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. 

Stale Seedbed

See Stale Seedbed Technique (page 107).

glyphosate (Roundup Power Max): REI 12h, Group 9.

paraquat (Gramoxone SL 2.0*): restricted use. REI 12h, Group 22. Use 2 – 4 pts/A. 

pelargonic acid (Scythe): PHI 1d, REI 12h, Group 17. Use a 3 -10% solution (3 to 10 gallons per 100 gallons).

Herbicides Used Preemergence to Weeds

DCPA (Dacthal 75WP): REI 12h, Group 3.  Crop should be well established before use.  Apply 4-6 weeks after transplanting or on direct seeded plants at 4-6 inches in height. Will not control emerged weeds.  If weeds have emerged, the crop should be cultivated or weeded prior to application.  Apply 6 to 14 lb/A.  See label to select rate based on target weeds and soil texture.

napropamide (Devrinol 2-XT): REI 12h, Group 15. Apply 2 to 4 qt/A before transplanting, to weed-free soil surface. Use the lower rate on light soil (coarse-textured - sandy) and the higher rate on heavy soil (fine textured - clay). Incorporate thoroughly with irrigation if adequate rainfall does not occur within 24 hours of application. Can be used under plastic mulch.

pendimethalin (Prowl H2O): PHI 21d, 24 hr REI, Group 3. Apply 1 to 3 pt/A, either as preplant incorporated or to the soil surface PRIOR to transplanting. If applied to the soil surface, excessive treated soil falling into the transplant hole may delay crop growth. Can be used under plastic mulch. Can also be applied as a post-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.  Apply before weed germination. Emerged weeds will not be controlled.

s-metolachlor (Dual Magnum): PHI 90d for applications greater than 1.33 pt/A, PHI 30d for applications 1.33 pt/A or less, REI 12h, Group 15.  Used to control annual grasses, yellow nutsedge, nightshade species, galinsoga, and certain other broadleaf weeds.  Apply Dual Magnum before weeds germinate; will not control emerged weeds. Apply Dual Magnum, either preplant incorporated or preplant prior to transplanting tomatoes. If the applied preplant, keep soil disturbance to a minimum during the transplanting. Application may also be made as a directed to spray to tomatoes after the first settling rain/irrigation after transplanting. When an application is made post-directed, apply in a minimum of 20 gallons of water per acre and minimize contact with tomato plants.  If using plastic mulch, apply Dual Magnum preplant non-incorporated to the top of the pressed bed, as the last step prior to laying plastic. Dual Magnum may also be used to treat row-middles in bedded tomatoes, as long as the total amount of Dual Magnum does not exceed the maximum allowed soil type.

  • On coarse soils: 1.0-1.33 pt/A if organic matter content is less than 3% or 1.33 pt/A if organic matter is 3% or greater.
  • On medium soils: apply 1.33-1.67 pt/A.
  • On fine soils: apply 1.33-1.67 pt/A if organic matter content is less than 3% or 1.67-2.0 pt/A if organic matter content is 3% or greater.

trifluralin (Treflan HFP): REI 12h, Group 3.  For transplant tomatoes, apply 1 to 2 pt/A and incorporate before transplanting or apply post-plant as a directed spray to the soil between the rows and beneath plants and incorporate. Select rate based on soil texture; see label for details.  Must be incorporated into the top 2 to 3 inches of the final seedbed within 24 hours of application.  Disc twice after spraying for satisfactory incorporation. See label for info on incorporation recommendations based on different equipment and single pass incorporation. Little or no control of ragweed, galinsoga, mustard or nutsedge.

Herbicides Used Pre- and Postemergence to Weeds

halosulfuron (Sandea): PHI 30d, REI 12h, Group 2. Will provide both preemergence and postemergence control of many weed species. The potential for crop injury is greatest when Sandea is used over transplants grown on bare ground. See the label for other precautions and a list of weeds controlled. Do not apply more than 2 applications or 2 oz/A per 12 month period (Includes applications to the crop and to row middle/furrows).

  • Direct seeded tomatoes: Apply 0.5 to 1 oz/A over the top once tomatoes have reached the 4 leaf stage through 30 days prior to harvest. Applications following bloom could cause some bloom drop under certain environmental conditions. Apply as a directed spray or with crop shield when these conditions are present.
  • Transplanted tomatoes, Pre-transplant: Apply 0.5 to 1 oz/A as a preplant application to bare ground or if using plastic mulch, following final bed shaping and just prior to the installation of the plastic mulch. Tomatoes can be transplanted into treated area 7 days after the application unless local conditions demonstrate safety at an earlier interval. Use lower rate on lighter textured soils with low organic matter. Care should be taken to limit the movement of treated surface soil into the transplant hole during the transplant process, or crop injury can occur.
  • Transplanted tomatoes, Post-transplant: Apply 0.5 to 1 oz/A over the top, post directed, or with crop shields to tomato transplants that are established, actively growing and a minimum of 14 days after transplanting unless local conditions demonstrate safety at an earlier interval. Applications following bloom could cause some bloom drop under certain environmental conditions. Application as a directed spray or with crop shields should be considered when conditions are present.
  • Row Middle/Furrow Applications: Apply between rows for the control of nutsedge and listed broadleaf weeds. Avoid contact of the herbicide with the planted crop. If plastic is used on the planted row, adjust equipment to keep the application off the plastic. Reduce rate and spray volume in proportion to area actually sprayed.
  • Split Applications for Nutsedge: To maximize control of nutsedge, it may be necessary to use a postemergence spot application to those areas where the nutsedge has germinated or regrown.

Pre-transplant followed by postemergence for nutsedge control: For these situations, use a spot treatment method treating only those areas of emerged nutsedge. Application rate should not exceed 0.75 oz/A in these areas. Use a water volume that will allow for good coverage of the weeds.

Postemergence followed by postemergence for nutsedge control: Allow a minimum of 21 days between applications. Application rate should not exceed 1 oz product per treated acre in these areas.

rimsulfuron (Matrix): PHI 60d, 4 hr REI, Group 2. Can be used pre- and postemergence.  Multiple applications permitted, not to exceed 4 oz/A per year.  Can be tank mixed with several herbicides.  See label for details.

  • Preemergence: Apply 2 to 4 oz/A before transplanting.  Activation by a single rainfall or irrigation event (1/2" to 1") is needed within 5 days of application. If rainfall or sprinkler activation cannot be managed, waiting for weeds to emerge and applying postemergence would result in better weed control.  If weeds are present at application, add a nonionic surfactant at 1 to 2 pt/100 gal water. Weak on lambsquarters. If weeds are present at application, the addition of a spray adjuvant may improve weed control.
  • Postemergence:  Apply 1 to 2 oz/A to young, actively growing weeds after crop emergence. Weeds less than 1" in height or diameter at application are most easily controlled. A rainfall or irrigation event (1/3" to 1") no sooner than 4 hours, but not more than 5 days after application, will activate Matrix in the soil and help provide control of subsequent flushes of annual weeds.  Use a surfactant at a minimum rate of 0.25% V/V (crop oil concentrate, methylated seed oils, nitrogen fertilizer solution or nonionic surfactant).  If using multiple postemergence applications, optimum control is seen when the first application is made to small actively growing weeds, followed by a second application 7 to 14 days later.

metribuzin (Metribuzin 75): PHI 7d, REI 12h, Group 5. Do not exceed 1.3 lb/A total per season. Allow at least 14 days between applications. Do not apply within 3 days after periods of cool, wet or cloudy weather, or crop injury will occur.

  • Preplant incorporated (transplanted tomatoes): Apply 0.3 to 0.6 lb/A in at least 10 gallons of water per acre as a broadcast spray to the soil surface immediately before transplanting. Incorporate to a depth of 2 to 4”.
  • Postemergence: One or more applications may be applied/use season (not to exceed 1.3 lb/A per year). Allow at least 14 days between applications or severe crop injury may occur. For transplanted tomatoes, do not apply until transplants have recovered from transplant shock and new growth is evident. Do not apply to tomatoes within 24 hours of application of other pesticides.

Postemergence Broadcast Spray: Apply 0.3 to 0.6 lb/A in at least 20 gallons of water per acre as a broadcast spray over the tops of tomato plants.
Postemergence Directed Spray: This method of treatment should be used for use in fields with a history of severe weed pressure or in fields infested with hard-to-control weeds. Apply 0.6 to 1.3 lb/A in at least 20 gallons of water per acre as a directed spray. Avoid contacting tomato foliage with spray.

Herbicides Used Postemergence to Weeds

carfentrazone (Aim EC): REI 12h, Group 14.  Aim is a burndown herbicide and will injure any foliage it comes into contact with. Apply Aim to areas between rows only 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 inches tall and rosettes less than 3 inches across. Good coverage is essential for good control.  Apply up to 2 oz/A per application, and do not exceed a total of 6.1 oz/ per season. 

clethodim (Select Max): PHI 20d, 24hr REI, Group 1.  Will control grass weeds only. Apply to actively growing grasses.  See label for rate selection.  Multiple applications permitted of 9 to 32 oz/A per application, minimum 14-days between applications, not to exceed 64 oz/A per year.  Add 0.25% v:v nonionic surfactant (1 qt per 100 gal of spray).  Can also be used as a spot-spray by mixing 1/3-2/3% (0.44 to 0.85 oz per gallon) Select Max and 0.25% v:v nonionic surfactant (0.33 oz per gallon).  Spray to wet, but do not allow runoff of spray solution.

paraquat (Gramoxone SL 2.0*): REI 12h, Group 22.  For use between rows after crop establishment. Apply up to 2 pt/A as a directed and shielded spray to emerged weeds between rows when weeds are succulent and weed growth is less than 6”. Maximum 3 applications per year.  Use precision directed spray application equipment adjusted to prevent spray contact with crop plants. Crop contact by the spray will cause severe injury or death. Do not exceed 30 psi nozzle pressure or spray under conditions which may cause excessive drift.

pelargonic acid (Scythe):  PHI 1d, REI 12h, Group 17. Use a 3 -10% solution (3 to 10 gallons per 100 gallons). Use a 3 to 5% solution for annual weeds, a 5 to 7% solution for biennial and perennial weeds, and 7 to 10% solution for maximum burndown. Delivery rate for boom applications should be 75 to 200 gals of spray solution per acre; complete coverage of weed foliage is essential. Use a DIRECTED/ SHIELDED SPRAY; contact with crop will cause injury. For hand-held equipment, spray to completely wet all weed foliage but not to the point of runoff. Repeat applications as necessary. Tank mixes are allowed with this product. See label for complete details.

sethoxydim (Poast): PHI 20d, REI 12h, Group 1.  Controls grass weeds only.  Apply to actively growing grasses (see product label for susceptible stage).  Maximum 1.5 pt/A per application, minimum 14-days between applications.  Do not exceed 4.5 pt/A per year. Use with crop oil concentrate (2.0 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 used as a spot-spray by mixing 1-1.5% (1.3 to 1.9 oz per gallon) Poast and 1% v:v crop oil concentrate (1.3 oz per gallon).  Spray to wet, but do not allow runoff of spray solution.