acetochlor (Surpass): REI 12h, Group 15.  Not for use in New Hampshire. Works to inhibit weed seed germination, and will not work on emerged weeds.  Labeled for control of annual grasses and broadleaf weeds.  Can be used early preplant, preplant incorporated, preemergence, postplant-preemergence, and early crop postemergence.    Rates based on both soil texture and tillage system used (conventional, reduced, or no-till).  Read label for proper rate selection. Also see label for herbicides approved as tank-mixing partners. 

dimethenamid (Outlook): PHI 50d, REI 12h, Group 15.  May be applied preplant surface, preplant incorporated, preemergence, or postemergence to corn up to 12-inches tall. May be applied as a single application or two split applications.  See Table 2. of product label to select correct rate for your soil texture and organic matter content. A split application may be used (8 to 16 fl oz/A per application, not to exceed 24 fl oz/A per year).  Allow a minimum of 14 days between applications. First application can be applied preplant, preemergence, or postemergence, then apply the remainder (8 to 16 oz/A) of the seasonal maximum rate during the second application (postemergence).  Can be tank-mixed with many other herbicides, see label for details.  Check with seed supplier for potential varietal susceptibility to injury. Outlook is a selective residual herbicide for controlling many annual grasses, annual broadleaf weeds, and sedges as they germinate. Will not control emerged weeds.

pendimethalin (Prowl H2O): REI 24h, Group 3. Apply before weed germination. Emerged weeds will not be controlled.  Work against annual grasses and some broadleaf weeds.  Can be used after planting but before weeds germinate and crop emerges, or after corn emerges until it is 20 to 24-inches tall or at V8.  Rate based on soil texture, see label for details.  When used after planting, there is potential for crop injury if herbicide is moved into the seed zone.  Minimize the potential for crop injury by preparing a firm seedbed and planting corn seed at least 1.5" deep.  If heavy rains follow an application to dry soil, Prowl can move to the seed zone and cause crop injury. Specific weeds for which this herbicide should be considered include triazine-resistant lambsquarters, and velvetleaf. 

pyroxasulfone (Zidua): PHI 37d, REI 12h, Group 15.  A root-and-shoot growth inhibitor that controls susceptible germinating seedlings before or soon after they emerge from the soil. Application rates vary depending on soil texture, see label for details. May be applied preplant surface, pre-plant incorporated, preemergence, or early postemergence to corn for residual preemergence control of weeds. See label for application instructions for each timing.  Plant corn seed at least 1" deep.  Labeled for use against many annual grasses and broadleaf weeds. Controls most annual grasses including crabgrass, panicum, foxtails, and barnyardgrass.  Weak on common lambsquarters but will control redroot pigweed, carpetweed, nightshade, and common purslane.  Has activity on yellow nutsedge. 

s-metolachlor (Dual Magnum):  PHI 30d, REI 12h, Group 15.  Can be used either preplant surface, preplant incorporated, preemergence, or lay-by.  See label for application instructions and rates based on timing and soil type. 

simazine (Princep): PHI 45d, REI 12h, Group 5. Apply up to 2 qt/A preplant incorporated or to the soil surface immediately after planting before corn emerges. Use alone only if annual grasses are not a problem.  Do not apply on highly erodible soils unless there is at least 30% plant residue cover. 

2,4-D (Amine 4): PHI 45d, REI 28h, Group 4.   Can make one preplant or preemergence application per crop cycle. Apply up to 2.14 pt/A (1.0 lb ae/acre) to soil anytime after planting but before corn emerges. Can make one postemergence application per crop cycle. Apply a maximum of 1.07 pt /A (0.5 lb ae/acre) per application. Use drop nozzles to direct spray toward base if corn is over 8" tall. Do not apply from 7 to 10 days before tasseling to dough stage. Allow a minimum of 21 days between applications. Use a maximum of 3.2 pts/acre (1.5 lbs ae/acre) per year. Reduce rate of 2,4-D if temperature is hot and soil is wet. Use only the amine formulation of 2,4-D; Do not use any ester or low-volatile ester formulations. Use all precautions to avoid spray drift to desirable broadleaf crops.

atrazine (Aatrex 4L): REI 12h, Group 5.  Apply preplant incorporated or to the soil surface immediately after planting. Use alone only if annual grasses are not a problem.  Shallow cultivation may help to control annual broadleaf weeds. May be tank mixed with any of the preemergence grass herbicides listed above as well either glyphosate or paraquat for burndown of existing weeds.

For postemergence applications, add either 1 qt/A of crop oil concentrate or 1 gal/A of spray oil. Apply when weeds are 1 to 1 1/2" high and before corn is 12" high. This treatment can be used as the primary broadleaf herbicide treatment instead of an application at planting or it can be used as an emergency treatment if the soil-applied broadleaf herbicide treatment failed. If applied correctly, this application will control the emerged weeds and will continue to provide residual control for later-emerging broadleaf weeds. Check label for additional precautions regarding the use of crop oil and petroleum oils.

Only 1 lb active ingredient of atrazine is recommended for sweet corn in New England. This is well below the rate on the label and constitutes best management practices for groundwater protection. This rate could be reduced further, although the grower should be prepared to make a second application of atrazine if any weeds escape.

halosulfuron (Sandea): PHI 30d, REI 12h, Group 2.  Apply 2/3 to 1 oz/A over the top or with drop nozzles from the spike through layby stage of the corn.  If necessary, a sequential treatment of this product at 2/3 oz/A acre may be applied only with drop nozzles semi-directed or directed to avoid application into the corn plant whorl.  Do not apply more than 2 applications per year.  Do not use on “Jubilee” sweet corn.  Other varieties may also be sensitive to injury.  The use of non-ionic surfactant is recommended for use on emerged weeds (1 to 2 qt/100 gal spray). Works on germinating broadleaf weed seeds, and also on emerged broadleaf weeds.  Control varies with type and size of weed.  Species listed on the label include redroot pigweed, pokeweed, common ragweed, Pennsylvania smartweed, common sunflower, velvetleaf, wild mustard, yellow nutsedge, and wild radish. Do not cultivate for 7 days after application.

mesotrione (Callisto): PHI 45d, REI 12h,  Group 28.  May be applied by ground for preemergence or postemergence weed control.  See label for list of susceptible species. Callisto provides excellent control of many problem broadleaf species such a velvetleaf and triazine-resistant lambsquarters.  Callisto provides only partial control of yellow nutsedge and no control of ragweed when applied postemergence.

Make a single preemergence application of 6.0-7.7 oz/A after seeding to the soil surface. Can be tank mixed with many other herbicides, and it also included in some premixed products.  See label for details. Use 5 to 6 oz/A if tank mixing with atrazine. In a tank mix, the atrazine rate can be reduced to 0.5 to 1 pt/A.  A grass herbicide must also be used. On cool soils in the spring, Callisto may be a better option than using Prowl to control these two weed species. Callisto does not provide preemergence control of yellow nutsedge. With this weed, it is important to continue to use atrazine (alone or in combination with Callisto) as well as either Dual, Outlook, or Zidua preemergence. See the label for precautions and more information on tank mixes, rates, and weeds controlled.

For postemergence weed control, apply 3 oz/A to corn up to 30" tall when weeds are no more than 3" tall.  Include a nonionic surfactant.  Do not make more than 2 applications per season to corn and do not exceed a total of 7.7 oz/A of Callisto. Applications should be a minimum of 14 days apart.  Use other options if these weeds are present. See the label for precautions and more information on tank mixes, rates, and weeds controlled.  Severe corn injury resulting in yield loss may occur if any organophosphate or carbamate insecticide is applied foliar postemergence within 7 days before or 7 days after Callisto application.  May cause crop bleaching in some yellow popcorn and sweet corn hybrids. Crop bleaching is typically transitory and has no effect on final yield or quality.

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.  Not for use in New Hampshire. 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.

tolpyralate (ShieldEx 400 SC): PHI 35d, REI 12h, Group 27. Can control or suppress the growth of many young and actively growing broadleaf and grass weeds. See label for list of susceptible weeds. Apply up to 1.35 fl oz/A when corn is up to the 6 leaf collar (V6) stage or up to 20 inches tall, whichever is more restrictive. Up to two applications are permitted at least 14 days apart. Not to exceed 2.7 fl oz/A per year. Use an adjuvant for optimum activity (refer to adjuvant section of label for details). Rainfast within 1 hour after application.

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.

Many corn herbicides can be tank mixed with one or more other herbicides to extend the spectrum of weed control.  Labels will have detailed instruction about compatible tank mixing partners and instructions on selecting rates, etc. when tank mixing.

Formulated Mixes (Prepackaged Tank Mixes)

In recent years, many products have come on the market as prepackaged combinations of herbicides which were often recommended in the past as tank-mix combinations of products purchased separately. They are designed for to expand the spectrum of control (i.e. grass herbicide mixed with broadleaf herbicide). 

There are 3 questions that a grower or pesticide applicator should ask when deciding whether to use a formulated mix or the individual herbicide.

1. Which is less expensive on a per acre basis?
2. Which formulation is easier to apply? Most pesticide applicators prefer to avoid wettable powders, for example.
3. Is the ratio of the two herbicides in the formulated mix appropriate for the given field situation? For example, Bicep Lite contains 2/3 as much atrazine as Bicep and should allow growers a better opportunity to obtain good grass control without using more atrazine than is needed.

Following are some examples of formulated mixes registered for use on sweet corn. There are many others in addition to those listed.