# Select corn herbicides by crop traits, growth stage and volunteer-corn risk URL: https://leafwrit.com/us/corn-herbicide-selection/ Reviewed: 2026-10-29 ## Corn herbicide selection: crop stage, hybrid traits and weed species decide the product Preemergence herbicides applied at planting are likely no longer active after a month of heavy rain, and delayed postemergence applications may call for late-season weed control to protect yield, prevent harvest difficulties and reduce additions to the weed seed bank. Atrazine is not labeled for corn 12 inches tall or taller. ### Corn preemergence herbicides (pre emergent) and postemergence herbicides for corn Programs that combine pre- and postemergence herbicides with multiple modes of action are compared for Palmer amaranth control in corn; the choice rests on herbicide chemistry, performance and cost. The label sets who may use a pesticide and where, how, how much and how often it may be used. ### Preplant herbicide for corn A preplant herbicide for corn goes on before the crop is planted. On the label of the exact product, find how long before planting it may be applied and what it leaves in the soil for the next crop; the plantback intervals are collected on the [herbicide plantback and grazing restrictions](/us/herbicide-plantback-grazing-restrictions/) page. Preemergence products applied at planting follow the separate timing in the section above. ### Post emergent corn herbicide limits by corn height and stage Before spraying, measure the corn's height, count its leaf stage and write both down rather than going by the calendar date. Then compare them with the limit of the exact product and with any restriction for your hybrid. Take along the hybrid, the weed species and sizes, and what has already been sprayed on the field. For a granular product, ask for that product's own directions and application-equipment instructions instead of reusing a liquid spray setup. Products labeled for corn over 12 inches tall, with the maximum corn height or stage: - Glufosinate (group 10, Liberty): V6. - Tolpyralate (group 27, Shieldex): V6 or 20 inches. - Clopyralid (group 4, Stinger): 24 inches; fair to good pigweed control. - Topramezone (group 27, Armezon, Impact): V8. - Pyridate (group 6, Tough): V8; can be added to group 27 herbicides in place of atrazine. - Mesotrione (group 27, Callisto): V8 or 30 inches. - Glyphosate (group 9): V8 or 30 inches. - Nicosulfuron (group 2, Accent): 36 inches. - Tembotrione (group 27, Laudis): V9. - Carfentrazone (group 14, Aim): 14 leaves. - Bromoxynil (group 6): tasseling; fair pigweed control. - Dicamba (group 4): tasseling; fair to good crop safety. DiFlexx stops at V10; Status stops at V8 or 30 inches. - 2,4-D (group 4): tasseling. Enlist One stops at V8 or 30 inches and is for Enlist corn hybrids only. ### Drop nozzles in late-season corn Some products recommend or require drop nozzles to reduce crop injury and improve spray coverage on weeds shorter than the crop. Nicosulfuron needs drop nozzles above 20 inches, carfentrazone above 8 leaves, and 2,4-D when corn is taller than 8 inches. Glyphosate on RR2 hybrids uses drop nozzles at 30 to 48 inches. If a late-season product needs them, ask the operator which machine and nozzle height will be used and how the spray will reach the weeds under the canopy; do not assume every late pass uses the same height, angle or dose. ### Corn weeds: grass herbicide for corn and weed control by weed species Glufosinate does not control large or well-tillered grasses such as yellow foxtail, wild oat or volunteer cereals, and it is non-residual, so several weed flushes may need more than one application or a residual partner. Glyphosate applied alone or after only one application may not control kochia, nightshades, wild buckwheat, horseweed (marestail), dandelion or common lambsquarters. Write down the grass species and their size before choosing a product, and check the candidate's directions against your hybrid's traits. Poast Protected corn hybrids tolerate over-the-top sethoxydim products (Poast, Poast Plus, Rezult), which control annual grasses when applied with other postemergence herbicides. ### Giant ragweed control in corn For giant ragweed control in corn, write down the height of the ragweed and the stage of the corn on the day of the pass, then look for giant ragweed (*Ambrosia trifida*) in the weed list of the product's label and compare the maximum weed height it gives. The product list above shows the corn height each product allows. Do not pick a product by the corn limit alone; a tall ragweed stand can be past the weed-size limit while the corn is still within its own. ### Weeding in maize: maize weeding herbicide, Syngenta and Corteva corn herbicides Maize is the same crop as corn, so a maize weeding herbicide is chosen with the tables above: the hybrid's trait, the corn stage and the weeds present. Syngenta's Callisto (mesotrione) is on the list for corn up to V8 or 30 inches, and Syngenta publishes its current label. Read the label of any Syngenta or Corteva corn herbicide for the corn stage and the weed sizes before ordering it. ### Organic corn weed control On an organic farm, a herbicide or any other input must be approved by the certifying agent before use. The [organic input approval checklist](/us/organic-input-approval-checklist/) shows what to ask the certifier. ## Roundup Ready corn and maize: glyphosate-tolerant, LibertyLink and Clearfield hybrids Applying the wrong herbicide to the wrong corn type seriously injures the crop. Check the seed bag or the seed company's documents for the traits of the hybrid you planted, and keep them with your spray records. Glyphosate-tolerant, LibertyLink and Clearfield corn are different systems, so match the trait to the herbicide label. Four types of herbicide-resistant corn are grown in the Pacific Northwest, some genetically engineered and some developed by genetic selection. - Roundup Ready corn is tolerant to glyphosate at labeled rates up to 30 inches tall with eight or fewer collars; Roundup Ready Corn II has elevated tolerance. Glyphosate applied to corn not confirmed tolerant may kill the crop. - LibertyLink corn is tolerant to over-the-top glufosinate products (Liberty, Ignite, Sinate, Rely 280), applied up to 24 inches with seven or fewer collars. Translocation is limited, so weeds must be small. - Clearfield (IMI) corn was developed by genetic selection to tolerate imidazolinone herbicides such as Lightning, Pursuit and Optill. - Poast Protected corn was developed by traditional breeding and selection. Glyphosate is a nonselective, non-residual, translocated herbicide, and glyphosate-resistant kochia is known in eastern Oregon and parts of southwestern Idaho. A Bt trait is a plant-incorporated protectant: a pesticidal substance the plant produces from genetic material. A stacked hybrid carries proteins against two insect groups, or herbicide tolerance plus at least one Bt protein. Note insect traits and herbicide tolerance separately for each hybrid; they answer different questions. Open the [label guide](/us/read-pesticide-label/) with the container beside you and use the exact formulation name and registration number. After a delayed application, look at the weeds again, map surviving patches, photograph representative plants for identification, and plan for later flushes, because the main active ingredients here are non-residual. ### Roundup Ready corn pros and cons The advantage of Roundup Ready corn is that glyphosate can be applied at labeled rates up to 30 inches tall with eight or fewer collars. The drawbacks are that glyphosate is non-residual, that glyphosate applied alone may not control kochia, nightshades, wild buckwheat, horseweed, dandelion or common lambsquarters, and that glyphosate-resistant kochia is known in eastern Oregon and parts of southwestern Idaho. ## Sweet corn herbicide recommendations: weed control in sweet corn, including Round Up Ready sweet corn Keep a sweet corn field weed-free until the plants are at least 24 inches tall. Sweet corn competes well with weeds, and where the infestation is low, cultivation alone can be enough. Pre emergence and post emergence herbicides are available for sweet corn, and the choice depends on the weed problem and the corn growth stage. Round Up Ready sweet corn is a sweet corn hybrid that carries the glyphosate-tolerance trait; the seed company’s trait documents for the hybrid, not the variety name, show whether it does. Glyphosate goes over the top only on a hybrid that carries the trait and only within the label’s limits on corn height and stage, as set out in the Roundup Ready corn section above. Before ordering, check that the product label names sweet corn and the growth stage at which you will spray, and read the hybrid's trait documents as described in the section on herbicide-tolerant corn above. Roundup Ready 2 Technology sweet corn hybrids resist glyphosate after emergence; if non-GMO sweet corn hybrids are planted, the post-applied herbicide options are limited. There are more pre-emergent herbicides available in sweet corn than post-emergent ones, so a pre-emergent product is the more practical base of the program. Hybrids differ in tolerance too: super sweet hybrids are commonly more susceptible to damage from sulfonylurea herbicides such as Accent Q. ### Crabgrass control in sweet corn Many preemergence and postemergence herbicides are available for sweet corn, depending on the weed and the corn stage, so for crabgrass (a grass weed) look for crabgrass in the weed list of the sweet corn label. Keep the field weed-free until the sweet corn is at least 24 inches tall. ### 2,4-D on corn: timing before emergence and on sweet corn 2,4-D, often written 24D, is a group 4 growth regulator that can go on corn before the crop emerges, but the timing is set by the product label. Some labels recommend the spray either 7 to 14 days before planting or 3 to 5 days after planting before the corn has emerged, and others allow it any time after planting. An application around planting can injure corn, more so on coarse soils low in organic matter and when rain and wet soil follow within a week of planting. Amine is more likely to injure corn than ester when applied before emergence, and some labels do not allow preplant or preemergence use on light, sandy soils. For a pre emergent 24D spray, take the interval printed on your product's label first, then your soil type. Spraying 24D on sweet corn follows its own limits. The amine products listed for sweet corn are used at 1 to 2 pt/A, once 7 to 14 days before planting or after planting but before emergence, and once after emergence while the corn is under 8 inches tall, or with drop nozzles when it is taller, up to the dough or denting stage. The pre-harvest interval for sweet corn is 45 days, the yearly maximum is 3.15 pt/A, sandy soil is excluded, and only the amine formulation is used. Do not cultivate for 7 to 10 days after spraying emerged corn, because stems can break. Check the label for the growth stage you will be in on the spray day, and record the product, rate and corn stage in the spray log. ## Best herbicide for volunteer corn by crop and resistance traits Volunteer corn grows from kernels or ears lost at harvest, which can drop after mechanical harvest problems, insect damage or late-season windstorms; plants left from a failed stand that is replanted also act as volunteers. Herbicide options depend on the resistance traits of the volunteers and on the crop they infest. Start by writing down where the volunteers came from (lost kernels or ears, or a failed stand), which hybrid and traits grew in the field last year, the crop you are protecting, how dense the plants are, whether they stand singly or in clumps, and how tall they are. Clumps compete harder than single plants, so a count that ignores them misses part of the picture. Volunteer corn seeds are non-photoblastic and germinate whether or not they are exposed to light. ### Volunteer corn herbicide in soybeans - Glyphosate does not control glyphosate-resistant volunteer corn. Glufosinate controls volunteer corn unless it is LibertyLink. Glufosinate goes only on LL or RR/LL soybean, at 32–43 fl oz/ac. - Group 1 herbicides (Select Max, Assure II, Fusilade, Poast) are typically very effective over the top in soybean. Quizalofop, fluazifop, sethoxydim and clethodim control volunteer corn regardless of RR, LL or RR/LL traits. - Clethodim control can drop by about 60% in a mixture with glyphosate or glyphosate plus 2,4-D, and by about 75% with glyphosate plus dicamba. A maximum labeled rate or a more aggressive adjuvant minimizes the loss. - For dense clumps, one more cultivation 7–10 days after application, or a second Liberty application 10–21 days after the first. - Contact herbicides leave regrowth when the growing point survives and are ineffective on volunteer corn smaller than V6; spray when plants are 5–12 inches tall. - Paraquat controls volunteer corn that emerged before soybean planting. Clethodim in a burndown goes on at least six days before corn planting. Before tank-mixing, read the exact label and ask whether each partner product lowers grass control. If a mixture gave poor control, check the ingredients, rates, timing and conditions before you spray it again. ### Volunteer corn herbicide in corn A failed stand that you replant is a different job from protecting an established crop, so name the planned planting in your question. Fewer options exist in a corn crop. Where the volunteers are conventional and this year's corn is Roundup Ready, glyphosate is the better option. A failed stand with stacked RR/LL traits can be cleared with clethodim (Select Max) at 6 fl oz/ac plus 2.5 to 4 lb/ac ammonium sulfate, which requires 6 days before corn is replanted; paraquat plus metribuzin avoids that wait. Enlist corn can be sprayed with Assure II (quizalofop), which controls glyphosate- and glufosinate-resistant volunteers. ### Volunteer herbicide label: what to read before you buy A volunteer herbicide label is the label of the product you picked for volunteer corn. The label sets who may use the pesticide and where, how, how much and how often. Read the crop section for your soybean or corn crop: Group 1 products (Select Max, Assure II, Fusilade, Poast) are typically very effective over the top in soybean, and glufosinate goes only on LL or RR/LL soybean at 32–43 fl oz/ac. ### What volunteer corn costs In South Dakota research, soybean yield loss was 8–9% at about one volunteer corn plant per 10 square feet and 71% at about one plant per square foot. Left uncontrolled, 3,500 plants/ac cause a 2% yield loss in corn and 10% in soybean; 7,000 plants/ac cause 5% in corn and 27% in soybean. Clumps are usually more aggressive than single plants. Herbicide antagonism in tank mixes affects volunteer corn management. ### Volunteer corn and rootworm Volunteer corn left to silk attracts rootworm beetles to lay eggs in the soybean field and feeds larvae that hatch there. Eliminate volunteer corn and grassy weeds that can serve as hosts. Treat volunteer control as part of the corn-soybean rotation, and ask how to cut harvest losses that leave ears and kernels in the field. ## Next step Take the hybrid traits, weed species, crop stage and treatment history to your adviser. Check the candidate product against them in the [label guide](/us/read-pesticide-label/).