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How to Manage Pests

UC Pest Management Guidelines

| More pests | More crops | About guidelines |

High-pressure tractor sprayer application to field sunflowers.

Floriculture and Ornamental Nurseries

Treatment for Field-grown Flowers

(Reviewed 3/09, updated 3/09)

In this Guideline: More about weeds in floriculture and ornamental nurseries:
Herbicide R.E.I.+
(commercial name) (hours)
When choosing a pesticide, consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
PREEMERGENT HERBICIDES
A. ORYZALIN
  (Surflan) 24
  WSSA MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: A relatively broad-spectrum preemergent herbicide that does not need mechanical incorporation. Controls annual grasses and many broadleaf weeds and can be used safely on some crops after transplanting. Leaches slightly into the soil with rainfall or irrigation. A strong root inhibitor. Many broadleaf ornamentals are very 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 Asteracae (common groundsel, sowthistle, prickly lettuce, fleabane), mustard (bittercress), and legume (burclover) families are not completely controlled. For most labeled weeds, control usually is effective for 2–3 months. Oryzalin can control spotted spurge and oxalis from seed for about 4 months. Tolerance is marginal on some crops; thus, use low rates until familiar with the herbicide and crop combination.
 
B. TRIFLURALIN
  (Treflan, and others) 12
  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.
 
C. PRODIAMINE
  (Endurance, Barricade) 12
  MODE OF ACTION: Unknown.
  COMMENTS: Prodiamine is stable on the soil surface. Does not provide weed control for as long as oryzalin at the maximum label rates for both. It also has been less effective for spurge and groundsel suppression than some other dinitroaniline herbicides. Inhibits root growth.
 
D. PENDIMETHALIN
  (Pendulum, etc.) 24
  WSSA MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Gives excellent grass control and will control many broadleaf weeds. Controls a broad-spectrum of grass and broadleaf weeds that is similar what oryzalin controls. Is often combined with an additional herbicide material to widen spectrum of weeds controlled. Though it is a root inhibitor, it is less injurious to roots than oryzalin or prodiamine.
 
E. NAPROPAMIDE
  (Devrinol) 12
  WSSA MODE OF ACTION GROUP NUMBER1: 15
  COMMENTS: Works best if mechanically incorporated or followed by rainfall or a sprinkler irrigation of 0.5 inch within 7 days after application. The first irrigation seems to be critical for maximum activity. 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.
 
F. OXADIAZON
  (Ronstar) 12
  WSSA MODE OF ACTION GROUP NUMBER1: 14
  COMMENTS: A broad-spectrum preemergent 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. Is weak on all of the chickweed family and on certain broadleaves including pearlwort, chickweed, and horseweed. Has a relatively long residual, 12–16 weeks, but if cultivated control will be lost. 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, however, if applied to wet foliage, if it is not washed from the foliage, or if the granules can collect in leaf bases or crowns.
 
G. ISOXABEN
  (Gallery) 12
  WSSA MODE OF ACTION GROUP NUMBER1: 21
  COMMENTS: Excellent material for broadleaf weed control. Major weakness is annual grass control. Therefore, it is often mixed with oryzalin or trifluralin. Isoxaben stunts seedlings by inhibiting cell wall formation in dividing cells. Some broadleaf weed species can be controlled for up to 18 months with the labeled usage rates. Isoxaben does not effectively control mallow and related species. Disadvantages are the cost and potential crop injury. Some herbaceous ornamentals such as snapdragon, Veronica, and Digitalis may be killed by postplant, preemergent applications of isoxaben.
 
PREEMERGENT 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 a.i. on any label when tank mixing products that contain the same a.i.
A. ORYZALIN/OXYFLUORFEN
  (Rout) 24
  WSSA MODE OF ACTION GROUP NUMBERS1: 3/14
  COMMENTS: A product with 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.
 
POSTEMERGENT HERBICIDES
Nonselective
A. GLYPHOSATE
  (Roundup Pro, Touchdown) see comments
  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 preemergent herbicide. Often takes 7 or more days after application for complete control. Avoid drift. Restricted entry interval for Roundup Pro is 4 hours and 12 hours for Touchdown.
 
B. PELARGONIC ACID
  (Scythe) 12
  WSSA MODE OF ACTION GROUP NUMBER1: 27
  COMMENTS: Labeled for use as a preplant treatment. 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 tops of perennials. Does not move in plant. Very rapid (minutes in high sunlight) activity.
 
C. PARAQUAT*
  (Gramoxone Inteon) 12
  WSSA MODE OF ACTION GROUP NUMBER1: 22
  COMMENTS: Can be used as a preplant treatment or around the perimeters of a nursery. Controls young annual weeds with contact activity only; affects only green tissue.
 
D. DIQUAT
  (Reward) 24
  WSSA MODE OF ACTION GROUP NUMBER1: 22
  COMMENTS: Labeled for use as a preplant treatment. Kills annuals weeds, but only burns off the tops of perennials. Controls young annual weeds with contact activity only; affects only green tissue.
 
Selective (grasses)
A. SETHOXYDIM
  (Poast) 12
  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.
 
B. FLUAZIFOP-P-BUTYL
  (Fusilade II, Ornamec) see comments
  WSSA MODE OF ACTION GROUP NUMBER1: 1
  COMMENTS: 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. Restricted entry interval for Fusilade is 12 hours and 4 hours for Ornamec.
 
C. CLETHODIM
  (Envoy) 4
  WSSA MODE OF ACTION GROUP NUMBER1: 1
  COMMENTS: Controls most annual grasses, including annual bluegrass. Safe to use over most ornamentals.
 
* 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 (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Floriculture and Ornamental Nurseries
UC ANR Publication 3392
Weeds
C. A. Wilen, UC IPM Program, UC Cooperative Extension, San Diego County
Acknowledgment for contributions to Weeds:
C. L. Elmore, Vegetable Crops/Weed Science, UC Davis

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