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“Dirty Deeds Done Dirt Cheap- er” - Nursery Container Weed Control
Hannah Mathers
For: GLTE
Website: basicgreen.osu.edu
If your nursery container weed control program is working optimally, the only time you
should need to hand weed would be 1-2 days before each herbicide application. Your
scheduled applications would be in the spring, summer and fall for most Midwest container
nurseries. Sometimes, however, seed before a scheduled application, requiring supplemental
hand-weeding and a half rate preemergence herbicide application to re-establish the chemical
barrier in the top half of soilless media.
The major cost of your container weed control program is labor to hand-weed when
your preemergence herbicides fail. The relative cost of the pre- and post- herbicides is small
by comparison to labor. Reducing your hand-weeding to those events indicated above, with
the best herbicides, methods and timings are essential to saving money. The cost of
herbicides, however, also includes labor for the application. The number of applications can
be reduced via new methods and equipment. Applying at the correct time will also reduce your
application costs by increasing the efficacy of the application.
When Are Preemergence Herbicides Effective?
Many of the preemergence herbicides used in ornamentals must be applied before
weed seeds germinate as they are inhibitors of microtubule assembly, Weed Science Society
of America (WSSA) Group 3 herbicides. The germinating seed must contact the top layer of
the container media surface where the Group 3 herbicide, such as the dinitoanaline herbicide
family, has been incorporated. If the seed is not in contact with the incorporated layer
germination will not be inhibited. Some non-Group 3 preemergence herbicides, however, will
kill “small” weeds post-germination. These exceptions are Goal (oxyfluorfen) and SureGuard
(flumioxazin) which are Group 14, protoporphyrinogen oxidase (PPO) inhibitors. PPOs are
found in the plant chloroplast and their inhibition leads to (among other things) lack of a
precursor of chlorophyll. PPO inhibitor damage can appear as leaf crinkling and malformation
from the rapid destruction of the contacted tissue. Gallery is another ornamental
preemergence herbicide that can kill “small” weeds. Gallery (isoxaben) is a Group 21
herbicide that includes the herbicide family benzamide. Benzamides inhibit cell wall synthesis
causing mottling and random leaf chlorosis on susceptible contacted plants. In general, if even
small weeds are present at time of application, unless the product you are applying contains
oxyfluofen, flumioxazin and/ or isoxaben alone or in combination, your preemergence
applications will be unsuccessful. Again, Group 3 herbicides such as Barricade 65WG
(Prodiamine); Pendulum 2G, Pendulum 3.3 EC, Pre-M 60DG, Pre-M 3.3 EC, or Corral
(Pendimethalin); Surflan T/O (Oryzalin); Treflan 5G or Trifluralin EC (Trifluralin); Dimension
(Dithiopyr) or Dacthal (DCPA) “must” be applied and incorporated preemergence!!
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Star Trek and the Q Continuum: Nurseries and the Weed Emergence Continuum!
There are two big times in container nursery weed control based on weed life cycles,
namely the emergence of summer and winter annuals. These two life cycles dictate, two of
the three “scheduled” herbicide applications noted in the introduction. Summer annual (SA)
weeds germinate in spring and die by winter, such as lamb’s-quarters (Chenopodium album)
or Common Purslane (Portulaca oleracea) (Table 1). Preemergence herbicides need to be
applied and incorporated in mid to late March or following the removal of the poly-coverings
from the overwintering houses to control the SAs. Winter annual (WA) weeds germinate in fall,
overwinter as seedlings and set seed and die in the summer, such as shepherd’s purse
(Capsella bursa-pastoris) or Pennsylvania bittercress (Cardamine pensylvanica) (Table 1).
Preemergence herbicides need to be applied and incorporated by mid to late August or prior to
applying the poly coverings to the overwintering houses (September to November) to control
WAs.
As with any continuum some winter annuals are emerging before their counterparts ex.
Marestail (Table 1) and some summer annuals after their counterparts ex. Prostate or spotted
spurge and Purslane. To control Marestail herbicides need to be out and incorporated by early
August. To control Prostrate or spotted spurge and Purslane preemergence herbicides need
to be applied in June when temperatures are raising to levels adequate to germinate these
weed species. Because these late and early emergence weeds are not fitting into the
“scheduled” application times it is understandable that the herbicides that control them best are
products that are or contain oxyfluofen, flumioxazin and/ or isoxaben. The best herbicides for
spurge control are oxyfluofen combination products (Rout or OHII) or Goal alone (Goal
Tender). A new herbicide by Bayer and distributed by OHP Biatholon (oxyfluorfen +
prodiamine will also provide control. BroadStar (flumioxazin) has also been shown to be very
effective for spurge control. The best herbicide for marestail is BroadStar or SureGuard
(flumioxazin). In fields it is best to combine with glyphosate to ensure burn down of any
germinated seedlings.
Table 1. Common nursery weeds listed by family and life cycle (Source: Altland 2003; Gilliam
et al. 1990; Norcini and Stamps, 1994).
Common name
Smooth pigweed
Redroot pigweed
Silver thread
mosses
Hairy bittercress
Pennsylvania
Scientific name
Amaranthus
hybridus
Amaranthus retrofl
exus
Bryum argenteum
Division or family
Amaranthaceae
Life cycle
Summer annual
Amaranthaceae
Summer annual
Bryophyta
Perennial
Cardamine hirsuta
Cardamine
Brassicaceae
Brassicaceae
Winter annual
Winter annual
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bittercress
Prostrate spurge
Horseweed or
marestail
Yellow nutsedge
Large crabgrass
Eclipta
Northern willowherb
Mulberry weed
Ground ivy
Prickly lettuce
Henbit
Liverwort
Creeping red
woodsorrel
Longstalked
phyllanthus
Annual bluegrass
Common purslane
Birdseye pearlwort
Common groundsel
Annual sowthistle
Common chickweed
Dandelion
pensylvanica
Chamaescyce
maculata
or Eurphorbia
maculata
Conyza canadensis
Eurphorbiaceae
Summer annual
Asteraceae
Summer or winter
annual
Perennial
Summer annual
Summer annual
Summer annual
Summer annual
Perennial
Cyperus esculentus
Digitaria sanguinalis
Eclipta prostrata
Epilobium ciliatum
Fatoua villosa
Glechoma
hederacea
Lactuca serriola
Cyperaceae
Poaceae
Asteraceae
Onagraceae
Moraceae
Lamiaceae
Lamium
amplexicaule
Marchantia
polymorpha
Oxalis corniculata
Labiatae
Phyllanthus tenellus
Euphorbiaceae
Poa annua
Portulaca oleracea
Sagina procumbens
Senecio vulgaris
Sonchus oleraceus
Stellaria media
Poaceae
Portulacaceae
Caryophyllaceae
Asteraceae
Asteraceae
Caryophyllaceae
Taraxacum offi
cinale
Asteraceae
Asteraceae
Hepatophyta
Oxalidaceae
Winter or summer
or biennial
Summer or winter
annual
Perennial
Perennial (spreads
by stolons)
Perennial
Winter annual
Summer annual
Perennial
Winter annual
Summer annual
Summer or winter
annual
Perennial
Other weeds that don’t fit the “scheduled” herbicide applications are those that are dose
responsive such as Crabgrass and Bittercress. Products such as OHII or BroadStar versus
Snapshot have been shown to provide sufficient residual to control these dose responsive
weeds. FreeHand 1.75G a new herbicide from BASF (Dimethenamid- p + pendimethalin )
applied at 150 lb/ac is another option for dose response weeds. FreeHand is proving to be an
excellent, broad-spectrum weed control and at 150 days of control it is one of the longest-
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lasting preemergence herbicides in container nurseries. Because it is a continuum of weed
emergence and of weed species, combination herbicide products are often superior. Not only
because they contain one of the three “burn-down” potential herbicides for seeds already
germinated at time of application, but they also usually contain grass and broadleaf active
herbicides (Table 2). Table 2 lists the most commonly used nursery container granular
preemergence herbicides.
Table 2. Granular preemergence herbicides registered for use in nursery containers. Note
many are combinations of products that have selectivity on broadleaf and grasses in order to
increase their spectrum and flexibility of control. BroadStar is the only granule listed below that
control broadleaf and grassy weeds with a single active (flumioxazin).
Trade Name
Rout
Regal 0-0
Showcase
Jewel
Harrell’s 75 or 63
Corral
Snapshot 2.5 TG
Pendulum 2G
Barricade 65WG
Treflan 5G (TR10)Ronstar G
Regal Star G
OH2
Devrinol 2G
XL 2G
Broadstar
Freehand
Biatholon
Common Name
Broadleaf active
Grass active
Oxyflourfen
Oxyflurofen
Isoxaben + Oxyflurofen
Oxadiazon
Oxyfluorfen
+
+
+
+
+
Isoxaben
+
Oxadiazon
Oxadiazon
Oxyflourfen
Napropamide
+
+
Oryzalin
Oxadiazon
Trifluralin
Pendimethalin
Trifluralin
Pendimethalin 2.68G
Trifluralin
Pendimethalin
Prodiamine
Trifluralin
Prodiamine
Pendimethalin
Oryzalin
Flumioxazin (broad spectrum)
Dimethenamid- p
+
Oxyfluorfen
+
Pendimethalin
Prodiamine
Summary
As a general rule, for every pound of weed growth produced, about one less pound of crop
growth is produced. Usually, early weed competition reduces crop growth far greater than late
season weed growth. It naturally follows then, that early weed control is very important. Late
season weed growth is important in the container yard and is always important in reduction of
the seed bank for coming years.