How to Manage Pests

Floriculture and Ornamental Nurseries

Treatment for Field-grown Flowers

(Reviewed 7/00, updated 7/00)

Herbicide

(commercial name)

PREEMERGENT HERBICIDES

A.

ORYZALIN

(Surflan)

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)

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

(Factor, Barricade)

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, Pre-M, Corral 2.68G)

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. Available as a water dispersible granule, which is safer than the old EC formulation. Though it is a root inhibitor, it is less injurious to roots than oryzalin or prodiamine.

E.

NAPROPAMIDE

(Devrinol)

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)

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)

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

A.

ORYZALIN/OXYFLUORFEN

(Rout)

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)

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.

B.

PELARGONIC ACID

(Scythe)

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 Extra)

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)

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

(Grass Getter)

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-BUTYL

(Fusilade II, Ornamec)

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.

C.

CLETHODIM

(Envoy)

COMMENTS: Controls most annual grasses, including annual bluegrass. Safe to use over most ornamentals.

*

Permit required from county agricultural commissioner for purchase or use.