Herbicides Used Postemergence to Weeds

The following herbicides are applied after weeds have emerged. They can be used as the only broadleaf weed control to supplement a soil-applied grass herbicide or they can be used as an emergency treatment if the soil-applied broadleaf herbicide fails to provide adequate control. Timing is very important when using these herbicides. Be careful to check both the ideal weed stage of growth as well as the ideal timing and application precautions for the crop.

bentazon (Basagran): PHI 30d, REI 48h, Group 6.  Apply early post-emergence overtop when weeds are small and corn has 1 to 5 leaves. Rate varies based on weed species targeted (1 to 2 pt/A). See label for info. Bentazon will not control redroot pigweed and will provide only partial control of common lambsquarters, giant ragweed and morning glory. Bentazon should be primarily used as an emergency treatment when a soil-applied broadleaf herbicide has failed. There is less chance of adjacent crop injury from spray drift than with 2,4-D.

carfentrazone (Aim EC): REI 12h, Group 14.  Apply 0.5 to 1 oz/A to actively growing weeds anytime from preplanting until corn is at the 14 leaf-collar stage.  Can be broadcast applied until corn reaches the 8 leaf-collar stage.  For application after corn is at the 8 leaf-collar stage, use drop nozzles to avoid spraying into the whorl and on the corn foliage. Tank mix with atrazine at reduced rates or another broadleaf herbicide to increase the spectrum of weeds controlled. Add non-ionic surfactant at a rate of 1 qt/100 gal spray solution. Expect to see speckling of the crop foliage after application. Initially, the injury appears to be substantial, but it is not systemic and the corn outgrows the injury rapidly. Cultivar sensitivity may vary with Aim. Use caution when treating new cultivars. Weather conditions may also affect the degree of injury observed. Injury may be more severe during periods of warm, cloudy weather with high humidity and plentiful soil moisture when corn growth is rapid and soft. Do not apply more than 2 oz/A per season.  Works best before weeds reach 4” tall or rosettes are 3” in diameter.

clopyralid (Stinger): PHI 30d, REI 12h, Group 4.   For postemergence control of weeds in the composite and legume families. Use Stinger for postemergence control of annual sowthistle, Canada thistle, common cocklebur, common sunflower, giant and common ragweed, Jerusalem artichoke, jimsonweed and other broadleaf weeds infesting field corn.  Apply timing and rates specified on the label. Spray additives are not needed or required by the label and are not recommended. Stinger is a postemergence herbicide with some soil residual activity. Observe replant restrictions on the label or injury may occur from herbicide carryover.

fluthiacet-methyl (Cadet): REI 12h, Group 14. Can be applied as a preplant burndown or after corn emerges as a postemergence weed control.  Can be used anytime until corn is 48” tall or until tasseling occurs. Apply to actively growing weeds before they reach the maximum height listed on the product label for each target weed species.  Does not control grasses, but can be tank mixed with many other herbicides.  See label for details.  Do not exceed 1.25 oz/A per season.  Do not apply to crop under stress or injury may occur. 

nicosulfuron (Accent Q):  REI 4h, Group 2. Apply 0.45 to 1.8 oz/A.  Postemergence grass herbicide.  Works on grasses only.  Best results are obtained when broadcast applied to young, actively growing grasses before corn is 12” tall.  If corn is 12" to 18" high, applications should be made with drop nozzles.   Applications must include either a non-ionic surfactant or crop oil concentrate.  An ammonium nitrate nitrogen fertilizer must also be used unless the label of a potential tank mix partner prevents it.  Do not apply if corn is greater than 18" or 5 leaf collars.  Not all sweet corn varieties are tolerant to Accent.  Check with the Dupont representative or Extension for further information.  Also see the label for optimum sizes of grasses.

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.

tembotrione (Laudis):  REI 12h, Group 27.  Apply 3 fl oz of Laudis per acre postemergence to control many annual broadleaf weeds, including common lambsquarter and triazine-resistant broadleaf weed biotypes, and many annual grasses.  Add oil methylated seed oil (MSO) or concentrate (COC) to be 1% of the spray solution (1 gal/100 gals of spray solution).  In addition, the label requires the addition of nitrogen liquid fertilizer (1.5 qt/A) or AMS (1.5 lb/A).  Tank mix with 0.25 to 1 lb ai/A of atrazine for improved control and to broaden the spectrum of weeds control.  Local university data supports the use of at least 0.5 lb ai/A of atrazine. 

Do not apply tank-mixes of Laudis and atrazine to corn greater than 12" tall.  Do not use postemergence if Callisto, Lumax or Lexar was used preemergence.  Do not tank-mix with Callisto.  Laudis will control/suppress most annual grass species, but may not control certain grass species or grasses larger than the maximum recommended size when treated.  Fall panicum is not controlled by Laudis.  Most broadleaf weeds should be treated before they are 6" tall and grass weeds should be treated before 2" in height.  Laudis has up to an 18 month replant restriction for many vegetables.

topramezone (Armezon): PHI 45d, REI 12h, Group 27.  Absorbed by leaves, roots, and shoots and translocated to the growing points of sensitive weeds to control emerged weeds. Crops under stress may show transient bleaching. These symptoms are temporary and occur infrequently.  Apply up to 1 oz/A when weeds are actively growing, up until corn stage V8.  Controls many annual broadleaf weeds, including common lambsquarter and triazine-resistant broadleaf weed biotypes, and annual grasses.  Postemergence applications of Armezon require the addition of an adjuvant (crop oil concentrate) and nitrogen fertilizer for optimum weed control. Do not use postemergence if Callisto, Lumax or Lexar was used preemergence due to herbicide resistance concerns.  Will control/suppress annual grass species and broadleaf weeds, but may not control species when larger than the maximum recommended size for treatment.  Most broadleaf weeds should be treated before they are 6" tall and grass weeds should be treated before 2" in height.  Use the higher rate to suppress or control panicum species or in rescue applications where the target weeds have grown beyond the size indicated on the label.  Can be tank mixed with 0.25 to 1 lb ai/A of atrazine for improved control and to broaden the spectrum of weeds control.  Local university data supports the use of at least 0.5 lb ai/A of atrazine. 

Perennial Weed Control

Several perennial weed species, including quackgrass, bindweed and milkweed, may be present in a corn field. The grass and broadleaf herbicides described above will have limited activity on these weeds. Use of glyphosate as described below can provide excellent control of these perennial weed species.

glyphosate (Roundup Power Max): REI 12h, Group 9. Apply as a spot treatment BEFORE silking of corn. Do not treat more than 10% of the total field area to be harvested. Any crop plants receiving spray in the treated area will be killed.

Apply AFTER corn harvest to actively growing quackgrass 6" to 8" high. Wait at least 5 days and then plow. Do not plant subsequent crops other than those on the label for 30 days following application. Most effective on bindweed and milkweed at or after bloom.