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. 

Plastic mulch is recommended for sweet potato culture.  It is important to maintain good weed control between the mulched rows before the plants run because once they do run access will be limited.  Also, weedy areas between rows may harbor voles and wireworms.

Stale Seedbed

See Stale Seedbed Technique in the Weed Management section..

  • 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)

clomazone (Command 3ME)PHI 95d, 125d if more than 53.3 oz used, REI 12h, Group 13. Apply 21.3-64 oz/A per application, only 1 application per year. Apply in a minimum of 10 gal/A of spray. Use the lower rate on sandy soils and the higher rate on silt and clay soils. Can be applied after transplanting, before weed emergence. Some temporary crop injury (partial whitening of leaf or stem tissue) may be visible after crop emergence. Complete recovery will occur from minor early injury without affecting yield or earliness.

DCPA (Dacthal W-75)REI 12h, Group 3. Apply 6-14 pts/A per application, only 1 application per year. Rate based on soil texture and weed composition. Can be applied at transplanting or at layby.  Can be sprayed directly over transplants without injury. Layby applications can be made up to 6 weeks after transplanting. Rates depend on soil type and organic matter. If weeds emerge prior to layby, the sweet potato should be cultivated or weeded prior to application. Incorporation not recommended.

flumioxazin (Valor SX):  REI 12h, Group 14. Apply up to 3 oz/A per application, only 1 application per year. Apply to soil before transplanting sweet potato slips. Do not use on any sweet potato variety other than “BEAUREGARD”, unless user has tested Valor SX on other variety and has found crop tolerance to be acceptable. Do not use greenhouse grown transplants. Do not use transplants harvested more than 2 days prior to transplanting.

napropamide (Devrinol 2-XT)REI 24h, Group 0. Apply 2-4 qt/A per application, only 1 application per year. Use the lower rate on sandy soils and the higher rate on silt and clay soils. Apply after transplanting to a weed free soil surface. Activate and incorporate 2-4" into the soil with water through irrigation or rainfall within 24 – 72 hours of application. Can also be applied and incorporated 1-2’’ into the soil through shallow cultivation.

dimethenamid (Outlook)PHI 40d, REI 12h, Group 15.  Apply 7-21 oz/A per application, only 1 application allowed per year. Apply after planting or drag-off. Can cause delayed emergence or temporary stunting in cold and wet conditions. Can cause crop injury to sweet potatoes, so be careful not to allow herbicide to come into contact with tubers. Apply when the potential for loss due to weeds is higher than potential loss due to herbicide injury.

Postemergent Herbicides (after weeds germinate)

carfentrazone (Aim EC)PHI 7d, 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 1 day after seeding. 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. Can use up to 5.8 oz/A as a harvest aid, but do not exceed the maximum of 6.1 oz/A per year. Adequate desiccation is achieved within 14 days after application.

clethodim (Select Max)PHI 30d, 24hr REI, Group 1. Apply 6-32 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.

fluazifop (Fusilade DX)PHI 14d, REI 12h, Group 1. Apply up to 12 oz/A per application, up to 4 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 PowerMax)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. 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. Can also be applied with the wiper method using a 33% solution by volume. A maximum of 5 wiper applications allowed per year, a minimum of 14 days apart and 7 days prior to harvest.

paraquat (Gramozone SL 3.0*): restricted use. REI 12h or 24h application type, Group 22. Apply 0.7-1.3 pts/A per application, up to 3 applications allowed per year, a minimum of 7 days apart. Do not exceed 4 pts/A per year. Can be applied before, during, or after planting but before emergence (up until ground cracking). Apply in a minimum of 10 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 24h, REI 12h, Group 0. 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.