AL, oiniv. o FR sc
Dewayne L. Ingram and Wayne Currey
For Commercial Use Only
Florida Cooperative Extension Service/Institute of Food and Agricultural Sciences
Institute of Food and Agricultural Sciences/John T. Woeste, Dean for Extension
F >3& c.
Container Nursery Weed Control
Dewayne L. Ingram and Wayne L. Currey*
Weed control in container-grown ornamental crops
is one of the most important cultural concerns.
Weeds are plants growing where they are not wanted.
A plant can be a weed in one situation, and a
desirable plant in other situations. Weeds compete
with crop plants for space, water, light and nutrients.
One crabgrass plant in a one-gallon container can
reduce the growth of an Ilex crenata 'Convexa' liner
by 60 percent. However, even if weeds did not reduce
growth, a container plant with weeds is a less market-
able product than a weed-free product. Weeds also
harbor insects and diseases.
Although the predominant weed species change
from season to season in Florida, the amount of
pressure from these pest plants remains consistently
high. This publication provides information relative
to weed control principles, common weed plants, inte-
grated weed control programs and herbicide charac-
teristics, availability and use.
Common Weeds in Florida Nurseries
Weeds may be identified as grasses, broadleaves
or sedges. They may be further distinguished by the
length of their life cycle.
True grass weeds have hollow, rounded stems and
nodes (joints) that are closed and hard. The leaf
blades have parallel veins, are much longer than they
are wide and alternate on each side of the stem. Some
examples are crabgrass, goosegrass, crowfootgrass,
sandbur, annual bluegrass, torpedograss and vasey-
Broadleaf weeds are a highly variable group of
plants but most have showy flowers and net-like
veins in their leaves. They are easy to separate from
grasses due to their generally different leaf structure
and habits of growth. Some examples of broadleaf
weeds are cudweed, creeping charlie, henbit, spurges,
burning nettle, pennywort, creeping beggarweed,
cocklebur, sicklepod and Florida beggarweed.
Sedges are an important group of "grass-like"
weeds; however, they are not true grasses and are
characterized by a solid, triangular-shaped stem with
leaves extending in three directions. There are annual
sedges (often called water grasses), and the predomi-
nant and difficult to control perennial sedges. Of the
latter group, yellow nutsedge is yellowish green in
color and reproduces by seed, rhizomes and tubers.
The rhizomes radiate from the plant with a single
bulb or tuber the end of which may produce new
plants. Purple nutsedge is usually smaller in growth
habit than yellow nutsedge, has reddish purple seed
heads and produces a series of bulbs on radiating
rhizomes called "tuber chains."
The classification of weeds based on the length of
their life cycle may not be obvious on visual inspec-
tion but will have a great impact on the selection
and/or success of control procedures. The life cycle
characteristics will become an automatic association
as specific weeds and weed types are learned. The
three basic life cycles of weed plants are annual, bien-
nial and perennial.
Annual weeds, as the name implies, complete their
life cycle within one year. They germinate from seed,
grow, mature, produce seed and die in 12 months or
less. They may be annual grasses, sedges or broad-
leaved weeds. In addition, their life cycle may begin
at different seasons of the year. Thus, (a) summer
annuals emerge in the spring, mature, produce seed
and die before winter of each year. Weeds such as
crabgrass and cocklebur are typical of summer an-
nuals. Similarly, (b) winter annual weeds sprout from
seed in the fall and complete their life cycle before
summer of the next calendar year. Sowthistle, henbit,
annual bluegrass, and chickweed are examples of
winter annual weeds.
Compared to annual weeds, biennial weeds are few
in number. These weeds have a 2-year life cycle. They
*Dewayne L. Ingram is Associate Professor and Extension Horticulturist, Ornamental Horticulture Department, and Wayne L. Currey
is Associate Professor in Weed Science, Agronomy Department, IFAS, University of Florida.
germinate from seed in the fall and develop large root
systems and a compact cluster of leaves during the
first year. In the second year they mature, produce
seed and die. Examples of biennial weeds are cud-
weed, Carolina falsedandelion, wild carrot and bull
Weeds that live more than 2 years are perennials.
They reproduce by vegetative parts such as tubers,
bulbs, rhizomes (underground stems) or stolons
(above-ground stems). Some also produce seed in
addition to vegetative reproduction. During the
winter season most are dormant and many lose their
above-ground foliage and stems. In the spring they
initiate growth from food reserves in their root
systems. Torpedograss, nutsedge and various vines
are members of this group of weeds. Florida betony
is a perennial weed that, under a subtropical climate,
initiates its growth in the fall, grows during the
winter months and goes dormant during the heat of
Perennial weeds may be further divided into groups
based on the type of root system and reproductive
process. (a) Simple perennials reproduce by seeds but
root pieces distributed by cultivation or other
mechanical means will produce new plants. Florida
betony and some trees and shrubs are characteristic
of this group. (b) Bulbous perennials reproduce by
seed and above- or below-ground bulbs. Yellow nut-
sedge and wild onions have their bulbs below ground
while wild garlic has an above-ground bulb. The third
group is (c) creeping perennials which produce seed
but also produce rhizomes or stolons. Bermudagrass,
torpedograss and purple nutsedge produce these
specialized stems (rhizomes and stolons) that act as
food storage organs and can initiate growth at each
node (joint) along the stem. Obviously, perennial
weeds are the most difficult to control because of
their great reproductive potential and persistence.
Proper identification of target weeds is necessary
before effective control measures can be selected.
More information regarding identification of weeds
can be obtained from the county Extension office.
Weed Control Principles
Weeds are propagated from seed, root pieces or
special vegetative reproductive organs such as
tubers, corms, rhizomes or bulbs. Seed can be distrib-
uted by people, animals, birds, wind and/or water,
and are the most important weed source in Florida
nurseries. The other reproductive tissues and organs
listed must be moved mechanically to the container
by contaminated media, containers or liners.
Preventative weed control is the name of the game,
because control of established weeds in containers is
limited primarily to hand labor. Effective prevention
requires proper emphasis be placed on nursery sanita-
tion. Since seeds are the main weed source, reduction
in weed seed number in the production area should
be a high priority. Although some weed seeds are
wind-blown for several miles, most only move a short
distance. This means that elimination of seed-bearing
weeds adjacent to production areas would reduce the
weed seed population. Weeds that do develop in con-
tainers should not be allowed to set seed before they
are removed. Weed seed can also be distributed to
containers through irrigation water, especially if a
surface water source is used. Elimination of seed pro-
ducing weeds near surface waters can reduce this
problem. Irrigation system filters can remove many
weed seeds before they reach the containers.
Container media may contain weed seed or vegeta-
tive propagules. Contamination can occur before
media components are prepared and during mixing
or storage. Native peat may contain viable seed or
propagules even though it was dug from bogs 20 or
30 feet deep. Media should not be prepared or stored
in areas with a high weed population.
Rooted cuttings and seedlings transplanted from
propagation beds or containers can transfer weed
problems from the propagation area to production
areas. Therefore, it is essential that preventative
weed control start with the propagation phase of pro-
duction. If liners or seedlings are purchased, care
must be taken to ensure that only high quality weed-
free plants are brought into the production system.
It has been estimated that controlling weeds with
only hand labor would cost in excess of $6000 per acre
per year. This could account for up to 30 percent of
total production costs, without considering growth
reduction due to weed competition between weedings.
Although some hand removal of escape weeds may
be necessary, preventative weed control with herbi-
cides may account for as little as 3 percent of the total
production costs. Weed control for container nurs-
eries must start with clean production areas that are
kept clean through an integrated preventative
Weed Control Methods
Weed control can be accomplished by physical or
chemical means or by a combination of the two.
Mechanical weed control can consist of cultivation
or mowing of surrounding areas, plastic ground
covers on production beds and hand labor. Chemical
weed control consists of preemergence and postemer-
Weeds in nonproduction areas can be controlled by
cultivation, chemicals or competition from ground
covers. Cultivation is expensive and predisposes the
soil to erosion, especially on sloping areas around the
nursery. Cultivation within the container production
areas is impractical. Turfgrasses are tough competi-
tors for weeds if proper, yet low maintenance sched-
ules are followed. Turfgrass selection should be based
on seed production characteristics, tolerance of traf-
fic and nutrition, light and irrigation requirements.
Mulches in container production areas are used to
stabilize production bed surfaces and prevent weed
growth. Black plastic is by far the most common
ground cover. Although some weeds can penetrate
the plastic, most will not. Chemical pretreatment
under the plastic has proven to be helpful and will
be discussed in more detail in the next section. Some
woven plastic fabrics provide a barrier to weed
growth by reducing light but allow water penetra-
tion. Plastic materials will last from 1 to 3 years in
full sun production areas but ultraviolet light inhibi-
tors are required if plastic ground cover is to last
more than one year. Plastic ground covers may last
for more than 5 years in shaded production areas.
Gravel placed over black plastic film may be used,
but is expensive. Organic ground covers or mulches
such as pine bark, sawdust or cypress shavings break
down rapidly, provide a nice environment for weed
seed germination and may be moved easily by wind
Organic mulches can also be placed on the surface
of container media and provide short term weed con-
trol. Inorganic mulches, such as fiberglass discs, have
been evaluated by researchers, but due to economic
considerations and reduction in air exchange with the
media, the use of such mulches is limited.
Chemical weed control with herbicides has reduced
greatly the cost of weed control in Florida nurseries.
Annual herbicide costs are one-tenth that of hand
labor for weeding. Herbicides are a group of chemical
compounds that control plant growth and develop-
ment by interrupting some metabolic pathway or by
contact action. Plant response to these chemicals
depends largely on concentration of the chemical
applied. For example, 2,4-D can effectively control
broadleaf weeds but at lower concentrations this
chemical exhibits growth-regulating properties by
stimulating rooting of cuttings in certain cases.
Herbicides may be selective or nonselective
through chemical characteristics or rate adjustment.
Selective herbicides kill some plants with little or no
effect on other plants, while nonselective herbicides
are toxic to all plants. Herbicide screening research
identifies the selective rate range of these chemicals
to find compounds that are not toxic to crop plants
but that control many weed plants.
Some herbicides will kill only the plant tissue with
which they come in contact, while others are ab-
sorbed by the plant and transported within the plant
to kill all plant parts. Contact herbicides may kill the
foliage of perennial plants but regrowth from the
roots is likely. Translocated or systemic herbicides
affect the entire plant.
Preemergence herbicides prevent seedling emer-
gence and development and are applied to container
media surfaces and surrounding production areas
before weed emergence. Postemergence herbicides are
applied to existing weeds. Some herbicides have pre-
emergence and postemergence properties.
Herbicides are formulated as wettable powders (W
or WP), solutions (S) and granular (G) or emulsifiable
concentrates (E or EC). Granular herbicides are
applied dry to crop area. Solutions, wettable powders
and emulsifiable concentrates are mixed with water
and applied by a sprayer. Good agitation in the spray
tank is necessary to provide uniform application
rates. The amount of active ingredient in a herbicide
formulation is presented as a number in front of the
formulation designation (G, WP, EC, S) on the label.
For example, a 4 percent granular herbicide would
be identified as a 4G material, and there is 4 pounds
of active ingredient in 100 pounds of product. A 75
percent wettable powder is labeled as 75WP, which
means that 3 of 4 pounds of material in the bag is
active ingredient. Liquid formulations are labeled as
pounds of active ingredient per gallon of product. For
example, a 2EC contains 2 pounds of active ingredi-
ent per gallon of product.
Fumigants kill all living things in the soil including
weeds, weed seeds, insects, nematodes and disease
organisms. The nature of these chemicals makes
them extremely useful in the nursery industry for
preplant treatment, but most of them are hazardous
Selection of a herbicide should be based on the
weeds to be controlled, the existing weed population,
length of control desired and specific crop plants in-
volved. The following herbicide descriptions should
be helpful in choosing the proper material for a weed
control program. Always follow the label instructions
and restrictions. The following descriptions are not
recommendations, but are intended as background
Alachlor, Lasso, is available as 4EC and 15G. It
controls most annual grasses, pigweed, carpetweed
and purslane. Limited control of yellow nutsedge,
smartweed, seedling Johnsongrass and lamb's-
quarters has been noted. Overhead irrigation is re-
quired within one hour of application of this material
over ornamental plants. Alachlor is more readily
leached through container media than other
preemergence herbicides. Alachlor should not be used
Metolachlor, Dual, is available as 8EC and 25G and
when applied at the same rate should yield similar
results as alachlor, Lasso.
Oryzalin, Surflan, is available as a 75WP and will
prevent emergence of many grasses and broadleaf
weeds at 21/2 to 5 lbs of active ingredient per acre
(2.75 to 5.5 kg of active ingredient/ha). This nonvola-
tile herbicide can be applied in any season and is rela-
tively water insoluble. It will last 2 to 4 months
depending upon application rate. Oryzalin is not
absorbed and translocated by plants but can inhibit
plant root growth. Irrigation after application is
needed to activate the product.
Oxadiazon, Ronstar (2G) and Pro Gro Ornamental
Herbicide I (4G), is labeled for a wide range of
container-grown ornamentals. It controls most
nursery weeds, but has limited effect on spurges and
chickweed. It should not be broadcast on plants with
rosettes, whorls or wet foliage. Applications of 4
pounds of active ingredient per acre (4.4 kg of active
ingredient/ha) should be repeated every 10 to 12
Oxyfluorfen plus pendimethlin, Pro Gro Ornamen-
tal Herbicide II, is a 3G formulation labeled for use
on container-grown ornamentals. The two active
ingredients in a 2:1 ratio allow this product to control
a wide range of nursery weeds and be effective on
spurges. These two herbicides are also marketed
separately as Goal and Prowl. Applications of 3
pounds of combined active ingredient per acre (3.3
kg of active ingredient/ha) should be repeated every
10 to 12 weeks. Avoid broadcast application to plants
with rosettes, whorls or wet foliage as injury may
Oxyfluorfen plus oryzalin, Rout, is also a 3G formu-
lation labeled for use on field and container-grown
ornamentals. The active ingredients are Goal and
Surflan in a 2:1 ratio. Rout is registered on a wide
variety of ornamentals and gives preemergence con-
trol of a broad spectrum of weeds including spurges.
Apply 3 pounds of active ingredient per acre (3.3 kg
of active ingredient/ha) every 3 months during the
Trifluralin, Treflan, is marketed as 4EC and 5G
formulations. This volatile herbicide controls most
annual grasses and many broadleaf weeds at 1 to 4
pounds of active ingredient per acre (1.1 to 4.4 kg of
active ingredient/ha) and should be irrigated immedi-
ately after application. Trifluralin inhibits root
growth, but remains where it is applied with minimal
Napromide, Devrinol, is available in 5G, 10G and
50WP formulations. It is labeled for use on a wide
range of container-grown ornamentals. It is effective
for control of grasses but less effective on spurges
and certain broadleaf weeds. Application of 4 to 6
pounds of active ingredient per acre should be
repeated every 8 to 10 weeks.
Dichlobenil, Casoron and Norosac, should not be
used in containers because of its volatility and leach-
ability. However, it has been used as a pretreatment
to container production beds before putting down
black plastic or other physical barriers. Applications
of 4 to 6 pounds of active ingredient per acre (4.4 to
6.6 kg of active ingredient/ha) from the 10G formula-
tion of this herbicide are appropriate for this purpose.
Paraquat 2S kills plant foliage on contact and has
no residual activity in soil. The material is not
translocated and regrowth of perennial weeds is like-
ly. Paraquat can be applied as a directed spray, but
contact with green bark or suckers of some ornamen-
tal plants will cause injury. A nozzle shield will im-
prove selective placement. Rates of 0.25 to 0.50
pound of active ingredient per acre (0.275 to 0.55 kg
of active ingredient/ha) with a surfactant are recom-
mended. Paraquat is a restricted use pesticide in
Florida and extreme precaution should be taken to
prevent skin contact, inhalation of spray mist, soak-
ing of absorbent clothing or eye contact.
Glyphosate, Roundup, is a 4S formulation of a non-
selective translocated, postemergence herbicide.
Rates of 1 to 4 pounds of active ingredient per acre
in 20 to 50 gallons (1.1 to 4.4 kg of active ingredi-
ent/ha in 75 to 190 liters) of water will kill most ac-
tively growing plants. It is absorbed by green foliage,
stems and branches and translocated throughout the
plants. Six hours without rain is the recommended
term for maximum absorption. Roundup requires 3
to 10 days or more to kill most plants and a repeat
application may be required for plants with extensive
underground storage organs like nutsedge and ber-
mudagrass. Roundup is rapidly deactivated in soils;
therefore, a directed spray around crop plants is effec-
tive and replant delays are not necessary.
Fluazifop-butyl, Fusilade, and sethoxydim, Poast,
are postemergence grass herbicides. They are regis-
tered separately for over-the-top control of many
annual and perennial grasses. Consult the label for
registered ornamental species. Apply 0.125 to 0.50
pound of active ingredient per acre with a surfactant
or crop oil in 20 to 40 gallons per acre. While most
broadleaf plants are tolerant, certain varieties of
some plants, such as azaleas, have been injured at
high application rates. Poast has given excellent
annual grass control while Fusilade has been superior
on perennial grasses. Both products are rapidly ab-
sorbed into the grass leaf and rainfall or irrigation
within one hour has not reduced the control. No pre-
emergence soil activity is expected.
Chlor-O-Pic chloropicrinn), methyl bromide and
Vapam (liquid carbamate) are fumigants used for soil
treatment before planting. These materials are tox-
ic to all plants as well as insects, nematodes and
disease organisms. Because of the gaseous nature of
the chemicals, they must be applied under controll-
ed conditions such as under a sealed plastic film.
Temperature, time between treatment and trans-
planting and safety measures must be monitored.
Follow labels carefully.
Environmental conditions can change the activity
of herbicides or alter plant response to these chemi-
cals. The small volume to surface area of containers
exposes the medium and root system of container-
grown plants to wide temperature variations. Con-
tainer plants grown outdoors may receive up to 160
inches of water annually and excessive irrigation may
result in herbicide leaching.
Effective preemergence herbicides in containers
must remain in the top surface of the medium and
not move into the root zone. Most of these herbicides
will inhibit root growth if leaching occurs. Media con-
taining approximately 50% by volume pine bark
seem to hold herbicides in the surface layer more
effectively than peat and sand media components.
Wetting agents are applied to container media to
facilitate thorough wetting of peat and pine bark
particles. Since these materials decrease the surface
tension of water and allow more rapid water disper-
sion, their effects on herbicide leaching through the
depths of container media have been questioned.
However, in a preliminary study three wetting agents
did not increase leaching of trifluralin or oxadiazon
applied at recommended rates.
Enclosed structures such as greenhouses pose
serious limitations for herbicide use. One must be
concerned not only with phytotoxicity from direct
contact from chemicals but also with the volatility
of the chemicals in a partially closed system.
Herbicides are usually applied in liquid or granular
formulations. Most labeled preemergence herbicides
for container production are granular formulations
to ensure application to the medium surface with
limited foliar contact and drift. Most postemergence
herbicides are liquid formulations to facilitate
thorough weed coverage. General application proce-
dures and guidelines for equipment calibration for
granular and liquid herbicide formulations are
Granular. Herbicide Application
The use of granular herbicides (Ronstar, OH-1,
OH-2, Treflan, Lasso, etc.) in the production of con-
tainer ornamentals requires accurate application. A
properly calibrated Universal #75 spreader, such as
the Scotts ProGrow spreader, will assist in achieving
uniform coverage, but must be calibrated for each
operator and each granular herbicide (Figure 1). A
Fig. 1. A cyclone-type, Universal #75 spreader is often
used to apply granular herbicides to ornamental plants.
Table 1. Approximate Spreader Settings: Granular Herbicide Calibration
Rout and OH-2 Scotts
Treflan 5G (small)
Treflan 5G (large)
Lasso II 15G
in 88 feet*
1 quart (900 cc)
2 quarts (1800 cc)
0.6 quart (550 cc)
1.2 quarts (1100 cc)
1.2 quarts (1100 cc)
1.0 quart (950 cc)
1.4 quarts (1360 cc)
0.75 pint (350 cc)
0.30 pint (160 cc)
Dual 25G 4.0 16 2.0 0.13 pint (66 cc)
*Because of the particle size, density and displacement volume of each granular herbicide formulation vary, the figures shown
in this column are approximate and vary slightly between materials. It is necessary to calibrate accurately for each granular material,
application rate and spreader setting.
periodic recheck of the calibration is desirable since
granule particle size, particle density, humidity,
human variability and wind can affect the accuracy
of application. In practical use, wind velocities of
greater than 5 mph severely distort the uniformity
of most applications and swath width.
The following is one of several calibration methods
and the spreader settings are only approximate and
may need adjustment to fit the desired rate.
Step 1: Calibrate walking speed to 3 mph (88 feet
in 20 seconds).
Step 2: Make one complete turn of the crank per
Step 3: Set front sliding gate completely open.
This will treat a 6- to 8-foot swath
(10-foot swath for large granules like
Treflan) depending on wind speed and
direction and granule density.
Step 4: Make spreader setting from approximate
value listed in Table 1. Set value to the
front edge of the flow control rod. Then
close the spreader flow gate.
Step 5: Add a known amount of granules (1 quart)
to the spreader to ensure proper flow
Step 6: Add the correct amount of granules for the
treated strip and make the 88-foot pass
under conditions stated in steps 1-4.
Step 7: At completion, measure to see if the origi-
nal known volume (1 quart) remains in
the spreader. Make any adjustments
necessary and repeat procedure.
Use of the information in Table 1 will result in
application of the indicated amount in one pass. Some
herbicide labels suggest two passes in opposite direc-
tions to ensure uniform coverage and ease of applica-
tion. The necessity for this depends on the size of the
ornamentals being treated and applicator skill.
A hand-held shaker can be utilized to apply granu-
lar herbicides to a small number of containers or to
extremely large containers (Figure 2). This method
may be useful for treating freshly potted plants while
Fig. 2. Hand-held shaker applicators can be used
effectively for treating a small number of containers or
individual, extremely large containers.
still on the trailer before they are spaced in the pro-
duction area. This could save time and chemicals and
ensure that preemergent herbicide applications were
made before weed emergence. After the amount of
surface area to be treated at one time has been deter-
mined, the recommended amount of herbicide can be
placed in the shaker and applied uniformly to the
area. Safety precautions should be followed rigidly.
Liquid Herbicide Application
Liquid formulations can be applied by wick applica-
tors, hand sprayers, backpack sprayers or vehicle-
mounted sprayers (Figure 3). Shielded spray nozzles
can be used to aid in proper placement of directed
sprays around crop plants. Specialized motor-driven
sprayers are now on the market with adjustable
Regardless of the type of sprayer used to apply
herbicides, the speed, pressure and nozzle height
must be kept constant for accurate application. When
using hand pump-up or lever-operated knapsack
sprayers with a single nozzle wand, a pressure gauge
should be added to monitor the operating pressure.
The nozzle should be held at a height to apply a
12-inch swath to the sprayed surface. Most impor-
tant is the walking speed of the applicator. The appli-
cator should practice a constant walking speed over
a measured course before spraying. A walking speed
of 44 feet in 15 seconds equals 2 mph. Adjust the
operating pressure between 1 and 25 psi and catch
the flow from the nozzle in 15 seconds. A flow rate
Fig. 3. Liquid formulation of herbicides are com-
monly applied by wick applicators, pump-up hand-
sprayers and backpack sprayers.
yielding 2.5 oz (75 ml) during 15 seconds is equal to
20 gallons per acre and 5 oz (150 ml) in 15 seconds
is equal to 40 gallons per acre. Following these condi-
tions will give adequate spray coverage to the target
Always clean the sprayer thoroughly after applica-
tion with soap and water. Household ammonia should
also be used following application of 2,4-D-type herbi-
cides. It is a good idea to designate one sprayer for
herbicides only and not use it to apply any other type
This publication was produced at a cost of S1.669.46. or 48 cents per copy. to inform the nursery industry of prin-
ciples of weed control and identify specific methods of weed control, including mechanical, cultural and chemical.
COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLORIDA, INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES, ICR. Teertiller,
director, in cooperation with the United States Department of Agriculture, publishes this information to further the purpose of the May 8 and
June 30,1914 Acts of Congress; and is authorized to provide research, educational information and other services only to individuals and institu-
tions that function without regard to race, color, sex o national origin. Single copies of Extension publications (excluing 4-H and Youth publca-
tions) are available free to Florida residents from County Extension Offices Information on bulk rates or copies for t-of-te purchasers is
available from C.M. Hinton, Publications Distribution Center, IFAS Building 664, University of Florida, Gainesvile, Florida 32611. Before publicizing this publication,
editors should contact this address to determine availability.