Agriculture: Floriculture and Ornamental Nurseries Pest Management Guidelines

Herbicide Treatment Table for Field-Grown Flowers

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 environmental impact, 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 CONTROL for information on specific weed control. Always read the label of the product being used.
 
PREEMERGENCE HERBICIDES
A. ISOXABEN
  (Gallery 75DF) See label 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 21
  COMMENTS: Excellent herbicide for broadleaf weed control. Major weakness is annual grass control. Therefore, it is often mixed with oryzalin or trifluralin. Some broadleaf weed species can be controlled for up to 18 months with the labeled rates. Isoxaben does not effectively control Malvaceae (mallows). Some herbaceous ornamentals such as Digitalis, snapdragon, and Veronica may be killed by postplant, preemergence applications of isoxaben.
 
B. NAPROPAMIDE
  (Devrinol DF-TX Ornamental) See label 24 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 15
  COMMENTS: Works best if mechanically incorporated or followed by rainfall or a sprinkler irrigation of 1/2 inch within 7 days after application. The first irrigation seems to be critical for maximum activity. It is an excellent grass herbicide and can suppress common groundsel. Generally less efficacious but often safer than the combination herbicides. Is safer if applied after transplanting. 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.
 
C. ORYZALIN
  (Surflan AS Specialty) See label 24 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 3
  COMMENTS: A relatively broad-spectrum preemergence herbicide. Can be applied up to 21 days prior to rainfall or before irrigation that is needed to move it into seed zone. Needs 1/2 inch of irrigation or rain to move it to appropriate depth. Controls annual grasses and many broadleaf weeds and can be used safely on some crops after transplanting. Leaches slightly into the soil with irrigation or rainfall. A strong root inhibitor. Many broadleaf ornamentals are tolerant to oryzalin if the herbicide is not in the root zone. Even when applied at rates of 4 lb a.i./acre, sometimes weeds in the aster family (common groundsel, fleabane, prickly lettuce, sowthistle), mustard family (bittercress), and legume family (burclover) are not completely controlled. For most labeled weeds, control usually is effective for 2–3 months. Oryzalin can control spotted oxalis and spurge from seed for about 4 months. Tolerance is marginal on some crops; thus, use low rates until familiar with the herbicide and crop combination.
 
D. OXADIAZON
  (Ronstar G) See label 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 14
  COMMENTS: A broad-spectrum preemergence herbicide that is used during the growing season from spring until fall. It is moved off crop foliage and into the soil by a sprinkler irrigation following application. Oxadiazon is a shoot-girdling herbicide. The granular formulation is safer than the wettable powder. It is weak on all of the chickweed family and on certain broadleaves including chickweed, horseweed, and pearlwort. Has a relatively long residual, 12–16 weeks, but if cultivated control will be lost. It is very effective when applied in fall or spring. 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 applied to wet foliage, if it is not washed from the foliage, or if the granules collect in leaf bases or crowns.
 
E. PENDIMETHALIN
  (Pendulum 2G) See label 24 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 3
  COMMENTS: Gives excellent grass control and will control many broadleaf weeds. Controls a broad-spectrum of broadleaf and grass weeds that is similar to what oryzalin controls. It is often combined with an additional herbicide to widen the spectrum of weeds controlled. Though it is a root inhibitor, it is less injurious to roots than oryzalin or prodiamine.
 
F. PRODIAMINE
  (Barricade) See label 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 3
  COMMENTS: Prodiamine is stable on the soil surface. It also has been less effective for spurge and groundsel suppression than some other dinitroaniline herbicides. Inhibits root growth.
 
G. 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 and must be incorporated with cultivation or irrigation. At low rates trifluralin has been used as a preplant incorporated herbicide for some direct-seeded crops but is safer for use before transplanting.
 
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. ORYZALIN/OXYFLUORFEN
  (Rout) See label 24 NA
  WSSA MODE-OF-ACTION GROUP NUMBERS1: 3/14
  COMMENTS: Limited registrations for field-grown flowers. Woody plants are more tolerant than herbaceous plants. Provides excellent broad-spectrum control of annual broadleaf and grass weeds. If granules remain in plants at the base of the leaf or in whorls, burn will occur. Residual control is 3–4 months.
 
POSTEMERGENCE HERBICIDES
Nonselective
A. DIQUAT
  (Reward) See label 24 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 22
  COMMENTS: Labeled for use as a preplant treatment and directed postemergence use in field grown ornamentals. Kills annuals weeds, but only burns off the top of perennials. Controls young annual weeds with contact activity only; affects only green tissue.
 
B. GLYPHOSATE
  (Roundup Pro) See label 4 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 9
  COMMENTS: Labeled for use before planting. A systemic herbicide that translocates to the roots and growing point of the 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. Can be used alone or combined with a preemergence herbicide. Often takes 7 or more days after application for complete control. Avoid drift.
 
C. PARAQUAT*
  (Gramoxone SL 2.0) See label 24 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 22
  COMMENTS: For harvest aid and desiccation applications, preplant or preemergence (broadcast or banded), and postemergence directed spray. Controls young annual weeds with contact activity only; affects only green tissue.
 
D. PELARGONIC ACID
  (Scythe) See label 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 26
  COMMENTS: Labeled for use preplant. Controls young annual weeds by contact activity only; affects only green tissue. Must be applied at high rates in high volumes of water. Kills annual weeds, but only burns off the top of perennials. Does not move in plant. Very rapid activity (minutes in high sunlight).
 
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. Safe to use over most broadleaf ornamentals.
 
B. FLUAZIFOP-P-BUTYL
  (Fusilade II) See label 12 NA
  (Ornamec) See label 4 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 1
  COMMENTS: Postemergence contact selective herbicide for use in field grown ornamentals. Kills most annual and perennial grasses, however it will not control annual bluegrass or hard fescue. It is most effective on young actively growing grasses and less effective on mature grasses. Ornamec Over-The-Top not for use on certain ornamental species in California; see label.
 
C. SETHOXYDIM
  (Poast) See label 12 NA
  WSSA MODE-OF-ACTION GROUP NUMBER1: 1
  COMMENTS: Controls most annual grasses, except annual bluegrass or hard fescue. Most effective on young, actively growing grasses. A nonphytotoxic oil or nonionic surfactant must be added for best control.
* Permit required from county agricultural commissioner for purchase or use.
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.
NA Not applicable.
Text Updated: 07/20