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

bensulide (Prefar 4E): REI 12h, Group 8.  Apply 5 to 6 qt/A.  Can be preplant incorporated by shallow cultivation (1-2”) or applied preemergence and incorporated by irrigation within 36 hours or application. Grass control only; should be supplemented with cultivation or another registered herbicide for broadleaf control. See label for rotation restrictions. Can be used under plastic mulches.

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. May be applied to transplanted crop only. 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.

pendimethalin (Prowl H2O): PHI 70d, REI 24h, Group 3. Apply 1 to 3 pt/A, either as preplant incorporated or to the soil surface PRIOR to transplanting. Rate based on soil textture; see label for more information.  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.

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 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 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 16 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.

halosulfuron (Sandea): PHI 30d, REI 12h, Group 2. Can be used in row middles/furrows only.  For direct seeded and transplants, apply 0.5 to 1 oz/A to the area between rows as a banded shielded application while avoiding contact with the 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. It is recommended to add 0.25% v:v nonionic surfactant (1 qt per 100 gal of spray) to the spray solution for applications where susceptible weeds are present. Provide both preemergence and postemergence control of many weed species, such as nutsedge and many broadleaf weeds. See the label for other precautions and a list of weeds controlled.

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.  Carrots only. 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.