be
made payable to the University of Florida. 101
Weed Management for Florida Golf Courses
Weed prevention means avoiding the introduction
of weeds into an area. There are national, state and
local prevention efforts against the introduction and
spread of weeds. A local preventive program is one
of the best methods of avoiding future weed
problems. Many of these methods are commonsense
approaches that ensure sanitary conditions and
minimize weed introduction. Some of these methods
include use of weed-free turf seeds, stolons, sprigs,
plugs or sod. Washing between mowings, maintaining
weed-free fence lines and ditch banks and the use of
clean mulch and topdressing material are additional
examples of preventive methods.
Cultural practices promoting a vigorous, dense
turf, are perhaps the most important and least
recognized means of preventing weed encroachment
and establishment. Soil fertility, aeration, and
moisture levels should be maintained at an optimum
level to promote turf cover. Since light is required
for the germination of weeds such as crabgrass and
goosegrass, cultural practices increasing turf density
will prevent light from reaching the soil surface.
Blocking light from the soil surface also delays
germination in the spring of weed seeds that require
warmth, because the soil surface is better insulated,
thus it remains cooler. Maintaining the highest
cutting height possible and adequate fertility levels
will- help encourage a high shoot density and will
minimize light penetration into the soil surface.
Heavy pressure of particular weeds might also
indicate specific soil conditions which favor the weed
occurrence. Table 1 lists some of these soil
conditions and associated weeds. Continued weed
problems can be expected until these growth
conditions are corrected.
Herbicides may be classified according to
chemistry, method of application, timing of
application, persistence, selectivity, and mode of
Selective. A selective herbicide controls or
suppresses certain plant species without seriously
affecting the growth of another plant species.
Table 1. Weeds as
indicators of specific poor soil
Soil Condition Indicator Weed(s)
Low pH Sorrel
Soil compaction Goosegrass, knotweed, Poa
Low nitrogen levels Legumes (clover, chickweed)
Poor (sandy) soils Poorjoe, sandspur, quackgrass
Poor drainage Sedges
Surface moisture Algae
High pH Plantains
High nematodes Spurges, pusley, knotweed
Low mowing Algae
Selectivity may be due to differential absorption,
translocation, morphological and/or physiological
differences between turfgrasses and weeds. The
majority of herbicides used in turfgrasses are selective
in nature. For example, 2,4-D is used for selective
control of many broadleaf weeds, such as spurge,
without significant injury to turfgrasses.
Nonselective. Nonselective herbicides control
plants regardless of species. These are generally used
to control all plants as in the renovation or
establishment of a new turf area, "spot treatments" or
a trimming material along sidewalks. Glyphosate and
diquat are examples of nonselective herbicides.
Herbicides such as atrazine or MSMA can be
nonselective at rates in excess of those used for
Systemic. Systemic herbicides are extensively
translocated (moved) in the plant's vascular system.
The vascular system translocates the nutrients, water
and organic materials necessary for normal growth
and development. In contrast to the quick kill
observed with contact herbicides, systemic herbicides
require several days or even a few weeks to be fully
translocated throughout the plant's vascular system,
and therefore, require a longer time before kill.
Systemic herbicides are also classified as selective or
nonselective. Glyphosate is a nonselective, systemic
herbicide while 2,4-D, dicamba (Banvel), imazaquin
(Image), and sethoxydim (Vantage) are examples of
selective, systemic herbicides.
Weed Management for Florida Golf Courses
Contact. Contact herbicides only affect the
portion of green plant tissue contacted by the
herbicide spray. These herbicides are not, or are only
to a limited extent, translocated in the vascular system
of plants. Therefore, underground plant parts such as
rhizomes or tubers are not killed. Usually repeat
applications are needed with contact herbicides to kill
regrowth from these underground plant parts.
Adequate spray volumes and thorough coverage of
the weed foliage are necessary for effective control.
These herbicides kill plants quickly, often within a few
hours of application. Contact herbicides may be
classified as selective or nonselective. Bromoxynil
(Buctril) and bentazon (Basagran T&O) are classified
as selective, contact herbicides. Diquat is a
nonselective, contact herbicide.
Herbicides from the same class of chemistry are
grouped into families in much the same way plants
are grouped into genus and species. In general,
members of a herbicide family are similarly absorbed
and translocated and have similar mode of actions.
TIMING OF HERBICIDE APPLICATION
Herbicides are also classified by when the
chemical is applied in respect to turfgrass and/or weed
seed germination. Although the majority of
herbicides may be classified into one category,
atrazine (AAtrex), simazine (Princep), dithiopyr
(Dimension), and pronamide (Kerb) are exceptions.
They are used as both preemergence and
Preplant herbicides. These are applied before
turfgrass is established, usually to provide
nonselective, complete control of all present weeds.
Soil fumigants, such as metam-sodium or methyl
bromide, and nonselective herbicides such as
glyphosate (Roundup) may be used as nonselective
Preemergence herbicides. Preemergence
herbicides are applied to the turfgrass site prior to
weed seed germination and form a barrier at, or right
below, the soil surface. This group of herbicides
prevents cell division during weed-seed germination as
the emerging seedling contacts the herbicide layer
(Figure 1). Weeds that already have emerged
(visible) at the time of application are not controlled
consistently by preemergence herbicides since their
primary growing points escape treatment.
Figure 1. Preemergence herbicides form a barrier at or just
below the soil surface and are relatively ineffective on
Postemergence herbicides. Postemergence
herbicides are applied directly to emerged weeds. In
contrast to preemergence herbicides, this group of
herbicides provides little, if any, soil residual control
of weeds. A complete chemical weed control
program can be accomplished with postemergence
herbicides, provided multiple applications are used
throughout the year. However, due to the necessity
of repeat applications and temporary turfgrass injury,
most turfgrass managers use postemergence
herbicides in conjunction with a preemergence weed
control program. Postemergence herbicides are
useful to control perennial grasses and broadleaf
weeds that are not controlled by preemergence
herbicides. Certain postemergence herbicides may
also be used on newly established turfgrasses.
SOIL FUMIGATION FOR NONSELECTIVE
PREPLANT WEED CONTROL
Soil fumigants are volatile liquids or gases that
control a wide range of soil-borne pests. Soil
fumigants are also highly toxic and are expensive.
Their use is limited to small, high cash crop acres
such as tobacco, certain vegetables, fruits, bedding
plants and turf. The expense usually occurs because
of a cover necessary to trap the fumigant vapors in
the soil. Fumigants control not only most weed
species, but also many nematodes, fungi and insects.
Weed species that have a hard, water-impermeable
seed coat such as sicklepod, white clover, redstem
Weed Management for Florida Golf Courses
filaree, and morningglory are not effectively
controlled with soil fumigants. Important
considerations before choosing a particular soil
fumigant include expense, soil moisture level, soil
temperature, and time available before planting.
Several compounds are or have been used as
fumigants. The two most used materials in turf are
methyl bromide and metham or metam-sodium.
Methyl bromide. Methyl bromide is a colorless,
*nearly odorless liquid or gas. At 380F, the liquid
turns into a gas and at 680F is 3.2 times heavier than
air. These properties require a cover to be used with
methyl bromide or the material will escape. Methyl
bromide is extremely toxic (acute vapor toxicity is 200
ppm) due to a serious inhalation hazard and it is
commonly combined with a warning agent such as
chloropicrin teargass) to warn the user of escapage.
When using this fumigant, the soil should be in a
condition suitable for planting, including seedbed
preparation by proper tilling. Normally, control is
achieved only as deep as the soil is properly tilled.
Soil should be moist for adequate soil fumigant
penetration and dispersion. Saturated or extremely
dry soils limit penetration and dispersion and
subsequently affect weed seed absorption. Soil
temperatures at four inches should be a minimum of
60F. Fumigation is not effective if soil temperatures
are below 500F. Prior to or during application, the
plastic or polyethylene cover should be placed with
ends properly secured to .prevent gas leakage. The
treated area should be covered for 24 to 48 hours.
The cover should then be removed and the soil
aerated for 24 to 72 hours before planting.
Metham or metam-sodium. Metham (sodium
methyl-dithiocarbamate) is a member of the
thiocarbamate herbicide family. Metham is water-
soluble, and upon contact with moist soil it breaks
down to form the highly toxic and volatile chemical
methyl isothiocyanate. Like methyl bromide, metham
should be applied to moist soils with temperatures of
at least 600F. It is most effective when its vapors are
confined with a cover; however, a water and soil-seal
method may be used without a cover. With the water
and soil-seal method, the soil is cultivated and kept
moist for a week before treatment. The material is
applied, rototilled, and watered-in immediately to the
depth of desired control (approximately 4 to 6
inches). Approximately seven days after treatment,
the area should be cultivated to help release any
residual gases. One-to-two weeks later (two to three
weeks after initial application), the treated area may
be planted. The longer waiting period before
planting, and the lowered effectiveness without a
cover, are drawbacks to metham and should be
considered before use. The oral LD50 of metham is
820 mg/kg while the dermal LD50 is 2000 mg/kg.
Dazomet. Dazomet recently has been introduced
as a soil fumigant. Unlike methyl bromide and
metham, dazomet is a granular product and is not a
restricted use product. Being a granular, dazomet
must be evenly applied and incorporated for
maximum effectiveness. Its breakdown characteristics,
application preparation, and effectiveness are closely
associated to metham, as well as its advantages and