Walnut

Pest Management Guidelines


Herbicide Treatment Table

(Reviewed 12/07, updated 4/09)

In this Guideline: More about weeds in walnut:

Common name
(trade name)
Amount/Acre R.E.I.+
(hours)
P.H.I.+
(days)

  Calculate impact of pesticide on air quality
When choosing an herbicide, consider information relating to environmental impact Not all registered pesticides are listed. Always read label of product being used.
PREPLANT
Before weeds emerge
A. TRIFLURALIN 0.5–1 lb a.i. 12 0
  (Treflan, Trilin)    
  WSSA MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Broadcast preplant incorporated. Plant tree roots below treated soil. Do not place treated soil near roots during planting. Controls many annuals, and is helpful on perennial weeds. Residual period: 2–12 months.
   
PREPLANT
After weeds emerge
A. GLYPHOSATE 1–4 lb a.i. see label 3
  (Roundup)    
  WSSA MODE OF ACTION GROUP NUMBER1: 9
  COMMENTS: A number of glyphosate-resistant weeds have been confirmed in California. Tank mix glyphosate with other products that have a different mode of action Group number to reduce potential for development of weed resistance. 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. 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. Apply to young annuals or vigorously growing perennials in flowering stage. Some perennials require the 4 lb/acre rate for control. May be used on young weeds in strip followed by planting into the dead weeds. New weeds usually do not establish for a month or more, due to the no-till effect. Do not use more than 9.77 lb/year.
   
POSTPLANT
Before weeds emerge
A. TRIFLURALIN 1–2 lb a.i. 12 0
  (Treflan HFP, etc.)    
  WSSA MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: For use on nonbearing and bearing trees. Apply as a directed spray and mechanically incorporate, taking care not to injure the tree. Residual period: 2–12 months.
   
B. ORYZALIN 2–6 lb a.i. 24 0
  (Surflan A.S.)    
  WSSA MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: For use on nonbearing and bearing English walnut trees. Apply to the soil surface in 20–60 gal water/acre. If rain does not occur within 21 days, sprinkle irrigate with 0.5 to 2.0 inches of water. May be combined with a postemergent herbicide if weeds are present. The higher rates give the longest soil residual. Usually used at 4.0 lb a.i./acre. Residual period: 4–10 months.
   
C. NAPROPAMIDE 4 lb a.i. 12 35
  (Devrinol 50DF)    
  WSSA MODE OF ACTION GROUP NUMBER1: 15
  COMMENTS: For use on nonbearing and bearing dormant trees. Use being dropped from the label. Read label carefully to be sure that the crop is listed on the label of the product used. Apply to the soil surface in 20–50 gal water/acre. Must be incorporated within 7 days of application or sprinkler irrigated. Needs to be combined with a postemergent herbicide if weeds have emerged. Residual period: 4–10 months.
   
D. OXYFLUORFEN 1–2 lb a.i. 24 0
  (Goal 2XL)    
  WSSA MODE OF ACTION GROUP NUMBER1: 14
  COMMENTS: For use on nonbearing and bearing dormant trees only. Apply in 20–60 gal water/acre on firm soil. Must not be mechanically disturbed or poor weed control will result. Often combined with oryzalin. Check label for use period. Residual period: 4–10 months.
 
E. PENDIMETHALIN 2–3.96 lb a.i. 24 365
  (Prowl 3.3EC)    
  WSSA MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: For use on dormant nonbearing English walnut trees only. Apply in 20 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 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.
   
F. DIURON Label rates 12 0
  (Karmex DF)    
  WSSA MODE OF ACTION GROUP NUMBER1: 7
  COMMENTS: For use on English walnut trees only. Direct 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. Do not apply more than 3 lb a.i./season. Diuron is sometimes combined with other preemergent herbicides to broaden spectrum of weeds controlled. These combination treatments frequently use lower rates of diuron. Do not apply to trees with trunks less than 1.5 inch in diameter. NOTE: Pay special attention to soil texture/rate adjustments. Do not use on soils with less than 1% organic matter. Considered to be a ground water contaminant and requires a use permit within groundwater protection areas. Residual period: 8–12 months.
       
G. SIMAZINE 2–3.96 lb a.i. 12 0
  (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 preemergent 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 groundwater protection areas. Residual period: 8–12 months.
       
H. NORFLURAZON 3–3.93 lb a.i. 12 60
  (Solicam DF)    
  WSSA MODE OF ACTION GROUP NUMBER1: 12
  COMMENTS: Apply to soil as a directed spray from fall to early spring under trees established for at least 2 years. Do not use on coarse-textured soils or south of Monterey, Kings, and Tulare counties. Do not use on sandy loam soils after budbreak. Apply in 20–100 gal water/acre. Considered to be a ground water contaminant and requires a use permit within groundwater protection areas.
       
POSTPLANT
After weeds emerge (postemergent)
A. GLYPHOSATE 1–4 lb a.i. see label 3
  (Roundup)
  WSSA MODE OF ACTION GROUP NUMBER1: 9
  COMMENTS: A number of glyphosate-resistant weeds have been confirmed in California. Tank mix glyphosate with other products that have a different mode of action Group number to reduce potential for development of weed resistance. 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. 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 for control. Avoid drift onto green bark or foliage or injury will result.
       
B. PARAQUAT* 0.65–1 lb a.i. 12 0
  (Gramoxone Inteon)    
  WSSA MODE OF ACTION GROUP NUMBER1: 22
  COMMENTS: Apply in 20–60 gal water/acre to young weeds. Use 0.5% nonionic surfactant. Repeat treatment as new growth occurs. Avoid drift onto trees or injury will result.
   
C. OXYFLUORFEN 0.5–1 lb a.i. 24 0
  (Goal 2XL)    
  WSSA MODE OF ACTION GROUP NUMBER1: 14
  COMMENTS: Dormant application to young (4-leaf-stage) weeds. May be combined with other postemergent herbicides for specific weeds. Check label for use period.
   
D. FLUAZIFOP-P-BUTYL 0.25–0.375 lb a.i. 12 365
  (Fusilade DX)    
  WSSA MODE OF ACTION GROUP NUMBER1: 1
  COMMENTS: For control of annual and perennial grasses in nonbearing trees. Do not apply to trees within 1 year of harvest. Apply 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 are required for johnsongrass and bermudagrass. Residual period: less than 1 month.
   
E. SETHOXYDIM 0.28–0.46 lb a.i. 12 15
  (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 of nonphytotoxic oil to the spray solution. Residual period: less than 1 month.
       
F. 2,4-D* 1.4 lb a.i. 48 60
  (Orchard Master)    
  WSSA MODE OF ACTION GROUP NUMBER1: 4
  COMMENTS: For use on established trees 1 year or older. Apply as a directed spray to weeds, using low pressure flooding nozzles between the tree rows. Do not allow drift onto the trees or injury may result. No more than 2 applications allowed during the growing season. Residual period: 4–6 weeks.
 
POSTPLANT
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.
A. GLYPHOSATE 0.5–1 lb a.i. 4 3
  (Roundup)    
  WSSA MODE OF ACTION GROUP NUMBER1: 9
  . . . PLUS . . .    
  OXYFLUORFEN 0.1–1 lb a.i. 24 0
  (Goal 2XL)    
  WSSA MODE OF ACTION GROUP NUMBER1: 14
  COMMENTS: For broad-spectrum control of emerged weeds. Apply in 3–10 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.
   
B. GLYPHOSATE 1 lb a.i. 4 3
  (Roundup)    
  WSSA MODE OF ACTION GROUP NUMBER1: 9
  . . . PLUS . . .    
  ORYZALIN 4 lb a.i. 24 0
  (Surflan A.S.)    
  WSSA MODE OF ACTION GROUP NUMBER1: 3
  . . . or . . .    
  NAPROPAMIDE 4 lb a.i. 12 35
  (Devrinol) 50DF    
  WSSA MODE OF ACTION GROUP NUMBER1: 15
  COMMENTS: Use being dropped from the Devrinol label. Read label carefully to be sure that the crop is listed on the label of the product used. Combines post- and preemergent 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.
   
C. PARAQUAT* 0.5 lb a.i. 12 0
  (Gramoxone Inteon)    
  WSSA MODE OF ACTION GROUP NUMBER1: 22
  . . . PLUS . . .    
  OXYFLUORFEN 0.5–1 lb a.i. 24 0
  (Goal 2XL)    
  WSSA MODE OF ACTION GROUP NUMBER1: 14
  COMMENTS: Broad-spectrum postemergent control. Avoid drift and follow directions for application period of oxyflurofen.
   
D. ORYZALIN 4 lb a.i. 24 0
  (Surflan A.S.)    
  WSSA MODE OF ACTION GROUP NUMBER1: 3
  . . . PLUS . . .    
  OXYFLUORFEN 1 lb a.i. 24 0
  (Goal 2XL)    
  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.
   
E. SIMAZINE 1–2 lb a.i. 12 0
  (Princep Caliber 90)    
  WSSA MODE OF ACTION GROUP NUMBER1: 5
  . . . PLUS . . .    
  DIURON 1–2 lb a.i. 12 0
  (Karmex DF)    
  WSSA MODE OF ACTION GROUP NUMBER1: 7
  . . . PLUS . . .    
  GLYPHOSATE 1 lb a.i. 4 3
  (Roundup)    
  WSSA MODE OF ACTION GROUP NUMBER1: 9
  COMMENTS: For use on medium to heavy soils. This combination is effective on a broad range of weed species. Use lower rates on light soils and high rates on heavy, fine textured soils. Simazine is considered to be a ground water contaminant and requires a use permit within groundwater protection areas. Residual period: 8–12 months.
   
F. GLYPHOSATE    
  (Roundup) 0.5 lb a.i. 4 3
  WSSA MODE OF ACTION GROUP NUMBER1: 9
  . . . PLUS . . .    
  2,4-D* 0.5 lb a.i. 48 60
  (Orchard Master)    
  WSSA MODE OF ACTION GROUP NUMBER1: 4
  . . . PLUS . . .    
  SURFACTANT 0.5–1%  
  COMMENTS: Combined to give broad-spectrum control. Apply postemergence to young, growing weeds. Avoid drift or contact with leaves.
       
ORGANIC ORCHARDS
A. CLOVE OIL Label rates until dry 0
  (Matran EC)    
  COMMENTS: Manufactured by EcoSmart.
   
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. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of these two intervals is the minimum time that must elapse before harvest may occur.
* Permit required from county agricultural commissioner for purchase or use.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Walnut
UC ANR Publication 3471

Weeds
  • A. Shrestha, UC IPM Program/Kearney Agricultural Center, Parlier
  • R. B. Elkins, UC Cooperative Extension, Lake County
  • J. K. Hasey, UC Cooperative Extension, Sutter/Yuba Counties
  • K. K. Anderson, UC Cooperative Extension, Stanislaus County
Acknowledgment for contributions to Weeds:
  • C. L. Elmore, Weed Science/Plant Sciences, UC Davis
  • G. S. Sibbett, UC Cooperative Extension, Tulare County
  • W. O. Reil, UC Cooperative Extension, Yolo County
  • T. S. Prather, Plant, Soil, and Entomological Sciences, University of Idaho, Moscow, ID
  • J. J. Stapleton, UC IPM Program/Kearney Agricultural Center, Parlier
  • J. A. Grant, UC Cooperative Extension, San Joaquin County

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