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Publication #HS193

Weed Management in Bulb Crops (Onion, Leek, Garlic, Shallot)1

Peter Dittmar and William Stall2

Bulb crops are a crop grouping that includes all of the Allium species except chives. Bulb crops include onions (dry and green), leeks, garlic, and shallots. Very few shallots or garlic crops are grown in Florida. Dry bulb onions, green and bunching onions, and leeks are the main crops of this group grown in the state. Where herbicides are limited, the culture of these crops must accommodate cultivation. Bulb crops do not shade out weeds that emerge in the rows. Also, many of the crops, such as dry bulb onions and leeks, require a long growing season. Therefore, a plan for weed control must be made before planting.

Avoid fields that are infested with nutsedge, hard-seeded legumes, or other difficult-to-control weeds. Many weed problems can be reduced by preparing the land well ahead of planting and using Roundup in a "cropping systems" approach, and/or using paraquat in a "stale seed bed" approach. Preemergence and early postemergence herbicides may control many weeds for 4–6 weeks.

Onions and leeks are fairly shallow rooted, and care must be taken not to prune these roots with cultivation, especially when onions begin to bulb. Pulling or hoeing occasional large broadleaf weeds, while labor intensive, may be preferable when plants are older and bulbing.

Emerged grass weeds may be controlled either by Select®, Fusilade®, or Poast®. Care should be taken not to apply any herbicide beyond the preharvest interval specified on the labels.

Herbicide performance depends on weather, irrigation, soil type, and proper selection for the weed species to be controlled. Obtain consistent results by reading the herbicide label and other information about proper application and timing of each herbicide.

Table 1 includes herbicides and directions for application before crop emergence or transplanting. Table 2 lists herbicides for use after crop emergence or transplanting.

Tables

Table 1. 

Preplant / preemergence chemical weed control in onion, leek, garlic, and shallot

Active ingredient

lb. a.i./A

(Trade name)

amount of product/A

Crops

Weeds controlled / remarks

Bensulide

5–6

(Prefar®) 4 E

5–6 qt.

Dry bulb vegetables: onion, garlic, shallot

Annual broadleaf and grass control. Incorporate or irrigate 1–2 inches deep within 36 hrs. of application. Consult label for rotation restrictions.

Bromoxynil

0.25–0.38

(Buctril®) 2 EC

1.0–1.5 pt.

Onion (dry bulb)

Broadleaf weeds. Preemergence is restricted to muck soils containing greater than 10% organic matter. Apply at least 3–4 days prior to emergence. Weeds should not exceed the four-leaf stage, 2 inches in height, or 1 inch in diameter.

Carfentrazone

Up to 0.031

(Aim®) 2 EC

Up to 2 fl. oz.

Onion, garlic, leek, chive, shallot

Emerged broadleaf control. Postdirect hooded application to row middles for burndown of emerged broadleaf weeds. Use crop oil concentrate (COC) or nonionic surfactant (NIS) at recommended rates.

DCPA

4.5–6.0

(Dacthal®) W75

6–8 lb.

(Dacthal®) 6 F

6–8 pt.

Onion (dry bulb, green), leek, shallot

Annual grasses and certain broadleaf control. Apply at seeding or planting. Maximum rate of 10.5 lb. a.i./A per season.

Flumioxazin

Up to 0.06

(Chateau®) 51 WDG

Up to 2 oz.

Onion (dry bulb), garlic

Broadleaf control. Apply to transplanted onions between the two- and six-leaf stage. Apply to direct-seeded onions between the three- and six-leaf stage

Flumioxazin

Up to 0.19

(Chateau®) 51 WDG

Up 6 oz.

Garlic

Broadleaf control. Apply within 3 days of planting garlic.

Glyphosate

(Various formulations)

Consult label

Onion, garlic, leek, chive, shallot

Emerged broadleaf and grass weeds. Consult individual labels for restrictions.

Oxyfluorfen

2.0

(Goal® 2XL) 2 EC

2.0 pt.

(GoalTender®) 4 EC

1.0 pt.

Onion (dry bulb), garlic (dry bulb)

Certain broadleaf weeds. Transplanted only. Apply within 2 days of transplanting. Necrotic lesions, twisting, or stunting of plants can occur if applications are made during cool, wet weather or prior to the full development of the true leaves.

Paraquat

0.5–1.0

(Gramoxone®) 2 SL

2–4 pt.

Onion (dry bulb)

Emerged weeds. Apply prior, during, or after planting, but before crop emerges. Only two applications a season. Use an NIS.

Paraquat

0.63–1.0

(Gramoxone®) 2 SL

2.5–4.0 pt.

(Firestorm®) 3 SL

1.7–2.7 pt.

Onion (seeded), garlic

Emerged broadleaf and grass weeds. Apply as a preplant burndown. A maximum of 1 lb. a.i./A per season.

Pelargonic acid

(Scythe®) 4.2 EC

3%–10% v/v

Onion, garlic, leek, chive, shallot

Emerged weeds. Apply before crop emergence. Product is a contact, nonselective, foliar-applied herbicide. There is no residual activity.

Pendimethalin

0.5–0.75 mineral

1.0–2.0 muck

(Prowl®) 3.3 EC

1.2–1.8 pt. mineral

2.4–4.8 pt. muck

(Prowl® H2O) 3.8

1.0–1.5 pt. mineral

2.0–4.0 pt. muck

Onion (dry bulb), shallot (dry bulb)

Mineral soils: Apply when crop has two to nine true leaves. Muck soils: May be applied as sequential application: preemergence through loop stage, early postemergence (two to six true leaf stage), late postemergence (six to nine true leaf stage). Do not exceed 5.9 lb. a.i./A in a growing season. All soils: Do not irrigate in excess of 0.5 inches after application. Do not apply preemergence through loop stage if heavy rains are expected. PHI 45 days.

Pyraflufen

0.0008–0.003

(ET® Herbicide/Defoliant)

0.5–2.0 fl. oz.

Bulb vegetables

Emerged broadleaf and grass weeds. Apply as a preplant burndown treatment.

Table 2. 

Postemergence chemical weed control in onion, leek, garlic, and shallot

Active ingredient

lb. a.i./A

(Trade name)

amount of product/A

Crops

Weeds controlled / remarks

Bromoxynil

0.25–0.38

(Buctril®) 2 EC

1.0–1.5 pt.

Onion (dry bulb)

Broadleaf weeds. Use at least 50–70 gal. of water/acre. Soil and onion leaves should be dry before application. Waxy coating on leaves reduces chances for injury. Varieties vary in sensitivity and use should be on a trial basis.

Bromoxynil

0.38–0.5

(Buctril®) 2 EC

1.5–2 pt.

Garlic

Broadleaf weeds. Apply after emergence but before 12 inches in height. Weeds are most susceptible up to the four-leaf stage or 2 inches in height or 1 inch wide. PHI 112 days.

Carfentrazone

Up to 0.031

(Aim®) 2 EC, 1.9 EW

Up to 2 fl. oz.

Onion (dry bulb), garlic, leek, chive, shallot

Emerged broadleaf control. Postdirect hooded application to row middles for burndown of emerged broadleaf weeds. Use crop oil concentrate (COC) or nonionic surfactant (NIS) at recommended rates. PHI 0 days.

Clethodim

0.094–0.25

0.07–0.25

(Arrow®, Intensity® One, Select®) 2 EC

6–16 fl. oz.

(Select Max®) 1 EC

9–32 fl. oz.

Onion (dry bulb), garlic, shallot (dry bulb)

Annual and perennial grass control. Some labels include green onion. Use a COC at 1% v/v spray volume. Use an NIS in Select Max®. PHI 45 days.

Clethodim

0.094–0.125

(Arrow®, Intensity® One) 2 EC

6–8 fl. oz.

(Select Max®) 1 EC

12–16 fl. oz.

Chive, leek

Include an NIS in the spray solution. Allow a minimum of a 14-day interval for repeat applications. Do not apply more than 0.5 lb. a.i./A per season. Select Max® is not registered in leek. PHI 14 days.

DCPA

4.5–6.0

(Dacthal®) W75

6–8 lb.

(Dacthal®) 6 F

6–8 pt.

Onion (dry bulb, green), leek, shallot

Annual grasses and certain broadleaf control. Apply at layby up to 14 weeks after planting. If weeds have emerged, cultivate or weed field. Maximum rate of 10.5 lb. a.i./A per season.

Dimethanamid-p

Up to 1.0

(Outlook®) 6 EC

Up to 21 fl. oz.

Onion (dry bulb, green), garlic, leek, shallot (dry bulb, green)

Broadleaf and grass weeds. Apply after the two true leaf stage. Apply as a single application or split application. Split applications of 10–14 fl. oz. followed by 7–10 fl. oz./A with 14 days between applications. Do not exceed 21 fl. oz./A per growing season. PHI 30 days.

Fluazifop

0.188

(Fusilade® DX)

12 fl. oz.

Onion (dry bulb), garlic

Annual and perennial grass weeds. Do not apply more than 48 fl. oz./A per season. Include a COC or NIS in the spray solution. PHI 45 days.

Oxyfluorfen

0.5

(Goal® 2XL) 2 EC

0.5 pt. direct seeded

(GoalTender®) 4 EC

0.25 pt. direct seeded

Onion (dry bulb), garlic (dry bulb

Certain broadleaf weeds. Direct-seeded only. Apply after crop has two true leaves. Multiple treatments can be applied. Do not exceed 0.5 lb. a.i./A. Necrotic lesions, twisting, or stunting of plants can occur if applications are made during cool, wet weather or prior to development of true leaves. PHI 60 days.

Paraquat

0.5

(Gramoxone®) 2 SL

2 pt.

Onion (dry bulb)

Emerged weeds. Row middles only. Only two applications per season. Limit of three applications per year. PHI 60 days

Pelargonic acid

(Scythe®) 4.2 EC

3%–10% v/v

Onion, garlic, leek, chive, shallot

Emerged weeds. Row middles only. Use a shielded sprayer directed to the row middles to reduce drift to the crop.

Pendimethalin

0.5–0.75 mineral

1.0–2.0 muck

(Prowl®) 3.3 EC

1.2–1.8 pt. mineral

2.4–4.8 pt. muck

(Prowl® H2O) 3.8

1.0–1.5 pt. mineral

2.0–4.0 pt. muck

Onion (dry bulb), shallot (dry bulb)

Mineral soils: Apply when crop has two to nine true leaves. Muck soils: May be applied as sequential application: preemergence through loop stage, early postemergence (two to six true leaf stage), late postemergence (six to nine true leaf stage. Do not exceed 5.9 lb. a.i./A per growing season. All soils: Do not irrigate in excess of 0.5 inches after application. Do not apply preemergence through loop stage if rains are expected. PHI 45 days.

Sethoxydim

0.19–0.28

(Poast®) 1.5 EC

1.0–1.5 pt.

Onion, garlic, leek, shallot

Growing grass weeds. Decreased efficacy if weeds are under stress. Do not exceed 4.5 pt./A per season. Include a COC. PHI 30 days.

Footnotes

1.

This document is HS193, one of a series of the Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date March 1999. Revised April 2013. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Peter Dittmar, assistant professor, and William Stall, emeritus professor, Horticultural Sciences Department, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.

The use of trade names in this publication is solely for the purpose of providing specific information. It is not a guarantee or warranty of the product named, and does not signify that they are approved to the exclusion of others of suitable composition.7.9.1


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.