UC IPM: Information about Herbicides in Pear

UC Pest Management Guidelines

Common name

Amount/Acre

R.E.I.+

P.H.I.+

(trade name)

(hours)

(days)

When choosing a pesticide, consider information relating to environmental impact.

PREPLANT

Preemergent (before weeds germinate)

TRIFLURALIN

0.5–1 lb a.i.

(Treflan)

WSSA MODE OF ACTION GROUP NUMBER¹: 3

COMMENTS: Broadcast preplant in 5 to 40 gallons of water per acre. Trifluralin must be incorporated immediately after application to avoid loss of activity. Plant tree roots below treated soil. Do not place treated soil near roots during planting. Controls many annuals and is helpful in suppressing perennial weeds. Residual period: 2–12 months.

Postemergent (after weeds emerge)

GLYPHOSATE

1–4 lb a.i.

(Roundup WeatherMax, etc.)

. . . or . . .

(Touchdown)

1–3.75 lb a.i.

WSSA MODE OF ACTION GROUP NUMBER¹: 9

COMMENTS: Apply with a controlled applicator or with low-pressure flat fan nozzles. For annual weed control, use 1 lb/acre in 3–10 gal water. Ammonium sulfate can also be added (1 to 2% by weight or 8.5 to 17 lbs per 100 gallon of water) to the spray solution to significantly improve control in areas with hard water. It is important to add the ammonium sulfate to the water before adding the herbicide. Apply to young annuals or vigorously growing perennials in flowering stage. Some perennials require the 4 lb/acre of glyphosate rate for control. May be used on young weeds in the planting row followed by planting into the dead weeds. As a result of the no-till effect, new weeds usually do not establish for a month or more. Do not use more than 10.6 lb/year.

NEWLY PLANTED ORCHARDS (nonbearing trees)

Preemergent

ISOXABEN

0.5–0.9975 lb a.i.

365

(Gallery T&V)

WSSA MODE OF ACTION GROUP NUMBER¹: 21

COMMENTS: Wait until soil has settled around newly planted trees before applying. Controls broadleaf weeds only before they have germinated; will not control emerged weeds. If weeds are emerged, lightly cultivate or add a postemergent herbicide. Requires incorporation for activation, either by light cultivation (1 to 2 inches) or rainfall (minimum of 0.5 inches) within 21 days after application. Sprinkler or flood irrigation can also be used for incorporation. Apply in at least 10 gal of water/acre.

TRIFLURALIN

1–2 lb a.i.

(Treflan)

WSSA MODE OF ACTION GROUP NUMBER¹: 3

COMMENTS: Preemergent selective herbicide for annual grasses. Apply prebloom by ground and mechanically incorporate, taking care not to injure the trees with the incorporation. Must be incorporated immediately after application to avoid loss of activity. Used on new plantings or established orchards as a strip treatment. Suppresses bermudagrass, johnsongrass, and dallisgrass rhizomes. Only one application per year. Residual period: 2–12 months.

ORYZALIN

2–6 lb a.i.

(Surflan, Oryzalin 4 A.S. etc.)

WSSA MODE OF ACTION GROUP NUMBER¹: 3

COMMENTS: Preemergent selective herbicide for annual grasses. Apply to the soil surface in 20–40 gal water/acre. If rain does not occur within 21 days, sprinkle irrigate with 0.5–2 inches of water. May be combined with a postemergent herbicide if weeds are present. Most effect on annual grasses and numerous broadleaf annuals. Very safe for young or newly planted trees and on sandy or sandy loam soils. Used to maintain control in strips down the row. The higher rates give the longest soil residual. Usually used at 4 lb a.i./acre. Residual period: 4–10 months.

NAPROPAMIDE

4 lb a.i.

(Devrinol 50DF)

WSSA MODE OF ACTION GROUP NUMBER¹: 15

COMMENTS: Apply to the soil surface in 20–60 gal water/acre. Use only once per season. Must be incorporated mechanically or with sprinkler irrigation or rainfall within 21 days of application between November and February or within 24 hours the remainder of the year. Effective on annual grasses and several annual broadleaves. Effective in maintaining weed-free strips down the row. Needs to be combined with a postemergent herbicide if weeds have emerged. Residual period: 4–10 months.

PENDIMETHALIN

2–3.96 lb a.i.

365

(Prowl 3.3EC etc.)

WSSA MODE OF ACTION GROUP NUMBER¹: 3

COMMENTS: For use on dormant nonbearing trees only. Apply in 10 or more gal water/acre to soil under trees. Do not apply on newly planted trees unless soil is firm and there are no cracks in soil around base of trees. Best control is achieved when irrigation or rainfall occurs within 7 days. Will not control emerged weeds. Residual period: 4–10 months

PRONAMIDE*

1–4 lb a.i.

(Kerb)

WSSA MODE OF ACTION GROUP NUMBER¹: 3

COMMENTS: Do not apply to trees less than 1 year old. Selective herbicide for control of winter annual and perennial grasses. Apply in fall after fruit harvest. Apply in 40-50 gal water/acre to the soil at the base of the trees. Must be applied before weed emergence because it will not control emerged weeds. Rainfall or irrigation is essential after application for effective weed control. Residual period: 4-8 months.

DICHLOBENIL

4–6 lb a.i.

(Casoron) 4G

WSSA MODE OF ACTION GROUP NUMBER¹: 20

COMMENTS: Apply to soil under trees. Do not apply on young trees until 1 month after planting. Do not apply within 1 month of harvest. For best results, incorporate and follow with 1/2 to 1 inch of water or an immediate shallow incorporation. Dichlobenil can be very effective in controlling perennial weeds around sprinkler heads. Residual period: 4–6 months.

Postemergent

CLETHODIM

0.095-0.12484 lb a.i.

365

(Prism)

WSSA MODE OF ACTION GROUP NUMBER¹: 1

COMMENTS: For use on nonbearing trees only. Apply to young perennial grasses. Repeat applications will be required for the control of perennial grasses. Apply in 5 to 40 gal water/acre. Add 0.25% volume per volume nonionic surfactant to the spray solution. Spray pressure should be between 30 and 60 PSI, with higher pressures used when weed density is high. Do not apply a broadleaf herbicide within one day following application or reduced grass control may occur. Residual period: less than one month.

OXYFLUORFEN

1–1.5 lb a.i.

(Goal 2XL)

WSSA MODE OF ACTION GROUP NUMBER¹: 14

COMMENTS: Nonbearing and bearing trees. Apply in 20–60 gal water/acre on firm soil. Must not be mechanically disturbed or poor weed control will result. Often is combined with oryzalin. Check label for use period. Residual period: 2–6 months. Do not use after February 15.

FLUMIOXAZIN

0.188-0.376 lb a.i.

365

(Chateau SW)

WSSA MODE OF ACTION GROUP NUMBER¹: 14

COMMENTS: For use on dormant nonbearing trees only. Apply in 10 or more gal water/acre to soil under trees when completely dormant. Do not apply on newly planted trees unless soil is firm and there are no cracks in soil around base of trees. Best control is achieved when irrigation or rainfall occurs within 21 days. Can be mixed with other pre- or postemergent herbicides. It will not provide adequate control of emerged weeds, unless mixed with a postemergent herbicide. Use allowed under a supplemental label. Residual period: 3–6 months

SETHOXYDIM

0.19–0.4675 lb a.i.

(Poast)

WSSA MODE OF ACTION GROUP NUMBER¹: 1

COMMENTS: Apply to young perennial grasses. Repeat applications will be required for the control of perennial grasses. Add 2 pt/acre of a nonphytotoxic crop oil concentrate to the spray solution. Residual period: less than one month.

CARFENTRAZONE

0.008–0.03 lb a.i.

(Shark)

WSSA MODE OF ACTION GROUP NUMBER¹: 14

COMMENTS: A postemergent, contact herbicide used for quick top kill of most broadleaf weed species. Can be applied anytime during the season, but if fruit are present, it should either be avoided or applied with extreme care to avoid drift. It can also be used for sucker control. Apply in a minimum of 20 gal water/acre to weeds less than 6 inches tall. Repeat treatments as new growth occurs, but they must be at least 14 days apart. Do not use more than 0.124 lb a.i./acre/season. Use 0.25% volume per volume nonionic surfactant, 1.0% volume per volume of a crop oil concentrate, or a silicone or MSO surfactant.

FLUAZIFOP-P-BUTYL

0.25–0.375 lb a.i.

365

(Fusilade DX)

WSSA MODE OF ACTION GROUP NUMBER¹: 1

COMMENTS: For use on non-bearing trees only. Apply in 20–40 gal water/acre and add 0.5% nonionic surfactant. Do not apply to grass that is stressed or poor control may result. Repeat applications may be required for johnsongrass and bermudagrass. Residual period: less than 1 month.

2,4–D*

0.95-1.425 lb a.i.

(Orchard Master etc.)

WSSA MODE OF ACTION GROUP NUMBER¹: 4

COMMENTS: For use on established trees one year or older. Effective on most broadleaf annual weeds. Provides partial control of field bindweed. Apply as a directed spray to weeds, using low-pressure, flooding nozzles between the tree rows. Best results are obtained when applied a few days after an irrigation. Do not allow drift onto the trees or injury may result. No more than two applications allowed during the growing season. Residual period: 4–6 weeks.

ESTABLISHED ORCHARDS

Preemergent

ORYZALIN

2–6 lb a.i.

(Surflan, Oryzalin 4 A.S. etc.)

WSSA MODE OF ACTION GROUP NUMBER¹: 3

COMMENTS: Apply to the soil surface in 20–40 gal water/acre. If rain does not occur within 21 days, sprinkle irrigate with 0.5–2 inches of water. Most effect on annual grasses and numerous broadleaf annuals. Very safe for sandy or sandy loam soils. Used to maintain control in strips down the row. May be combined with a postemergent herbicide if weeds are present. The higher rates give the longest soil residual. Usually used at 4 lb a.i./acre. Residual period: 4–10 months.

NAPROPAMIDE

4 lb a.i.

(Devrinol 50DF)

WSSA MODE OF ACTION GROUP NUMBER¹: 15

COMMENTS: Apply to the soil surface in 20–60 gal water/acre. Use only once per season. Must be incorporated either mechanically or with sprinkler irrigation or rainfall, within 21 days of application between November and February, or within 24 hours the remainder of the year. Effective on annual grasses and several annual broadleaves. Effective in maintaining weed-free strips down the row. Needs to be combined with a postemergent herbicide if weeds have emerged. Residual period: 4–10 months.

NORFLURAZON

1.97–3.93 lb a.i.

(Solicam DF)

WSSA MODE OF ACTION GROUP NUMBER¹: 12

COMMENTS: Similar to oryzalin but is effective on more annual broadleaf and grass species. Can suppress yellow nutsedge or bermudagrass when used year after year. Apply to soil as a directed spray from fall to early spring under trees established for at least 2 years. If no rainfall occurs within 4 weeks, incorporate with sprinkler or flood irrigation. Remove existing weeds with cultivation or a postemergent herbicide, because it has no postemergent activity. Avoid higher rates on sandy or gravelly soils to prevent injury to trees. Considered to be a ground water contaminant and requires a use permit within Ground Water Protection Areas. Do not use in the Coachella Valley. Apply in 20–100 gal water/acre. Residual period: 6–12 months.

OXYFLUORFEN

0.5–1.5 lb a.i.

(Goal 2 XL etc.)

WSSA MODE OF ACTION GROUP NUMBER¹: 14

COMMENTS: For use on dormant trees only. Apply following harvest up to February 15 (February 1 in the Coachella Valley). Apply by ground one time per season in 40–100 gal water/acre on firm soil. Must not be mechanically disturbed or poor weed control will result. Effective as a pre- and postemergent herbicide. Effective on little mallow (cheeseweed). Useful combined with other postemergent herbicides, such as glyphosate, or in combination with preemergent herbicides, such as oryzalin, simazine, or thiazopyr. Check label for use period. Residual period: 4–10 months.

PRONAMIDE*

1–4 lb a.i.

(Kerb)

WSSA MODE OF ACTION GROUP NUMBER¹: 3

DIURON

1.6–3.2 lb a.i.

(Karmex, Direx, Diuron)

WSSA MODE OF ACTION GROUP NUMBER¹: 7

COMMENTS: Apply to the soil under trees at least 3 years of age. A single application may be made in winter or split between fall and spring. Diuron is sometimes combined with other preemergent herbicides to broaden spectrum of weeds controlled. These combination treatments frequently use lower rates of diuron. Adjust rates according to soil texture. Do not use on soils with less than 1% organic matter. Considered to be a ground water contaminant and requires a use permit within Ground Water Protection Areas. Residual period: 8-12 months.

SIMAZINE

1–2 lb a.i.

(Princep Caliber 90)

WSSA MODE OF ACTION GROUP NUMBER¹: 5

COMMENTS: Apply to the soil under trees older than 3 years. Make only one application per year. Use the high rate for heavy soils. Simazine is frequently used in combination with other preemergence herbicides. On light soils, simazine often is used at rates of 0.5-1.0 lb a.i./acre. Do not use on gravel, sand, or loamy sand soils. If an irrigation is applied immediately after application, limit water to 0.5 inch. Considered to be a ground water contaminant and requires a use permit within Ground Water Protection Areas. Residual period: 8-12 months.

DICHLOBENIL

4–6 lb a.i.

(Casoron) 4G

WSSA MODE OF ACTION GROUP NUMBER¹: 20

Postemergent

GLYPHOSATE

1–4 lb a.i.

(Roundup WeatherMax, etc.)

. . . or . . .

(Touchdown)

1–3.75 lb a.i.

WSSA MODE OF ACTION GROUP NUMBER¹: 9

COMMENTS: Apply with controlled droplet application or with low-pressure, flat-fan nozzles. For annual weed control, use 1 lb a.i./acre in 3–10 gal water. Ammonium sulfate can also be added (1 to 2% by weight or 8.5 to 17 lbs per 100 gallon of water) to the spray solution to improve control in areas with hard water. It is important to add the ammonium sulfate to the water before adding the herbicide. For chemical mowing, consult label for exact timing and rates, depending on weed size and species. Apply to young annuals or vigorously growing perennials. Some perennials require the 4 lb a.i./acre rate of glyphosate for control. A good herbicide for perennial weeds, but doesn't eradicate field bindweed or nutsedge. Not effective on some broadleaf weeds at older stages of growth (little mallow and filaree). Avoid drift onto green bark or foliage of tree or injury will result. It is important to monitor treated areas for escaped weeds, as glyphosate resistant weeds have been observed in orchards where glyphosate has been used repeatedly for several years.

PARAQUAT*

0.625–1.0 lb a.i.

(Gramoxone Inteon)

WSSA MODE OF ACTION GROUP NUMBER¹: 22

COMMENTS: Nonselective postemergent, contact herbicide used for quick top kill of most weed species. Less effective against perennials that will regrow (bermudagrass, dallisgrass, johnsongrass and field bindweed). Most effective when used in late winter or early spring on small annual grass species in combination with preemergent herbicides. Apply in 10–60 gal water/acre to young weeds. Use 0.25% volume per volume nonionic surfactant or 1.0% volume per volume of a crop oil concentrate. Repeat treatment as new growth occurs. Do not exceed 3 applications/season.

OXYFLUORFEN

0.5–1.5 lb a.i.

(Goal 2 XL etc.)

WSSA MODE OF ACTION GROUP NUMBER¹: 14

COMMENTS: Dormant application to young (4-leaf-stage) weeds. Effective on little mallow (cheeseweed) and filaree. Useful combined with glyphosate or oryzalin. May be combined with other postemergent herbicides for specific weeds. Apply following harvest up to February 15 (February 1 in the Coachella Valley). Apply by ground one time per season in 40–100 gal water/acre on firm soil. Must not be mechanically disturbed or poor weed control will result. Effective as a pre-and postemergent herbicide. Residual period: 4–10 months.

2,4–D*

0.95-1.425 lb a.i.

(Orchard Master etc.)

WSSA MODE OF ACTION GROUP NUMBER¹: 4

SETHOXYDIM

0.19–0.4675 lb a.i.

(Poast)

WSSA MODE OF ACTION GROUP NUMBER¹: 1

CARFENTRAZONE

0.008–0.03 lb a.i.

(Shark)

WSSA MODE OF ACTION GROUP NUMBER¹: 14

Herbicide combinations

(Note: Combinations are most often used to broaden the weed control spectrum. At the rates recommended below, perennial weeds will not be controlled. Other combinations can be used depending upon the weed spectrum present in the orchard. 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.)

GLYPHOSATE

0.5–1 lb a.i.

see label

(Roundup, Touchdown, etc.)

WSSA MODE OF ACTION GROUP NUMBER¹: 9

. . . PLUS . . .

OXYFLUORFEN

0.1–1 lb a.i.

(Goal 2XL, etc.)

WSSA MODE OF ACTION GROUP NUMBER¹: 14

COMMENTS: For broad-spectrum control of emerged weeds. Apply in a minimum of 10 gal water/acre in dormant trees. Helps increase control of cheeseweed, filaree, chickweed, and grasses. Glyphosate effectiveness is increased with low-water volume and oxyfluorfen is more effective at the higher volume. Avoid drift and follow directions for application period of oxyfluorfen.

GLYPHOSATE

0.5–1 lb a.i.

see label

(Roundup, Touchdown, etc.)

WSSA MODE OF ACTION GROUP NUMBER¹: 9

. . . PLUS . . .

ORYZALIN

4 lb a.i.

(Surflan, etc.)

WSSA MODE OF ACTION GROUP NUMBER¹: 3

. . . or . . .

NAPROPAMIDE

4 lb a.i.

(Devrinol 50DF)

WSSA MODE OF ACTION GROUP NUMBER¹: 15

COMMENTS: Combines pre- and postemergent control of most annual weeds with residual up to 6 months. Combination choice depends on weed spectrum and how rapid incorporation will occur. Napropamide needs irrigation within 7 days, oryzalin within 21 days.

ORYZALIN

4 lb a.i.

(Surflan, etc.)

WSSA MODE OF ACTION GROUP NUMBER¹: 3

. . . PLUS . . .

OXYFLUORFEN

1.5 lb a.i.

(Goal 2XL, etc.)

WSSA MODE OF ACTION GROUP NUMBER¹: 14

COMMENTS: Combined to give broad-spectrum control. Apply preemergence or combined with paraquat or glyphosate if weeds have emerged. Irrigate within 21 days if rain has not occurred.

GLYPHOSATE

0.5 lb a.i.

see label

(Roundup, Touchdown, etc.)

WSSA MODE OF ACTION GROUP NUMBER¹: 9

. . . PLUS . . .

2,4–D*

0.5 lb a.i.

(Orchard Master CA, etc.)

WSSA MODE OF ACTION GROUP NUMBER¹: 4

. . . PLUS . . .

SURFACTANT

0.5–1%

N.A.

COMMENTS: Combined to give broad-spectrum control. Apply postemergence to young, growing weeds. Avoid drift or contact with leaves.

+	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. Preharvest interval (P.H.I.) is the number of days from treatment until the harvest may take place. In some cases the R.E.I. exceeds the P.H.I. The longer of these two intervals is the minimum time that must elapse before harvest may take place.
*	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.plantprotection.org/HRAC/.
N.A.	Not applicable.

UC IPM Pest Management Guidelines: Pear
UC ANR Publication 3455
Weeds
R. B. Elkins, UC Cooperative Extension, Lake Co.
W. T. Lanini, Weed Science/Plant Sciences, UC Davis
Acknowledgment for contributions to the weed section:
C. L. Elmore, Vegetable Crops/Weed Science, UC Davis
G. T. McGourty, UC Cooperative Extension, Mendocino Co.

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