UC IPM Online UC ANR home page UC IPM home page

UC IPM Home

SKIP navigation

 

How to Manage Pests

UC Pest Management Guidelines


Floriculture flower crops.

Floriculture and Ornamental Nurseries

Treatment for Field-grown Trees and Shrubs

(Reviewed 3/09, updated 3/09)

In this Guideline: More about weeds in floriculture and ornamental nurseries:

Herbicide R.E.I.+
(commercial name) (hours)

  Calculate impact of pesticide on air quality
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 germinating seeds of annual grasses and many broadleaf weeds and can be used safely around many woody ornamentals. Leaches into the soil with rainfall or irrigation. Can cause girdling of certain ornamentals at the soil line: young hemlocks are particularly susceptible to root inhibition and girdling from oryzalin. Seedlings of Douglas fir and true firs (Abies spp.) up to about 3 years of age are also affected, but pines, Taxus, arborvitae, and junipers are more tolerant. Stems of Monterey pines may exhibit some swelling. Often used in combination with other herbicides to widen weed spectrum controlled.
  Even at rates of 4 lb a.i./acre (4.4 kg/ha), it sometimes has not completely controlled weeds in the Asteraceae (common groundsel, sowthistle, prickly lettuce, fleabane), mustard (bittercress), and legume families. Control is usually for 1–2 months. For full-season control (1 year), re-treat in about 4 months. Re-treatment at about 3- to 4-month intervals, supplemented with some hand-weeding, has given control of most weeds.
 
B. TRIFLURALIN
  (Treflan, and others) 12
  WSSA MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Can be applied as a preplant incorporated, or postplant directed and incorporated treatment. 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, or covered with a mulch, very soon after application. Often mixed with other herbicides (isoxaben, benefin) to widen weed spectrum controlled.
 
C. PRODIAMINE
  (Endurance, Barricade) 12
  MODE OF ACTION: Unknown.
  COMMENTS: Prodiamine is a dinitroaniline that is stable on the soil surface. It will not provide as long weed control as oryzalin at the maximum label rates. Because of its low water solubility, it does not leach. It is a strong root inhibitor like oryzalin.
 
D. PENDIMETHALIN
  (Pendulum, etc.) 24
  WSSA MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Labeled for use in field-grown ornamentals. In most cases, pendimethalin will probably not control a broad enough spectrum of weeds to rely on it as a "stand alone" product. It should be applied in some combination with an additional material. Controls oxalis and spotted spurge. Available as a WDG and an encapsulated formulation, which has no odor and less orange staining.
 
E. NAPROPAMIDE
  (Devrinol) 12
  WSSA MODE OF ACTION GROUP NUMBER1: 15
  COMMENTS: Preemergent herbicide that 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. Safe on many woody plants but is weak in controlling some broadleaf weeds such as members of the nightshade and aster families, spurge, and oxalis. An excellent grass herbicide and can suppress common groundsel. Generally less efficacious but often safer than the combination herbicides, it is useful in the herbaceous market.
  Unless applied before rooted liners become established, injury is rare. If placed in the container around the newly planted liner before irrigation can settle 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.
 
F. METOLACHLOR
  (Pennant) 24
  WSSA MODE OF ACTION GROUP NUMBER1: 15
  COMMENTS: Controls yellow nutsedge as well as most annual grasses. To be effective, must be incorporated into the soil where nutsedge germinates and grows through the treated area. Granules of metolachlor are safe at all stages of growth. With pines and certain deciduous plants, over-the-top sprays of metolachlor should be on dormant stock, before budbreak. Metolachlor EC distorts plants. Metolachlor has been effectively combined with simazine, oxyfluorfen, or isoxaben for broad-spectrum weed control. One of the more soluable herbicides (solubility 490 ppm) so care must be taken that it does not move with irrigation or rainwater. Oryzalin and metolachlor combinations form an orange sludge in the tank so they should be applied in separate operations. If they must be tank-mixed, reduce this incompatibility by increasing spray volume to 80 GPA and by adding a "mix-aid" type of product.
 
G. OXADIAZON
  (Ronstar) 12
  WSSA MODE OF ACTION GROUP NUMBER1: 14
  COMMENTS: A broad-spectrum preemergent herbicide that is moved off the foliage and into the soil by an irrigation following application. Used during the growing season from spring until fall. Granular oxadiazon has broad safety in woody plants. The wettable powder formulation should not be applied over young growth. It can be applied as a directed spray to the base of the trees or shrubs. Has a relatively long residual, 12–16 weeks. Does not control chickweed and horseweed. Re-treatments are required at approximately 3- to 4-month intervals to maintain control throughout the season. Fall and spring applications of oxadiazon have been very effective.
  Oxadiazon does not leach readily in the soil, and thus injury has not resulted on many species evaluated in tests. Injury may occur, however if oxadiazon is applied to wet foliage, is not washed from the foliage, or the granules collect in the leaf bases or crowns. If treated soil is cultivated, weed control effectiveness is reduced.
 
H. OXYFLUORFEN
  (Goal) 24
  WSSA MODE OF ACTION GROUP NUMBER1: 14
  COMMENTS: For use around conifer or selected deciduous trees grown in the field. Oxyfluorfen sprays are effective in dormant or hardened conifers where groundsel, malva, purslane, or mustards are a problem. Oxyfluorfen will control these young plants in a few days as well as provide residual broadleaf control. Oxyfluorfen cannot be safely sprayed over most deciduous plants and is registered for use only around conifers. Safest to the conifers when applied as granules. Weak on horseweed, common chickweed, and grasses. In soil, oxyfluorfen is effective with frequent irrigation. If treated soil is cultivated, weed control is reduced.
 
I. ISOXABEN
  (Gallery) 12
  WSSA MODE OF ACTION GROUP NUMBER1: 21
  COMMENTS: Excellent for broadleaf weed control. Does not control annual grasses, therefore often it is mixed with oryzalin or other grass herbicides. Some broadleaf weed species can be controlled for up to 18 months with the labeled usage rates. Because of this long residual, the application schedule may need to be altered to accommodate this longer weed control period. Safe to a wide range of woody ornamentals. Isoxaben does not effectively control primrose, mallow, sida, and related species. Susceptible nursery crops are lilac, Euonymus alatus compacta, the mints, legumes, mustards, and members of the figwort family. Does not control willowherbs.
 
J. DICHLOBENIL
  (Casoron) 12
  WSSA MODE OF ACTION GROUP NUMBER1: 20
  COMMENTS: Labeled for use in either established or young nursery plants. A dormant season application of dichlobenil can control many seed-propagated perennial broadleaf weeds and provide residual control through early summer. The drawbacks include the limited number of ornamental species over which it may safely be used; consult the label very carefully. It can be mechanically incorporated in the top 2–3 inches to effectively control many established perennial as well as annual weeds. Good for Equisetum and mugwort control.
 
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: Provides excellent broad-spectrum control of annual broadleaf and grass weeds. Can apply after a cultivation to reduce subsequent germination. Water in after application. Residual control about 3 months.
 
B. OXYFLUORFEN/PENDIMETHALIN
  (OH II) 24
  WSSA MODE OF ACTION GROUP NUMBERS1: 14/3
  COMMENTS: One of the standards in the industry. Provides excellent broad-spectrum control of annual broadleaf and grassy weeds. Should be watered in immediately after application. Slightly less root pruning than the oryzalin/oxyfluorfen formulation (Rout). Residual control about 3 months.
 
C. ISOXABEN/TRIFLURALIN
  (Snapshot) 2.5 TG 12
  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.
 
D. OXYFLUORFEN/OXADIAZON
  (Regal O-O) 24
  WSSA MODE OF ACTION GROUP NUMBERS1: 14/14
  COMMENTS: Gives broad-spectrum control of grasses and broadleaf weeds. Soil should be thoroughly settled after cultivation and rainfall/irrigation because the product forms a surface barrier that controls seedlings as they germinate and grow through the herbicides. Cultivation after treatment destroys the control.
 
E. ISOXABEN/OXYFLUORFEN/TRIFLURALIN
  (Showcase) 24
  WSSA MODE OF ACTION GROUP NUMBERS1: 21/14/3
  COMMENTS: Similar to Snapshot but broader-spectrum control of annual broadleaf and grass weeds. Do not apply to newly transplanted ornamentals. Do not apply Showcase to wet foliage or plants where the whorls or leaves can catch granules. Longer residule.
 
POSTEMERGENT HERBICIDES
Selective (broadleaves)
A OXYFLUORFEN
  (Goal) 24
  WSSA MODE OF ACTION GROUP NUMBER1: 14
  COMMENTS: See label for tree crops for which this material is registered. Postemergent applications control certain annual broadleaf weeds. Effective only on certain young seedling weeds, especially malva; 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 are tolerant after about 5 weeks of new growth. Hemlocks, Taxus, arborvitae, junipers, Monterey pine, white pine, and Douglas fir are exceptions in that the new growth is normally not affected by oxyfluorfen. Dormant applications do not cause injury.
 
Selective (grasses)
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. Combines very well with oxyfluorfen as long as the stage of growth of the ornamental plants is tolerant of oxyfluorfen. Restricted entry interval for Fusilade is 12 hours and 4 hours for Ornamec.
 
C. CLETHODIM
  (Envoy) 24
  WSSA MODE OF ACTION GROUP NUMBER1: 1
  COMMENTS: Controls most annual and perennial grasses but not broadleaves. Effective on annual bluegrass.
 
D. SETHOXYDIM
  (Poast) 12
  WSSA MODE OF ACTION GROUP NUMBER1: 1
  COMMENTS: Controls most annual grasses, except annual bluegrass. Safe to use over most ornamentals except at flowering stage (see label).
 
Nonselective
A. GLYPHOSATE
  (Roundup Pro, Touchdown) see comments
  WSSA MODE OF ACTION GROUP NUMBER1: 9
  COMMENTS: A systemic herbicide that translocates to the roots and growing point of the plant and kills the entire plant. Effective on both annual and perennial weeds. Avoid applications where spray or drift may contact leaves of ornamentals or there may be a residual effect that might not be evident until the next season: strapped shaped leaves, stunted growth, sometimes dead shoot tips. Activity is increased in low water volumes. Greater activity is obtained at 20 gal solution/acre, for example, than at 50 gal/acre. Use alone or combined with a preemergent herbicide. Use a shielded sprayer to reduce chance of drift. Do not use in over-the-top applications. Restricted entry interval for Roundup Pro is 4 hours and 12 hours for Touchdown.
 
B. GLUFOSINATE
  (Finale) 12
  WSSA MODE OF ACTION GROUP NUMBER1: 10
  COMMENTS: Contact herbicide with a limited amount of systemic activity; kills annual weeds but only burns off the tops of perennials. Can be widely used in field-grown ornamentals.
 
C. PELARGONIC ACID
  (Scythe) 12
  WSSA MODE OF ACTION GROUP NUMBER1: 27
  COMMENTS: Labeled for use in field-grown ornamentals. Controls young annual weeds with 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 tops of perennials. Very fast acting (minutes).
 
D. PARAQUAT*
  (Gramoxone Inteon) 12
  WSSA MODE OF ACTION GROUP NUMBER1: 22
  COMMENTS: For use in field-grown ornamental trees. Kills annual weeds but only burns tops off perennials. Controls young annual weeds with contact activity only and affects only green tissue.
 
* Permit required from country 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

Top of page


Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2014 The Regents of the University of California. All rights reserved.

For noncommercial purposes only, any Web site may link directly to this page. FOR ALL OTHER USES or more information, read Legal Notices. Unfortunately, we cannot provide individual solutions to specific pest problems. See our Home page, or in the U.S., contact your local Cooperative Extension office for assistance.

Agriculture and Natural Resources, University of California

Accessibility   /PMG/r280700711.html revised: April 25, 2014. Contact webmaster.