A common strategy of potato growers is to combine one of the "grass" herbicides listed (EPTC, metolachlor, or pendimethalin) with one of the broadleaf herbicides (linuron or metribuzin). In northern New England, grasses are much less of a problem due to cooler soil temperatures, and often, only a broadleaf herbicide is necessary. If only a broadleaf herbicide is used, clethodim (Select Max), described below, could be used during the growing season to provide emergency or spot treatment of any emerged annual or perennial grasses that were not anticipated.
Yellow Nutsedge. The herbicides that will provide the best control of yellow nutsedge, include a soil-incorporated treatment of EPTC (Eptam), a preemergence application of metolachlor (Dual), or a postemergence application of Metribuzin. The best strategy is to map the problem spots in a field and make an application of either Eptam or Dual before the nutsedge emerges. A postemergence application of Metribuzin can be used to clean any areas that escape the Eptam or Dual treatment. The best time to apply a postemergence treatment of Metribuzin is when the yellow nutsedge is 4-6" tall. Nutsedge is not a grass and will not be controlled by grass herbicides like Poast and Select Max.
Quackgrass. The best strategy for quackgrass control is an application of glyphosate (Roundup) to actively growing quackgrass in the fall prior to planting. An application of Roundup in the spring at least 3 days prior to soil preparation will suppress quackgrass but will not kill it. EPTC (Eptam) and clethodim (Select Max) can also be used to suppress quackgrass during the growing season. Both of these herbicides will provide greater activity if the quackgrass rhizomes (underground storage roots) are cut thoroughly with a disc prior to planting the potatoes. Also, Select Max will provide better suppression of quackgrass if the lower rate is used and repeated when the quackgrass regrows (about 2 weeks after the first application). Be sure to observe the preharvest interval for both Eptam and Select Max.
Stale Seedbed
The following herbicides are nonselective and are used to control weeds which are present in a field prior to planting or before the crop emerges, which is especially useful for the Stale Seedbed Technique (see the Weed Management section for more information).
- glyphosate (Roundup Power Max): PHI 14d, REI 4h, Group 9.
- paraquat (Gramoxone SL 2.0*): REI 48h, Group 22. *Restricted use: Applicators must complete an EPA-approved paraquat training every 3 years: https://www.epa.gov/pesticide-worker-safety/paraquat-dichloride-training-certified-applicators.
- pelargonic acid (Scythe): PHI 1d, REI 12h, Group 0.
Preemergent Herbicides (before weeds germinate)
HRAC Group 3:
ethalfluralin (Sonalan HFP): 1.33 to 2.67 pt/A. REI 24h. Do not exceed 2.67 pt/A per year. Apply broadcast, immediately after planting but prior to crop emergence.
HRAC Group 5:
linuron (Lorox DF): 1.5 to 3 lb/A. REI 24h. 1 application per year. Apply broadcast after planting but prior to crop emergence. If beds are to be dragged and/or hilled, apply after the final dragging or hilling operation. Do not spray over top of emerged potatoes.
HRAC Group 14:
fomesafen (Reflex): 1 pt/A. PHI 70d, REI 12h. 1 application every other year. Apply as a broadcast application after planting but before potato emergence. Do not apply to emerged potato plants.
sulfentrazone (Aquesta 4F): 3 to 8 fl oz/A. REI 12h. 1 application allowed per year. Apply after planting and dragoff but before potatoes emerge. See label for note about incorporation via irrigation and relevant irrigation water pH. Young or stressed crops and some varieties, including Sangre, Shepody, and Snowden, may be damaged by sulfentrazone. Do not apply to emerged potatoes.
HRAC Group 15:
dimethenamid (Outlook): 12 to 21 fl oz/A. PHI 40d, REI 12h. 1 application per year. Can be applied after planting or after drag-off. In cold and wet growing conditions, Outlook application may result in delayed emergence or early-season stunting.
EPTC (Eptam 7E): 3.5 to 7 pt/A. PHI 45d, REI 12h. Do not exceed 14 pt/A per season. Apply to the soil surface before planting , following drag-off, after thinning and clean cultivation, as a directed spray on either side of the crop row, or through irrigation water. Must be incorporated. ‘Superior’ potatoes are sensitive to Eptam and early-season stunting may occur under stress conditions.
Pre- and Postemergent Herbicides
HRAC Group 2:
rimsulfuron (Matrix SG): 1 to 1.5 oz/A. PHI 30d, REI 4hr. Do not exceed 2.5 oz/A per year. Apply before crop emergence after hilling or drag-off, or after crop emergence. Under stressful growing conditions, temporary chlorosis may occur but should not affect yield. See label for instructions for potatoes grown for seed.
HRAC Group 3:
pendimethalin (Prowl H2O): 1.5 to 3 pt/A. REI 24h. 1 application per year. Apply broadcast after planting or drag-off but before potatoes emerge, or from crop emergence to the 6” growth stage. Crop injury may occur if applied after emergence under stressful growing conditions. Do not apply to the ‘White Rose’ potatoes under cool/wet conditions.
trifluralin (Treflan HFP): 1 to 2 pt/A. REI 12h. 1 application per year. Apply after planting either before potatoes emerge, immediately following dragoff, or after potato plants have fully emerged. Incorporate after applying but ensure that treated soil is not concentrated over the bed or covering emerged plants.
HRAC Group 5:
metribuzin (Metribuzin 75): 0.3 to 0.6 lb/A. PHI 60d, REI 12h. Do not exceed 1.3 lb/A per season. May be applied once before and once after crop emergence. Apply broadcast before crop emerges, or broadcast over the top of the crop (but not prior to rainfall or irrigation on recently cultivated potatoes, or within 3 days after periods of wet/cool weather). Do not incorporate into soil. Chlorosis and minor necrosis may occur if applied after crop emerges. Early maturing smooth-skinned white and all red-skinned varieties may be injured by applications after crop emergence. The varieties Atlantic, Bellchip, Centennial, Chipbelle, and Shepody are sensitive to Metribuzin.
HRAC Group 15:
s-metolachlor (Dual Magnum): 1 to 1.67 pt/A. PHI 60d for applications at planting to drag-off, 40d for applications at lay-by, REI 24h. May be applied once before and once after crop emergence. Do not exceed 3.6 pt/A per year. Apply before planting or after planting but before potatoes have emerged, or after potatoes have emerged after hilling/lay-by. Use caution when applying to early maturing potato varieties (see label).
Postemergent Herbicides (after weeds germinate)
HRAC Group 0:
pelargonic acid (Scythe): 3 to 10% solution. PHI 1d, REI 12h. Apply as a vegetative burndown during site preparation, prior to crop emergence from soil, as a directed and shielded spray during crop growth, as a harvest aid, or after harvest.
HRAC Group 1:
clethodim (Select Max): 9 to 32 fl oz/A. PHI 30d, REI 24h. Do not exceed 64 fl oz/A per year. Apply to actively growing grasses.
sethoxydim (Poast): 0.5 to 2.5 pt/A. PHI 30d, REI 12h. Do not exceed 5 pt/A per year. Apply to actively growing grasses. BASF has stopped production and will discontinue the registration at the end of 2027.
HRAC Group 9:
glyphosate (Roundup PowerMax): 10 fl oz to 3.1 qt/A. PHI 14d, REI 4h. Do not exceed 5 qt/A per year. Apply during fallow intervals, prior to planting, at planting, before crop has emerged, or to row middles with a hooded or shielded sprayer or wiper applicator. Spray contact can cause crop death.
HRAC Group 14:
carfentrazone (Aim EC): 0.5 to 2 fl oz/A. PHI 7d, REI 12h. Do not exceed 11.6 fl oz/A per season. Apply during fallow periods, as a preplant burndown, to row middles of emerged crops with a hooded sprayer, or as a harvest aid (up to 5.8 fl oz/A). Contact with crop will cause damage.
HRAC Group 22:
diquat (Reglone): 1 to 2 pt/A. PHI 7d, REI 24h. Do not exceed 4 pt/A per year. For use as a preharvest desiccant. Do not apply to drought-stressed potatoes.
paraquat (Gramoxone SL 3.0*): 0.7 to 1.3 pt/A. REI 48h. Do not exceed 4 pt/A per year. Apply before, during, or after planting, up until ground cracking, as a banded or broadcast application. May be fatal if swallowed or inhaled. *Restricted use: Applicators must complete an EPA-approved paraquat training every 3 years: https://www.epa.gov/pesticide-worker-safety/paraquat-dichloride-training-certified-applicators.