Agriculture: Floriculture and Ornamental Nurseries Pest Management Guidelines

Herbicide Treatment Table for Containers and Field-Grown Trees and Shrubs

Common name Amount to use REI‡ PHI‡
(Example trade name) (hours) (days)
Not all registered pesticides are listed. The following are listed alphabetically. When choosing a pesticide, consider information relating to resistance management, the pesticide's properties, and application timing. Tank mixes may be necessary to achieve desired control; see the table SUSCEPTIBILITY OF WEEDS TO HERBICIDE CONTOL for information on control of specific weeds. Always read the label of the product being used.
 
Note: Not all ornamentals will tolerate each herbicide. Check the label for species selectivity.
 
PREEMERGENCE HERBICIDES
A. DICHLOBENIL
  (Casoron 4G) See label 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 14
  COMMENTS: Not for container-grown ornamentals. Check label carefully for sensitive crops. A dormant season application of dichlobenil can control many seed-propagated, perennial, broadleaf weeds and provide residual control through early summer. Good for control of Equisetum and mugwort.
 
B. DIMETHENAMID-P
  (Tower) See label 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1:15
  COMMENTS: Mix with isoxaben or pendimethalin to expand the weed spectrum controlled. Can be used over the top on well-rooted plants. Check label for sensitive crops and test on a small group of each crop before applying widely.
 
C. DITHIOPYR
  (Dimension 2EW) See label 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 3
  COMMENTS: For application to established container and field-grown, tolerant ornamentals as listed on the label.
 
D. FLUMIOXAZIN
  (Broadstar, granular) See label 12 NA
  (Sureguard, sprayable) See label 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 14
  COMMENTS: Avoid contact with foliage of young crop plants. Wash foliage as soon as possible after application. Can cause stem dieback or leaf burn on sensitive plants. Has some postemergence activity. Provides moderate liverwort control. Helps provide preemergence control of annual grasses, chickweed, hairy fleabane, horseweed, and other annual broadleaves. Test on a small number of plants before using widely.
 
E. INDAZIFLAM
  (Marengo G) See label 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 29
  COMMENTS: Not for use on certain field-grown trees and shrubs; check label for permitted uses. Long residual. Irrigate immediately following application for best activity. Can be used on many ornamentals and also used around beds and greenhouses for long-term, preemergence, weed control.
 
F. ISOXABEN
  (Gallery SC) See label 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 21
  COMMENTS: Excellent herbicide for broadleaf weed control. Does not control annual grasses and willowherb, therefore often it is mixed with oryzalin or trifluralin to control grasses. It is safe on a wide range of woody ornamentals.
 
G. METOLACHLOR
  (Pennant Magnum) See label 24 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 15
  COMMENTS: Controls yellow nutsedge as well as some annual grasses, but to be effective it must be incorporated into the soil where nutsedge germinates and grows through the treated area. Check label for crop safety. This herbicide is one of the more soluble products (solubility 490 ppm) – make sure that it does not move with irrigation or rainwater.
 
H. NAPROPAMIDE
  (Devrinol DF-XT) See label 24 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 15
  COMMENTS: Needs mechanical incorporation (such as a power tiller, adequate irrigation, or 1 to 2 inches of rainfall within 2 to 3 days) for optimum results. The first irrigation seems to be critical for maximum activity. Safe on many woody plants but is weak in controlling some broadleaf weeds such as members of the aster and nightshade families, oxalis, and spurge. An excellent grass herbicide and can suppress common groundsel. Generally less efficacious but often safer than the combination herbicides, it is useful in herbaceous crops. Unless it is applied before rooted liners are established, injury is rare. If placed in the container around the newly planted liner before an irrigation settled the soil or if placed in the root zone, injury (stunting) may result. If the soil is moist and there is no rainfall or irrigation within 7 days following application, an appreciable amount of the herbicide is lost and weed control will be lessened.
 
I. ORYZALIN
  (Surflan AS) See label See label NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 3
  COMMENTS: A relatively broad-spectrum preemergence herbicide that does not need mechanical incorporation. Controls germinating seeds of annual grasses and many broadleaf weeds and can be used safely around many herbaceous and woody ornamentals. Leaches slightly into the soil from rainfall or irrigation. Can cause girdling of certain gymnosperms at the soil line: young hemlocks or firs (Abies spp.) up to about 3 years of age are affected, but arborvitae, junipers, pines, and Taxus are more tolerant. Stems of Monterey pines may exhibit some swelling. Oryzalin is a strong root inhibitor but most broadleaf ornamentals are very tolerant to oryzalin if the herbicide is not in the root zone. Commonly used in combination with other herbicides to widen the weed spectrum controlled.
 
J. OXADIAZON
  (Ronstar G) See label 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 14
  COMMENTS: Not for use in conifer nurseries or on certain weeds species; see label. A broad-spectrum preemergence shoot-girdling herbicide. In containers, granular oxadiazon plus napropamide is a good combination with a broad range of safety in woody plants. The wettable powder formulation should not be applied over young growth. Oxadiazon does not control weeds in the chickweed family but napropamide controls those. Has a relatively long residual, 12–16 weeks. Oxadiazon is not very effective on certain broadleaves including chickweed, horseweed, and pearlwort. Oxadiazon is very effective when applied in fall or spring. Oxadiazon does not leach readily in the soil, is not a root inhibitor, and thus is less likely to injure established species. Injury may occur if oxadiazon is applied to wet foliage, is not washed from the foliage, or the granules collect in leaf bases or crowns. If treated soil is cultivated, weed control effectiveness is reduced.
 
K. OXYFLUORFEN
  (Goal 2XL) See label 24 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 14
  COMMENTS: For use only around conifers and selected deciduous trees grown in the field. Excellent in dormant or hardened conifers where groundsel, malva, mustards, or purslane are found. Controls these weeds in a few days and provides residual, broadleaf control. Oxyfluorfen cannot be safely sprayed over most deciduous plants. Safest to the conifers when applied as granules. Weak on common chickweed, grasses, and horseweed. Oxyfluorfen acts by girdling the stem of seedlings; thus in soil, oxyfluorfen is most effective with frequent irrigation. If treated soil is cultivated, weed control is reduced.
 
L. PENDIMETHALIN
  (Pendulum 2G, Pendulum AquaCap) See label 24 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 3
  COMMENTS: Do not apply Pendulum AquaCap over the top of transplants; see label. Gives excellent grass control and controls many broadleaf weeds. Weed spectrum controlled is similar to that of oryzalin. Often combined with an additional herbicide to widen spectrum of weeds controlled. Controls oxalis and spotted spurge. An encapsulated formulation (AquaCap) has no odor and less persistent orange color. Though it is a root inhibitor, it is less injurious to roots than oryzalin or prodiamine.
 
M. PRODIAMINE
  (Barricade) See label 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBER: 3.
  COMMENTS: Stable on the soil surface. Does not provide as long of weed control as oryzalin at the maximum label rates for both. Has been less effective for groundsel and spurge suppression than some other dinitroaniline herbicides. Inhibits root growth. Low water solubility and does not move deeply in the soil.
 
N. TRIFLURALIN
  (Lebanon Treflan) See label 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 3
  COMMENTS: In the same class of herbicides as oryzalin (dinitroanilines), but it is not as stable on the soil surface. Must be incorporated with cultivation or irrigation or covered with a mulch very soon after application. Inhibits root growth. Often mixed with other herbicides (benefin or isoxaben) to widen the weed spectrum controlled.
 
PREEMERGENCE COMBINATIONS
Note: For tank mixes, observe all directions for use on all labels, and employ the most restrictive limits and precautions. Never exceed the maximum active ingredient (a.i.) on any label when tank mixing products that contain the same a.i.
A. DIMETHENAMID-P/PENDIMETHALIN
  (FreeHand 1.75G) See label 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBERS1: 15/3
  COMMENTS: Controls many common nursery weeds such as eclipta, oxalis, spurges, and willowherbs. Can be applied very soon after potting. Provides preemergence control or suppression of yellow nutsedge.
 
B. ISOXABEN/TRIFLURALIN
  (Snapshot 2.5 TG) See label 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBERS1: 21/3
  COMMENTS: Gives broad-spectrum control of annual broadleaf and grass weeds. Apply only to soil where established weeds have been removed. If the soil has been freshly cultivated, apply only after the soil has settled, then follow with an irrigation.
 
C. ORYZALIN/OXYFLUORFEN
  (Rout) See label 24 NA
  WSSA MODE-OF-ACTION GROUP NUMBERS1: 3/14
  COMMENTS: Provides excellent broad-spectrum control of annual broadleaf and grass weeds. Can be applied after a cultivation to reduce subsequent germination. Water in after application. If granules remain in plants at the base of the leaf or in whorls, burn will occur. Residual control is 3–4 months.
 
D. OXYFLUORFEN/PENDIMETHALIN
  (OH2) See label 24 NA
  WSSA MODE-OF-ACTION GROUP NUMBERS1: 14/3
  COMMENTS: Provides excellent broad-spectrum control of annual broadleaf and grass weeds. Should be watered-in immediately after application. Slightly less root pruning than the oryzalin/oxyfluorfen formulation (Rout). Residual control is about 3 months.
 
E. OXYFLUORFEN
  (Goal 2XL) See label 24 NA
  . . . PLUS . . .
  OXADIAZON
  (Ronstar Flo) See label 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBERS1: 14/14
  COMMENTS: Not currently registered in California for use on annual bluegrass, annual sedge, bristly oxtongue, cheeseweed, fiddleneck, fireweed, shepherd's-purse, sow thistle, ripgut bromegrass, and wild oats. Gives broad-spectrum control of grasses and broadleaf weeds. Soil should be thoroughly settled after cultivation and rainfall or irrigation because the products form a surface barrier that controls seedlings as they germinate and grow through the herbicides. Cultivation after treatment destroys the control.
 
F. PRODIAMINE/OXYFLUORFEN
  (Biathlon) See label See label NA
  WSSA MODE-OF-ACTION GROUP NUMBERS1: 3/14
  COMMENTS: See the comments above on these herbicides individually.
 
Selective (broadleaves)
A. OXYFLUORFEN
  (Goal 2XL) See label 24 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 14
  COMMENTS: For use only around conifers and selected deciduous trees grown in the field. Postemergence applications of oxyfluorfen will control certain annual broadleaf weeds. Effective only on certain young seedling weeds, especially little mallow. Perennial broadleaf weeds will be burned but not controlled. Activity is enhanced if a surfactant or crop oil is added. Spruces and true firs are injured by oxyfluorfen during their early flush but after about 5 weeks of new growth, they are tolerant. Dormant applications do not cause injury.
 
Selective (grasses)
A. CLETHODIM
  (Envoy Plus) See label 24 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 1
  COMMENTS: Controls most annual grasses, including annual bluegrass.
 
B. FLUAZIFOP-P-BUTYL
  (Fusilade II) See label 12 NA
  (Ornamec Over-The-Top) See label 4 See COMMENTS
  WSSA MODE-OF-ACTION GROUP NUMBER1: NC
  COMMENTS: Do not apply to ornamentals that may be harvested for food within 1 year after application. Kills most annual and perennial grasses; however, it will not control annual bluegrass or hard fescue. Most effective on young, actively growing grasses and less effective on mature grasses. Has injured certain azalea cultivars, especially at high rates, causing spotting and necrosis on leaves. Certain junipers also are sensitive to fluazifop-p-butyl; consult the label carefully.
 
Nonselective
A. CAPRYLIC ACID/CAPRIC ACID
  (Suppress) See label 24 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: NC
  COMMENTS: Works best on newly emerged weeds. Do not apply through any type of irrigation system.
 
B. CITRIC ACID/CLOVE OIL
  (BurnOut) See label 0 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: NC
  COMMENTS: Do not directly spray or allow to drift to desirable plants.
 
C. CLOVE OIL
  (Matratec) See label 0 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: NC
  COMMENTS: For use in and around greenhouses. Do not directly spray or allow to drift to desirable plants.
 
D. DIQUAT
  (Reward) See label 24 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 22
  COMMENTS: Not for use in ornamental seed crops in California. Labeled for use around container-grown ornamentals. Kills annual weeds, but only burns off the top of perennials. Contact activity only; affects only green tissue. Good for weed control in winter.
 
E. FATTY ACIDS/AMINE SALTS
  (Finalsan Herbicidal Soap) See label 24 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: NC
  COMMENTS: For around field-grown ornamentals. Do not directly spray or allow to drift to desirable plants.
 
F. GLUFOSINATE
  (Finale) See label 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 10
  COMMENTS: For use as a directed spray around container-grown ornamentals and established field-grown ornamentals. Do not apply directly to or allow to drift to desirable green tissue or thin or uncalloused bark. Contact herbicide with a limited amount of systemic activity; kills annual weeds, but only burns off the tops of perennials.
 
G. GLYPHOSATE
  (Roundup Pro) See label 4 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 9
  COMMENTS: Labeled for use around container-grown ornamentals and established woody ornamentals. A systemic herbicide that translocates to the roots and growing point of plants and kills the entire plant. Effective on both annual and perennial weeds. Contact with leaves of the ornamentals will result in injury to the plant. Glyphosate activity is increased in low water volumes. For example, greater activity is obtained at 20 gal/acre than at 50 gal/acre. This herbicide can be used alone or combined with a preemergence herbicide.
 
H. PARAQUAT*
  (Gramoxone SL 2.0) See label 24 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 22
  COMMENTS: For use as a directed around established field-grown ornamental trees. Do not apply directly to or allow to drift to desirable green tissue or bark. Kills annual weeds, but only burns tops off perennials. Controls young annual weeds with contact activity only and affects only green tissue.
 
I. PELARGONIC ACID
  (Scythe) See label 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 26
  COMMENTS: Labeled for use around container-grown ornamentals. Works by contact activity only (does not move in plants) and affects only green tissue. Good control of young annual weeds, but only burns off the top of perennials. Must be applied at high rates in high volumes of water. Very rapid activity.
 
1 Group numbers are assigned by the Weed Science Society of America (WSSA) according to different modes of action. Although weeds may exhibit multiple resistance across many groups, mode-of-action numbers are useful in planning mixtures or rotations of herbicides with different modes of action. For more information, see http://www.hracglobal.com.
Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
* Permit required from county agricultural commissioner for purchase or use.
NA Not applicable.
Text Updated: 07/20