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How to Manage Pests

UC Pest Management Guidelines

| More pests | More crops | About guidelines |

Field bindweed, Convolvulus arvensis.

Onion and Garlic

Herbicide Treatment Table

(Reviewed 1/07, updated 1/07)

In this Guideline: More about weeds in onion and garlic:
Common name Amount/Acre R.E.I.+ P.H.I.+
(trade name)   (hours) (days)
When choosing a herbicide, consider information relating to environmental impact.
 
PREPLANT
A. METAM SODIUM* 50–75 gal 48 —
  (various products)    
  COMMENTS: Beds must be free of large clods and the soil should be moistened by rainfall or irrigation before application. Soil temperatures should be between 40°–90°F at the 3-inch depth. Broadcast rate is 50–75 gal a.i./acre but if only the planted row is to be treated, reduced rates can be used depending on the number of rows to be planted/bed. Applications are made using a spray blade cutting 2–3 inches below the soil surface, depending on soil moisture. Disk hillers follow directly behind the spray blade to form a 3- to 5-inch soil cap over the treated area. After 7–14 days, depending on the rate applied, the soil caps are removed and allowed to air. The label requires a 14-day interval between application and planting. Avoid moving untreated soil into the banded area. This treatment is effective against nightshade and many other weeds. Other methods of application include shank and drench application.
 
B. PARAQUAT* 0.64–1 lb a.i.    
  (Gramoxone Inteon) 2.5–4 pt 12 200
  MODE OF ACTION: A bipyridylium (Group 22)1 herbicide.
  COMMENTS: A nonselective foliar herbicide that kills emerged weeds. Can be used before planting or after planting but before the crop emerges. Any crop plants exposed to the spray will be killed, even germinating seed in the crook stage. No soil residual activity. Use the lower rate on small broadleaf weeds, the higher rate on larger weeds and grasses. Highly toxic if ingested; wear protective clothing. Faster acting on warm, sunny days. For use on seeded onions and garlic.
 
C. GLYPHOSATE 1–4 lb a.i.  
  (Roundup) 1–4 qt 4 —
  MODE OF ACTION: A glycine (Group 9)1 herbicide.
  COMMENTS: A nonselective, foliar herbicide applied before planting to pre-made beds to kill emerged weeds. Allow 3 days after treatment before planting. Use the lower rate for annual grasses and weeds, the higher rate on perennial weeds. Consult the label for specific recommendations on particular weed species. Do not apply to weeds stressed for moisture. For perennial weeds, allow 7 days after application before cultivating.
 
AT PLANTING
A. DCPA 4.5–10.5 lb a.i.  
  (Dacthal) 75W 6–14 lb 12 —
  MODE OF ACTION: A benzoic acid (Group 3)1 herbicide.
  COMMENTS: Apply at planting to control annual grasses and some annual broadleaf weeds. DCPA can be sprayed directly over transplants without injury. In sandy loam soils, maximum preemergence rate of 10 lb/acre is recommended.
 
POSTPLANT
Before weeds emerge
A. DCPA 4.5–10.5 lb a.i.  
  (Dacthal) 75W 6–14 lb 12 0
  MODE OF ACTION: A benzoic acid (Group 3)1 herbicide.
  COMMENTS: For use on onion and garlic. Apply after planting to clean cultivated soil when crop has 4–5 leaves to prevent weed germination. Incorporate with irrigation water, not mechanically. In California, band applications must be used in garlic. Also make band application in onions, except from Aug 1 to Dec 31 when several counties are exempt from this requirement; see label for details. Good control of annual grasses and some annual broadleaf weeds. See label for plantback restrictions. In sandy loam soils, maximum preemergence rate of 10 lb/acre is recommended.
 
B. BENSULIDE 4 lb a.i.  
  (Prefar) 4E 4 qt 12 0
  MODE OF ACTION: A phosphorodithioate (Group 8)1 herbicide.
  COMMENTS: Registered for use on bulb onions and garlic, but recommended only for onions in California. Do not incorporate by mechanical methods.
 
C. PENDIMETHALIN 0.618–1.237 lb a.i.    
  (Prowl) 3.3 EC 1.5–3 pt 24 60
  MODE OF ACTION: A dinitroaniline (Group 3)1 herbicide.
  COMMENTS: For use on garlic, shallots, and bulb onions. Apply after planting garlic, incorporate with sprinklers or a heavy furrow irrigation. Will control many broadleaf weeds and annual grasses. Apply between 2–6 true leaf stage (shallots/onions) and 1–5 true leaf stage (garlic). Do not exceed 3.6 pt/acre/crop. Do not use on muck soils.
 
D. PENDIMETHALIN 0.618–1.237 lb a.i.    
  (Prowl) 3.3 EC 1.5–3 pt 24 60
  MODE OF ACTION: A dinitroaniline (Group 3)1 herbicide.
  ...PLUS...
  OXYFLUORFEN 0.25 lb a.i.  
  (Goal) 2XL 1 pt 24 Onions: 45; Garlic: 60
  MODE OF ACTION: A diphenylether (Group 14)1 herbicide.
 
After crop emerges
A. BROMOXYNIL 0.25–0.375 lb a.i.    
  (Buctril) 1–1.5 pt 12 Garlic: 112
  MODE OF ACTION: A nitrile (Group 6)1 herbicide.
  COMMENTS: Apply by ground when onions have 2–4 true leaves. Use at least 50 gal water in spray mix. Various conditions will lead to crop injury; consult label before application. Can be used in sequence with oxyfluorfen. Very good for control of mustard species.
 
B. OXYFLUORFEN 0.12–0.25 lb a.i.  
  (Goal) 2XL 0.5–1 pt 24 Onions: 45; Garlic: 60
  (GoalTender) 4F 0.25–0.5 pt 24 Onions: 45; Garlic: 60
  MODE OF ACTION: A diphenylether (Group 14)1 herbicide.
  COMMENTS: In onion, apply by ground when onions have 2–4 true leaves. Will control small annual grasses postemergence. Goal has some residual soil activity after application. Very good for control of little mallow (cheeseweed). In garlic, apply it as a directed spray before the last irrigation. Controls nightshade. Will damage foliage if it gets on crop. Garlic must be at least 12 inches in height and weeds should be in the seedling stage and actively growing. The 4F formulation is less active as a burndown material and is most effective on young weeds; causes less damage to crop foliage than the 2XL formulation.
 
C. SETHOXYDIM 0.09–0.28 lb a.i.    
  (Poast) 0.5–1.5 pt 12 30
  MODE OF ACTION: A DIM (Group 1)1 herbicide.
  COMMENTS: A selective, foliar herbicide for control of grasses. A surfactant (crop oil concentrate or nonionic surfactant) is recommended. Safe to the crop. Not effective on drought-stressed grasses or on certain species (e.g., annual bluegrass, sprangletop).
 
D. FLUAZIFOP-P-BUTYL 0.185–0.75 lb a.i.    
  (Fusilade DX) 0.74–3 pt 12 45
  MODE OF ACTION: An FOP (Group 1)1 herbicide.
  COMMENTS: For use on dry bulb onions and garlic. A selective, foliar herbicide for control of grasses. A surfactant (crop oil concentrate or nonionic surfactant) is recommended. Safe to the crop. Not effective on drought-stressed grasses or on certain species (e.g., annual bluegrass, foxtail, sprangletop).
 
E. CLETHODIM 0.10–0.25 lb    
  (Prism) 13–34 fl oz 12 45
  MODE OF ACTION: A DIM (Group 1)1 herbicide.
  COMMENTS: Labeled for use on onion (dry bulb only), garlic, and shallots. Controls annual bluegrass in the 2- to 3-leaf stage as well as other annual and some perennial grasses. Do not apply through any type of irrigation system. Always apply with a crop oil concentrate. Use higher rate on perennial grasses.
 
Layby
A. DCPA 4.5–10.5 lb a.i.    
  (Dacthal) 75W 6–14 lb 12 0
  MODE OF ACTION: A benzoic acid (Group 3)1 herbicide.
  COMMENTS: Labeled for layby applications in garlic. Cultivate before application to remove emerged weeds. Apply as a directed spray when the crop has 4–5 leaves. Do not apply over the top of crop. Good control of annual grasses and some annual broadleaf weeds. Do not incorporate mechanically.
 
 
+  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/.
—  Not applicable.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Onion and Garlic
UC ANR Publication 3453
Weeds
R. Smith, UC Cooperative Extension, Monterey Co.
S. A. Fennimore, Vegetable Crops/Weed Science, UC Davis/Salinas
S. Orloff, UC Cooperative Extension, Siskiyou Co.
G. J. Poole, UC Cooperative Extension, Los Angeles Co.
Acknowledgment for contributions to the weed section:
C. E. Bell, UC Cooperative Extension, San Diego Co.
D. W. Cudney, Botany and Plant Sciences, UC Riverside

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