Weeds

The major weeds found in North Carolina sweet potato plant beds and fields are annual grasses, pigweeds, common cocklebur, common lambsquarters, common ragweed, Pennsylvania smartweed and nutsedge. Weeds are slightly more common in sweet potato plant beds than in fields. Weeds in plant beds can reduce plant numbers and weight. In fields, severe weeds can reduce yields by 100 percent, as well as diminish sweet potato root quality and interfere with harvest. Sweet potato producers have only two options for controlling weeds in plant beds: hand weeding and herbicides. Annual grasses are easily controlled in plant beds with the use of herbicides, but broadleaf weeds are difficult to control. In fields, growers have four options for tackling weeds: pre-plant tillage, herbicides, cultivation, and hand weeding.

For each field you should know the weed problems expected, the soil type, the time of planting, and the cultural practices you plan to use before selecting herbicides. Applying chemicals at the wrong time or at a rate that is excessive for the soil type can cause injury. In soils low in organic matter (less than 2 %) use the lowest rates suggested on the herbicide labels. To help minimize the effects of adverse weather and the potential for injury, use herbicide rates that are appropriate for the soil type in the field.

Plant Beds Pre-emergence control:

  • Napropamide (Devrinol 50DF @1-2 lb active ingredient per acre) is labeled for preemergence control of annual grasses and small-seeded broadleaf weeds such as common purslane and pigweed.
  • Clomazone (Command 4EC @0.75-1 lb active ingredient./acre) is labeled for preemergence control of annual grasses and small-seeded broadleaf weeds such as velvetleaf, common ragweed, common lambsquarters and prickly sida. It does not control pigweed.

Plant Beds Post-emergence control:

  • Fluazifop (Fusilade DX 2EC @0.1-0.25 lb active ingredient/acre) is labeled for postemergence control of annual and perennial grasses. It does not control broadleaf weeeds or sedges.
  • Sethoxydim (Poast 1.53 EC @0.2-.0.3 lb active ingredient/acre) is labeled for postemergence control of annual and perennial grasses. It does not control broadleaf weeds or sedges.

Fields Pre-plant Control:

  • Fields are prepared for sweet potato planting approximately 2 weeks before planting, and weeds often emerge between field preparation and planting. Thus, growers in North Carolina rework their fields just before transplanting to control weeds.
  • Gyphosate (Roundup 4L @0.75-1 lb active ingredient/acre) is labeled as a preplant application in Sweet Potato fields for the control of emerged weeds. It is used on approximately 1 to 2 percent of the acreage.

Fields Pre-emergence control:

  • Valor (flumioxazin) 2.5 oy 2-5 days prior to transplanting; do not incorporate.
  • Clomazone (Command 4 EC@ 0.75-1 lb active ingredient/acre) is labeled for preemergence control of annual grasses and small-seeded broadleaf weeds such as velvetleaf, common ragweed, common lambsquarters, and prickly sida. It does not control pigweed.
  • EPTC (Eptam 7E@ 1.75-3.5 lb. active ingredient/acre) is labeled for preemergence control of yellow and purple nutsedge and is more than 85 percent effective. It is used primarily for control of these weeds since no herbicide labeled for SweetPotatoes, except EPTC, will control nutsedge. EPTC must be preplant-incorporated. It is sometimes applied with clomazone.
  • Napropamide (Devrinol 50DF @1-2 lb. active ingredient/acre) is labeled for preemergence control of annual grasses and small-seeded broadleaf weeds such as common purslane and pigweed. Napropamide is sometimes mixed with clomazone for improved pigweed control because the action is better than with clomazone alone.

Fields Post-emergence Weed Control:

  • Fluazifot (Fusilade DX2EC@0.1-2. You need JavaScript enabled to view it.5 lb active ingredient/acre) is labeled for control of broadleaf weeds or sedges.
  • Sethoxydim (Poast 1.53 EC @ 0.2-0.3 lb active ingredient/acre) is labeled for postemergence control of annual and perennial grasses. It does not control broadleaf weeds or sedges.