Lettuce

Agricultural pest management


Common groundsel, Senecio vulgaris, flowers.

Herbicide Treatment Table

(Reviewed 4/17, updated 4/17)

In this Guideline: More about weeds in lettuce:

Herbicide name Amount per acre** REI‡ PHI‡
(Example trade name)   (hours) (days)
Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
The following are listed alphabetically. When choosing a pesticide, consider information relating to environmental impact, resistance management, the pesticide's properties, and application timing. Not all registered pesticides are listed. Always read the label of the product being used.
 
FALLOW
 
A. GLYPHOSATE 0.75–1.5 lb a.i
0.55–1.09 qts
See label See label
  (Roundup Weathermax)      
  WSSA MODE-OF-ACTION GROUP NUMBER1: 9
  COMMENTS: A nonselective foliar herbicide used up to 3 days before emergence of direct-seeded lettuce or before transplanting. Rate depends on weed species and on size. Annual weeds are best controlled when small; control is poor when weeds exceed the maximum size. It gives good annual weed control and some suppression of perennial weeds. Higher application rates are needed for perennial control.
 
B. PARAQUAT* 0.49–1 lb a.i. 24 0
  (Gramoxone SL2.0) 1.3–2.7 pt    
  WSSA MODE-OF-ACTION GROUP NUMBER1: 22
  COMMENTS: A nonselective foliar herbicide without residual activity. Apply as a band treatment over the crop row or as a broadcast treatment before or during lettuce planting. Controls annual weeds and provides some suppression of perennials. Apply when weeds are succulent and from 1 to 6 inches tall; larger weeds are less affected. One to two pints of nonionic surfactant are needed per 100 gal spray solution. Late afternoon applications increase activity. Controls only emerged plants. Do not apply when weather conditions favor drift.
 
D. PELARGONIC ACID 2.25–14 gal/broadcast acre 12 0
  (Scythe) 3%–7% spray solution    
  MODE OF ACTION: Unknown.
  COMMENTS: A contact, nonselective foliar herbicide without residual activity. The degree of control is greater when weeds are actively growing, small, and immature; larger weeds are less affected. Apply as a band treatment over the crop row or as a broadcast treatment at or before planting lettuce. Provides control of annuals and some suppression of perennials. For best results, target weeds should be thoroughly wetted with spray solution but not to the point of runoff. Use 75 to 200 gal spray solution/broadcast acre, with higher volume used when weed density is high. A 3 to 5% solution is sufficient for most annual weeds while perennial or large annual weeds require a 7% solution.
 
PREPLANT
 
A. BENEFIN 1–1.5 lb a.i. 12 0
  (Balan DF) 1.66–2.5 lb    
  WSSA MODE-OF-ACTION GROUP NUMBER1: 3
  COMMENTS: As a preplant treatment for annual weeds, incorporate 2 to 3 inches deep with a disk, rolling cultivator, or power driven rotary tiller (see label). On clay loams or when disking to incorporate, use the higher rate. Take care to assure that treated soil is properly positioned in the finished bed and not pushed off the bed shoulders.
 
B. CARFENTRAZONE Up to 0.03 lb a.i.    
  (Shark) Up to 2.0 oz 12 0
  MODE OF ACTION: 14
  COMMENTS: Can be used as a preplant burn down for transplanted (no later than one day before transplanting) and direct seeded lettuce (no later than 7 days before transplanting). Make application to actively growing weeds up to 4 inches tall or rosettes less than 3 inches across.
 
C. METAM SODIUM* 50–75 gal see label N/A
  (Vapam, Sectagon)
  COMMENTS: A soil fumigant. Beds must be free of large clods and moistened by rainfall or irrigation before application. Soil temperatures should be between 50° and 90°F at a 3–inch depth. Broadcast rate is 50 to 75 gal/acre, but band applications may be made on the bed to lessen the overall application rate. Also used as a bladed application to high-density plantings of baby lettuce plantings on 80-inch wide beds. The label requires a 14-day preplant interval between application and planting. Avoid moving untreated soil into the banded area. Fumigants such as metam sodium are a prime source of volatile organic compounds (VOCs), which are a major air quality issue.
  ... or ...
  METAM POTASSIUM 30–60 gal see label N/A
  (K-Pam, Sectagon K54,)

COMMENTS: Water-soluble liquid that decomposes to a gaseous fumigant (methyl isothiocyanate). Efficacy affected by soil texture, moisture, temperature, and percent organic matter. One gallon of product contains 5.8 lb of metam potassium.

 
D. GLYPHOSATE 0.75–1.5 lb a.i. See label See label
  (Roundup Weathermax) 0.55–1.09 qts    
  WSSA MODE-OF-ACTION GROUP NUMBER1: 9
  COMMENTS: A nonselective foliar herbicide used up to 3 days before emergence of direct-seeded lettuce or before transplanting. Rate depends on weed species and on size. Annual weeds are best controlled when small; control is poor when weeds exceed the maximum size. It gives good annual weed control and some suppression of perennial weeds. Higher application rates are needed for perennial control.
 
E. PARAQUAT* 0.49–1 lb a.i. 24 0
  (Gramoxone SL2.0) 1.96–4 pt    
  WSSA MODE-OF-ACTION GROUP NUMBER1: 22
  COMMENTS: A nonselective foliar herbicide without residual activity. Apply as a band treatment over the crop row or as a broadcast treatment before or during lettuce planting. Controls annual weeds and provides some suppression of perennials. Apply when weeds are succulent and from 1 to 6 inches tall; larger weeds are less affected. One to two pints of nonionic surfactant are needed per 100 gal spray solution. Late afternoon applications increase activity. Controls only emerged plants. Do not apply when weather conditions favor drift.
 
F. PELARGONIC ACID 2.25–14 gal/broadcast acre 12 0
  (Scythe) 3%–7% spray solution    
  MODE OF ACTION: Unknown.
  COMMENTS: A contact, nonselective foliar herbicide without residual activity. The degree of control is greater when weeds are actively growing, small, and immature; larger weeds are less affected. Apply as a band treatment over the crop row or as a broadcast treatment at or before planting lettuce. Provides control of annuals and some suppression of perennials. For best results, target weeds should be thoroughly wetted with spray solution but not to the point of runoff. Use 75 to 200 gal spray solution/broadcast acre, with higher volume used when weed density is high. A 3 to 5% solution is sufficient for most annual weeds while perennial or large annual weeds require a 7% solution.
 
PREEMERGENCE (Before crop emerges)
 
A. PRONAMIDE* 0.5–2 lb a.i. 24 25 to 55
  (Kerb SC) 1.25–5.0 pt    
  WSSA MODE-OF-ACTION GROUP NUMBER1: 3
  COMMENTS: Apply at planting to control annual grasses and broadleaf weeds such as shepherd's-purse and purslane (see susceptibility table). Rate is dependent on soil texture, target weeds and preharvest interval. Lower rates are recommended for sandy soils and for the 25 and 35 day PHI. Incorporate can be mechanical into the top 2 inches (power tiller or rolling cultivator) or by with overhead irrigation. Best applied as a preemergence band application over the top of the finished bed after seeding; promptly sprinkler irrigate with 1 to 2 inches of rainfall or sprinkler irrigation after application for best incorporation. Excessive irrigation on lettuce planted when temperatures are hot may leach pronamide too deeply in the soil to be effective, especially in sandy soils. In some counties, can be applied by chemigation. Is also effective when sprayed on beds and the lettuce stand is germinated by drip irrigation.
 
B. BENSULIDE 5–6 lb a.i. 12 0
  (Prefar 4E) 5–6 qt    
  WSSA MODE-OF-ACTION GROUP NUMBER1: 8
  COMMENTS: Can be applied as a preplant treatment and incorporated uniformly to a depth of 1 to 2 inches before planting. Best applied, however, as a preemergence application over the top of the finished bed after seeding and incorporated with sprinkler irrigation. May also be applied by chemigation through sprinkler or drip irrigation. At least 1 inch rainfall or sprinkler irrigation is needed for best incorporation.
 
POSTEMERGENCE (After crop and weeds have emerged)
 
A. SETHOXYDIM 0.18–0.28 lb a.i. 12 See comments
  (Poast) 1–1.5 pt    
  WSSA MODE-OF-ACTION GROUP NUMBER1: 1
  COMMENTS: Apply in 10 to 20 gal water plus an oil concentrate at the rate of 1 qt/acre. Rates depend on size and weed species. Annual and perennial grasses must be at the proper size and actively growing for good control. Labels recommend not to cultivate within 5 days before application or within 7 days following application. Do not apply with any other pesticide or fertilizer. Do not harvest for 30 days after application on head lettuce or 15 days on leaf lettuce. Follow label instructions regarding use of adjuvants.
 
B. CLETHODIM 0.091–0.12 lb a.i. 24 14
  (Select Max) 12–16 fl oz    
  WSSA MODE-OF-ACTION GROUP NUMBER1: 1
  COMMENTS: For use on leaf lettuce only. Apply in 5 to 40 gal water/acre with 1% v/v crop oil concentrate. For control of annual and perennial grass weeds, including annual bluegrass. Use higher rates on perennial grasses.
 
* Permit required from county agricultural commissioner for purchase or use.
Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
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.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Lettuce
UC ANR Publication 3450

Weeds

R. F. Smith, UC Cooperative Extension, Monterey County
S. A. Fennimore, Weed Science/Plant Sciences, UC Davis/Salinas
M. LeStrange, UC Cooperative Extension, Tulare County

Acknowledgment for contributions to Weeds:
D. W. Cudney, Botany, UC Riverside
W. E. Bendixen, UC Cooperative Extension, Santa Barbara County
C. E. Bell, UC Cooperative Extension, San Diego County
W. T. Lanini, Weed Science/Plant Sciences, UC Davis

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