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How to Manage Pests

UC Pest Management Guidelines


Field-grown bedding plants in full bloom.

Floriculture and Ornamental Nurseries

Treatment for Container Nurseries

(Reviewed 3/09, updated 6/10)

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.
Note: Not all ornamentals will tolerate each herbicide. Check the label for species selectivity.
 
PREEMERGENT HERBICIDES
A. ORYZALIN
  (Surflan, etc.) 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 around many woody and herbaceous 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 pines, Taxus, arborvitae, and junipers are more tolerant. Stems of Monterey pines may exhibit some swelling. Oryzalin is a strong root inhibitor. Most broadleaf ornamentals are very tolerant to oryzalin if the herbicide is not in the root zone. Often used in combination with other herbicides to widen weed spectrum controlled.
  Even when applied at rates of 4 lb (4.4 kg/ha) 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. Can control spotted spurge and oxalis from seed for about 4 months. Re-treatments have been required for full-season (1-year) control. Re-treat at about 3- to 4-month intervals and supplement with some hand-weeding for best control of most weeds.
 
B. TRIFLURALIN
  (Treflan, etc.) 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, or covered with a mulch, very soon after application. Inhibits root growth. Often mixed with other herbicides (isoxaben or benefin) to widen weed spectrum controlled.
 
C. PRODIAMINE
  (Barricade, Endurance) 12
  MODE OF ACTION: Unknown.
  COMMENTS: Stable on the soil surface. Does not provide as long weed control as oryzalin at the maximum label rates for both. Has been less effective for spurge and groundsel suppression than some other dinitroaniline herbicides. Inhibits root growth. Low water solubility and does not move deeply in the soil.
 
D. PENDIMETHALIN
  (Pendulum, etc.) 24
  WSSA MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Gives excellent grass control and controls many broadleaf weeds. Weed spectrum controlled is similar to that of oryzalin. Often combined with an additional herbicide material to widen spectrum of weeds controlled. Controls oxalis and spotted spurge. Available as a water dispersible granule and a newer formulation (AquaCap) has no odor and less persistent orange color. Both are safe over the top of many nursery plants. 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. 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. It is 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 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.
 
F. 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 a sprinkler irrigation following application. Oxadiazon is a shoot-girdling herbicide. Used during the growing season from spring until fall. Granular oxadiazon is safe on most woody plants. The wettable powder formulation is generally not used in nursery stock. In containers, granular oxadiazon plus napropamide is a good combination, with a broad range of safety in woody plants. Oxadiazon plus napropamide often has an improved margin of safety over Rout or OHII, especially in young, actively growing plants. 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 pearlwort, chickweed, and horseweed. Re-treatments are required at about 3- to 4-month intervals to maintain control throughout the season. 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, however, 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.
 
G. OXYFLUORFEN
  (Goal XL) 24
  WSSA MODE OF ACTION GROUP NUMBER1: 14
  COMMENTS: For use around conifers in container production. An excellent place for oxyfluorfen sprays is in dormant or hardened conifers where groundsel, malva, purslane, or mustards are found. Controls these weeds in a few days and provides 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. Oxyfluorfen acts by girdling the young stem of seedlings; thus in soil, oxyfluorfen is most effective with frequent irrigation. If treated soil is cultivated, weed control is reduced.
 
H. ISOXABEN
  (Gallery) 12
  WSSA MODE OF ACTION GROUP NUMBER1: 21
  COMMENTS: Excellent material for broadleaf weed control. The major weakness is poor 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. It is safe to a wide range of woody ornamentals. Isoxaben does not effectively control mallow or willowherb and related species. Disadvantages associated with using isoxaben are the cost and potential crop injury. Susceptible nursery crops are lilac, Euonymus alatus compacta, mints, legumes, snapdragon, mustards, and members of the figwort family. Some herbaceous ornamentals such as Veronica and Digitalis may be killed by postplant, preemergent applications of isoxaben.
 
I. FLUMIOXAZIN
  Broadstar (granular), Sureguard (sprayable) 12
  WSSA MODE OF ACTION GROUP NUMBER1: 14
  COMMENTS: Avoid contact with young plants or foliage. Wash foliage as soon as possible after application. Can cause stem dieback or leaf burn on sensitive plants. Has some postemergent activity. Provides good liverwort control. Helps provide preemergent control of annual grasses, chickweed, horseweed, hairy fleabane, and other annual broadleaves. Test on a small number of plants before using widely.
 
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: One of the standards in the container industry. 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.
 
B. OXYFLUORFEN/PENDIMETHALIN
  (OH II) 24
  WSSA MODE OF ACTION GROUP NUMBERS1: 14/3
  COMMENTS: One of the standards in the container industry. Provides excellent broad-spectrum control of annual broadleaf and grassy weeds. Should be watered-in immediately after application. Residual control is 3–4 months.
 
C. ISOXABEN/TRIFLURALIN
  (Snapshot TG) 12
  WSSA MODE OF ACTION GROUP NUMBERS1: 21/3
  COMMENTS: Gives broad-spectrum control of annual broadleaf and grass weeds.
 
D. OXYFLUORFEN/OXADIAZON
  (Regal O-O) 24
  WSSA MODE OF ACTION GROUP NUMBERS1: 14/14
  COMMENTS: Gives broad-spectrum of control. Plants with leaf bases that hold granules can be injured, but formulation is such that most of the material falls through the canopy to the soil surface.
 
E. OXADIAZON/PRODIAMINE
  (Regalstar II) 12
  WSSA MODE OF ACTION GROUP NUMBERS1: 14/Unknown.
  COMMENTS: Gives broad-spectrum grass and broadleaf control. Injury may occur if material is applied to wet foliage. Formulation is similar to Regal O-O.
 
F. DIMETHENAMID-P/PENDIMETHALINE
  (Freehand) 1.75G 24
  WSSA MODE OF ACTION GROUP NUMBERS1: 15/3
  COMMENTS: Controls many common nursery weeds such as eclipta, spurges, willowherbs, and oxalis. Can be applied very soon after potting. Provides preemergence control or suppression of yellow nutsedge.
 
G. 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
Nonselective
A. GLYPHOSATE
  (Roundup Pro) 4
  WSSA MODE OF ACTION GROUP NUMBER1: 9
  COMMENTS: Labeled for use around container-grown ornamentals. A systemic herbicide that translocates to the roots and growing point of plant 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 preemergent herbicide. Often takes 7 or more days after application for complete control. Avoid drift.
 
B. PELARGONIC ACID
  (Scythe) 12
  WSSA MODE OF ACTION GROUP NUMBER1: 27
  COMMENTS: Labeled for use around container-grown ornamentals. Works by contact activity only (does not move in plant) and affects only green tissue. Kills annual weeds (good control of young annuals weeds), but only burns off the tops of perennials. Must be applied at high rates in high volumes of water. Very rapid (minutes in high sunlight) activity. Growers have experimented with this product as a semi-selective herbicide. In some cases lower effective rates of this herbicide might be applied over crops with only minor injury, while completely eliminating susceptible annual weeds in the container. In some cases, the product has been directed towards susceptible annual weeds in the container if the crop plant has a leafless, woody base, or the plant is shielded from the spray.
 
C. PARAQUAT*
  (Gramoxone Inteon) 24
  WSSA MODE OF ACTION GROUP NUMBER1: 22
  COMMENTS: Can be used around the perimeters of nursery. Controls young annual weeds; contact activity only; affects only green tissue.
 
D. DIQUAT
  (Reward) 24
  WSSA MODE OF ACTION GROUP NUMBER1: 22
  COMMENTS: Labeled for use around container-grown ornamentals. Kills annuals weeds, but only burns off the tops of perennials. Control of young annual weeds; contact activity only; affects only green tissue. Good for weed control in winter.
 
Selective (broadleaves)
A. OXYFLUORFEN
  (Goal) 24
  WSSA MODE OF ACTION GROUP NUMBER1: 14
  COMMENTS: Registered for use around conifers only. Postemergent 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. 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. 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 products; consult the label carefully. Combines very well with oxyfluorfen as long as the stage of growth of the ornamental plants is tolerant to oxyfluorfen. Requires a surfactant. Restricted entry interval for Fusilade is 12 hours; for Ornamec it is 4 hours.
 
B. CLETHODIM
  (Envoy) 24
  WSSA MODE OF ACTION GROUP NUMBER1: 1
  COMMENTS: Controls most annual grasses, including annual bluegrass. Safe to use over most ornamentals except at flowering stage (see label).
 
* 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

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