Weed Control

NOTE:  For the herbicides listed below, one product trade name and formulation is provided for each active ingredient along with preharvest interval (PHI), restricted entry interval (REI), resistance management group number, and example of rates and special instructions. In many cases, there are other products available with the same active ingredient. However, not all products with the same active ingredient are registered for use in a crop. Always check the product label to be sure that the crop is listed before using. 

See section on Soil Fumigation Outdoors in the Disease Management section. Proper use of Vapam can provide control of most weed species.

Stale Seedbed

See Stale Seedbed Technique for information on the use of these herbicides or flaming.

  • carfentrazone (Aim EC): PHI 0d, REI 12h, Group 14.
  • glyphosate (Roundup Power Max): PHI 14d, REI 4h, Group 9.
  • paraquat (Gramoxone SL 2.0*): restricted use. REI 12h or 24h, Group 22.
  • pelargonic acid (Scythe): PHI 1d, REI 12h, Group 0.

Preemergent Herbicides (before weeds germinate)

bensulide (Prefar 4E)REI 12h, Group 0. Apply 5-6 qt/A per application, only 1 application per year. Do not exceed 6 qt/A per year. Can be applied before planting or after planting before crop has emerged. Incorporate 1-2” into the soil within 36 hours by shallow cultivation or with water through irrigation or rainfall. Grass control only; should be supplemented with cultivation or another registered herbicide for broadleaf control.

pronamide (Kerb SC)PHI 55d, REI 24h, Group 3. For head lettuce, endive, escarole, and radicchio greens only. Apply 2-4 lbs/A per application, only 1 application per year. Can be applied either before or after planting, before crop emergence as a banded, bed-topped, or broadcast application in 20-50 gal/A of spray. If applied when air temperatures exceed 85°F it must be shallow incorporated within 1-2 days. Incorporate Kerb into the soil with shallow cultivation or water through irrigation or rainfall. There must be 1-2“ of irrigation immediately after application, or 0.5-1” of rainfall within 3 days. Rate based on soil texture, weed composition, incorporation method, and crop variety. Do not apply to leaf lettuce. Has not been tested on all varieties, crop tolerance should be verified before treating the entire field.

trifluralin (Treflan HFP)REI 12h, Group 3. Endive and escarole only. Apply 1-2 pts/A per application, only 1 application per year. Apply in spring or early summer, before planting. Rate based on soil texture and crop. Incorporate 2-3’’ into the top of the final seedbed within 24 hours of application. Disc twice after spraying for satisfactory incorporation.

Postemergent Herbicides (after weeds germinate)

carfentrazone (Aim EC)REI 12h, Group 14. Apply 0.5-2 oz/A per application, multiple applications allowed per year. Do not exceed 6.1 oz/A per season. Can be applied as a preplant burndown or to row middles of emerged crops with hooded sprayers to control emerged weeds. If used as a preplant burndown, use up to 2.0 fl oz/A no later than 7 days before planting by seed or immediately before planting transplants. Prevent any spray from contacting the crop, or injury will occur.  For best results, make application to actively growing weeds up to 4” tall and rosettes less than 3” across.

clethodim (Select Max)PHI 14d, REI 24h, Group 1. Apply 9-16 oz/A per application, up to 4 applications per year, a minimum of 14 days apart. Do not exceed 64 oz/A per year.  Apply to actively growing grasses. Add 0.25% v:v nonionic surfactant (1 qt/100 gal of spray).  Can also be applied as a spot-spray by mixing 0.33-0.66% (0.44-0.85 oz/gal) Select Max and 0.25% v:v nonionic surfactant (0.33 oz/gal).  Spray to wet, but do not allow runoff of spray solution.

fluazifop (Fusilade DX): PHI 14d, REI 12h, Group 1. For lettuce (leaf and head). Apply up to 24 oz/A per application, up to 2 applications allowed per year, a minimum of 14 days apart. Do not exceed 48 oz/A per year.  Apply to actively growing grasses (see product label for susceptible stage). Add either crop oil concentrate (0.5-1%, 0.5-1 gallon per 100 gallons of spray) or nonionic surfactant (0.25-0.5%, 1-2 qt per 100 gal of spray).

glyphosate (Roundup Power Max): PHI 14d, REI 4h, Group 9. Apply 10 oz-3.1 qt/A per application, multiple applications allowed per year. Do not exceed 5 qt/A per year. Rate based on target weed species. Can be applied during fallow intervals, prior to planting or transplanting, at planting, or before crop has emerged. Avoid any contact of herbicide with foliage, green shoots, stems, bark, exposed roots, or fruit of crops, or crop death could result. Could cause injury when applied prior to transplanting or direct-seeding into plastic mulch. Remove residual product from plastic mulch with a 0.5” of water through irrigation or rainfall prior to planting. For any crop not listed on the label, any application must be at least 30 days prior to planting.

pelargonic acid (Scythe): PHI 1d, REI 12h, Group 0. Apply a 3-10% solution (3-10 gallons per 100 gallons of spray). Rate based on target weed species. Apply in 75-200 gal/A of spray or with a spot sprayer until foliage is wet but not to the point of runoff. Repeat applications as necessary. Can apply for vegetative burndown during site preparation, prior to crop emergence from soil, as a directed and shielded spray during crop growth taking care to avoid contact with foliage and green tissue of crops, or as a harvest aid and desiccant to remove crop leaves or ease harvest.

sethoxydim (Poast): PHI 30d for head lettuce, 15d for leaf lettuce, escarole, and endive, REI 12h, Group 1. Apply 1.5 pt/A per application, multiple applications allowed per year. Do not exceed 3 pts/A per year. Apply to actively growing grasses. Application rate is dependent on weed species composition and height. Use with crop oil concentrate (2 pt/A) or methylated seed oil (1.5 pt/A). Note that crop oil can cause injury under hot and humid conditions. Can also be applied as a spot-spray by mixing 1-1.5% (1.3-1.9 oz/gal) Poast and 1% v:v crop oil concentrate (1.3 oz/gal). Spray to wet, but do not allow runoff of spray solution.

paraquat (Gramozone SL 3.0)REI 12h or 24h, Group 22. Apply 1.3-2.7 pt/A per application, up to 3 applications allowed per year, at least 7 days apart. Apply before, during, or after planting, but before emergence as a banded or broadcast application in a minimum of 10 gal/A of spray. Minimize soil disturbance when seeding.