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 (page 107).

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

paraquat (Gramoxone SL 2.0*): restricted use. REI 12h, Group 22. Use 1 – 2 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

clomazone (Command 3ME): PHI 95d if < 3.3 pt/A used, PHI 125d if > 3.3 pt/A used, REI 12h, Group 13.  Use the lower specified rate on coarse soils and the higher specified rate on fine soils. Refer to the soil texture chart on label.  Can be applied to the soil surface prior to planting at 1.3 to 4.0 pt/A, or post-transplant to the crop and prior to weed emergence at a maximum of 4.0 pints per acre.  Will control annual grasses and many broadleaf weeds including common lambsquarters, velvetleaf, and jimsonweed. 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. See label for replanting restrictions.

DCPA (Dacthal 75WP): REI 12h, Group 3.  Select rate for preemergence use based on soil type and weeds targeted for preemergence control.  Good control of most annual grasses; fair on redroot pigweed, lambsquarter, and purslane.  Apply to weed-free soil; will not control existing weeds.  Can be applied at transplanting and/or at layby.  Can be sprayed directly over transplants without injury. Lay by applications can be made up to 6 weeks after transplanting.  If weeds emerge prior to layby, the onions should be cultivated or weeded prior to application. Preplant incorporation not recommended.

flumioxazin (Valor SX):  REI 12h, Group 14.  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. Apply up to 3 oz/A to soil prior to transplanting sweet potatoes slips for the preemergence control of weeds. Do not use greenhouse grown transplants. Do not use transplants harvested more than 2 days prior to transplanting.

napropamide (Devrinol 2-XT): REI 12h, Group 15.  Apply 2 to 4 qt/A.  Use the lower rate on light soil (coarse-textured - sandy) and the higher rate on heavy soils (fine textured - clay).  Apply to the soil surface after transplanting and wet the soil to a depth of 2" to 4" within 24 – 72 hours to activate.

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 30d, 24hr REI, Group 1.  Will control grass weeds only. Apply to actively growing grasses.  See label for rate selection. Multiple applications of 9 to 32 oz/A per application, minimum 14-days between applications, not to exceed 64 oz/A per year.  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.

fluazifop (Fusilade DX): PHI 14d, REI 12h, Group 1.  For grass weed control only. Apply up to 12 oz/A.  See label to select rate based on grasses targeted for control. Allow for minimum 14 days between applications, and not to 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).