Weed Control

NOTES: 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. 

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)

DCPA (Dacthal): REI 12h, Group 3. Apply 6-14 lb/A per application, only 1 application per year. Apply directly over transplants 4-6 weeks after transplanting, when crop is well established, and growing conditions are favorable. Can also apply to direct seeded plants when they are 4-6” tall. Rate based on soil texture and organic matter. Cultivate or use herbicides to control emerged weeds before applying.

napropamide (Devrinol 2-XT)REI 24h, Group 0. Apply 2-4 qt/A per application only 1 application per year. Apply to direct seeded or transplanted crops. Shallow incorporate no deeper than the seedling depth. If using with plastic mulch, apply before laying mulch. If soil is dry, incorporate 2-4” into the soil with water through rainfall or irrigation within 24-72 hours of application and then lay mulch the same day the herbicide was incorporated. If applying between rows of plastic mulch, shallow incorporate 1-2” into the soil with water through rainfall or irrigation within 24-72 hours of application.

pendimethalin (Prowl H2O)PHI 21d, REI 24h, Group 3. Apply 1-3 pt/A per application. Rate based on soil texture. Can be applied broadcast before transplanting or as a directed spray after transplanting. Do not apply before direct-seeding. Can be applied to transplanted raised beds just before laying plastic. May also be applied in a band to previously untreated row middles between the transplanted beds but be sure not to overlap row and row-middle spray. Incorporate into the soil or leave on the soil surface. Treated soil falling into the transplant hole may delay crop growth. Can be used under plastic mulch. Can also be applied after transplanting once the roots are established as a directed spray on the soil at the base of the plant, beneath plants, and between rows. Avoid direct contact with foliage or stems or injury will occur. Mechanically incorporate at blocking, thinning, or layby if sufficient rainfall or irrigation has not occurred.

s-metolachlor (Dual Magnum)PHI 30d for applications 1.33 pt/A or less, 90d for applications greater than 1.33 pt/A, REI 24h, Group 15. Apply 1-2 pts/A per application. Only 2 applications allowed if following the 30 days PHI. Rate based on application timing, soil texture, and organic matter content. Can be applied before transplanting tomatoes. Be sure to keep soil disturbance to a minimum during transplanting. If dry weather is expected Dual Magnum ca be uniformly incorporated into the soil before planting. If laying plastic, apply immediately before laying plastic. Can also apply after the tomatoes have emerged in a minimum of 20 gal/A if spray, avoiding contact with the tomato plant. For transplanted tomatoes, apply after the first setting rain or irrigation. For direct seeded tomatoes, apply when tomatoes are at least 4” tall. Can also be applied in row middles.

Has not been tested on all varieties, crop tolerance should be verified before treating the entire field. The risk of crop injury is greater if transplants are damaged or in cool wet conditions. If applying in row middles in sandy soils in wet conditions, epinasty of crops may occur. To reduce this risk, incorporate after spraying, apply 7 or more days before planting transplants, or minimize the application of Dual Magnum onto the plastic mulch.

sulfentrazone (Aquesta 4F): REI 12h, Group 14. Apply 2.25-12 oz/A per application. If transplanting, rate range is 2.25-8.0 oz/A per application. Only 1 application per year. Rate based on soil texture, organic matter and soil pH. Apply banded or broadcast before transplanting.

trifluralin (Treflan HFP)REI 12h, Group 3. Apply 1-2 pt/A per application, only 1 application per year. Can be applied to transplanted tomatoes before or after transplanting, as a directed spray between rows and beneath plants. Incorporate into the soil if applying after tomatoes have emerged. Can be applied to direct seeded tomatoes as a directed spray between rows and beneath plants at the time of blocking or thinning. Rate based on soil texture, percent organic matter, and rainfall.

Pre- and Postemergent Herbicides

halosulfuron (Sandea)PHI 30d, REI 12h, Group 2. Apply 0.5-1 oz/A per application, up to 2 applications allowed per year, a minimum of 21 days apart. Do not exceed 2 oz/A per year. Rate depends on soil texture and organic matter. Split applications will help with control of nutsedge (preemergence followed by post-emergent or two post-emergent applications). In this situation, use a spot treatment to target emerged nutsedge and do not exceed 1 oz/A (or 0.75 oz/A on top of plastic mulch).

Can be applied before transplanting tomatoes (but not before direct seeding). Apply to bare ground or following bed shaping and just prior to installation of plastic mulch. Transplant 7 days after treating, taking care not to expose untreated soil. Can also be applied after tomatoes have emerged either over-the-top, or with crop shields as a directed spray. Apply once tomatoes have reached the 4-leaf stage or once transplants are established, at least 14 days after transplanting. Applications following bloom could cause some bloom drop. Over-the-top applications on plastic mulch are not allowed in the Northeast. Can also apply to row middles.

rimsulfuron (Matrix)PHI 45d*, REI 4h, Group 2. Apply up to 4 oz/A per application, up to 3 applications allowed per year, a minimum of 7 days apart. Do not exceed 4 oz/A per year. Can be used on transplanted or direct seeded tomatoes, but they must be grown outdoors. Can be applied after seeding. Activate and incorporate 2-3” into the soil with water through irrigation or rainfall within 5 days of application. Can also be applied after tomatoes have reached cotyledon stage. Temporary chlorosis may appear but should disappear within 5-15 days. Applying after weed and crop emergence will provide better control if unable to water in a preemergent application. Can also use irrigation or rainfall to activate postemergent Matrix to better control future flushes of weeds. Irrigation or rainfall must occur between 4 hours and 5 days after application.

*Note that some rimsulfuron formulations have a 45d PHI while others have a 60d PHI. Read label carefully and use the correct interval for the product you are applying.

metribuzin (Metribuzin 75)PHI 7d, REI 12h, Group 5. Apply 0.3-1.3 lb/A per application, multiple application allowed per year, a minimum of 14 days apart. Do not exceed 1.3 lb/A per year, but do not apply the total amount of Metribuzin within a time span of 35 days unless using a directed spray. Do not apply within 24 hours of treatment with other pesticides or within 3 days after periods of cool, wet, or cloudy weather. Has not been tested on all varieties, crop tolerance should be verified before treating the entire field. Do not use with hot caps.

Can be applied in a minimum of 10 gal/A of spray as a broadcast application to the soil surface immediately before transplanting. Mechanically incorporate 2-4” into the soil. Place root system below the chemical barrier. Can also be applied after tomatoes have emerged, as a broadcast or directed spray. Apply to transplants once they have recovered from transplant shock and new growth is evident, or to direct seeded tomatoes once they have reached the 5- to 6- leaf stage. If applying at a high rate (0.6-1.3 lbs/A), avoid contact with tomato foliage.

Postemergent Herbicides (after weeds germinate)

carfentrazone (Aim EC)REI 12h, Group 14. Apply up to 2 oz/A per application, multiple applications allowed per year. Do not exceed 6.1 oz/A per year. Can be applied as a preplant burndown no later than 7 days before seeding of immediately before transplanting. Can also be applied to row middles of emerged crops with hooded sprayers to control emerged weeds, including crops grown on mulch or plastic.  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 20d, 24hr REI, Group 1. Apply 9-16 oz/A per application, up to 4 applications allowed 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.

glyphosate (Roundup Power Max): PHI 14d, REI 4h, Group 9. Apply 10 oz to 3.1 qts/A per application, multiple applications allowed per year. Do not exceed 5 qts/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. Allow a minimum of 3 days between application and seeding and do not apply after seeding. 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. Turn air circulation fans off when applying inside a greenhouse.

paraquat (Gramoxone SL 2.0*)restricted use. REI 12h or 24h, Group 22. Apply 1.3-2.7 pts/A per application. Up to 3 applications allowed before tomato planting or emergence, 3 applications after tomato emergence, and 2 applications after harvest as a dessicant, at least 7 days apart. Do not exceed 8 pts/A per year. Can be applied before, during, or after planting but before emergence. Can also be applied after the crop has emerged with a directed spray. Apply in a minimum of 10 gal/A of spray. Can also be applied after the final harvest as a vine dessicant in a minimum of 40 gal/A of spray. May be fatal if swallowed or inhaled. Applicators must complete an EPA-approved paraquat training listed on the following website https://www.epa.gov/pesticide-worker-safety/paraquat-dichloride-training...(link is external). The training must be completed a minimum of every three years.

pelargonic acid (Scythe): PHI 1d, REI 12h, Group 17. Apply a 3-10% solution (3-10 gallons per 100 gallons of spray). Apply in 75-200 gal/A of spray. Can use preplant, or as a directed and shielded spray during crop growth. Avoid contact with foliage or crop damage may occur. Spray to wet, but do not allow runoff of spray solution.

sethoxydim (Poast)PHI 20d, REI 12h, Group 1. Apply up to 1.5 pt/A per application, multiple applications allowed per year, a minimum of 14 days apart. Do not exceed 4.5 pts/A per year. Apply to actively growing grasses. 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.