Sweet Corn (Fresh, Processing, and Seed)

Ed Peachey
Revised March 2014

CORN, SWEET—Preplant Incorporated and Preemergence Surface

acetochlor (Surpass or Cadence)

Rate 0.8 to 3 lb ai/A. Consult appropriate label for rates.

Time Apply preplant or preemergence.

Remarks Use lower rates on coarse soils with low organic matter. May be surface-applied or incorporated into top 1 to 2 inches of soil. If rain or 0.25 to 0.75 inch of overhead irrigation does not occur within 7 days of a surface application, shallowly incorporate herbicide with a rotary hoe or similar device. May tank mix with several other herbicides to broaden activity.

Caution Improper incorporation methods or poor soil preparation may reduce weed control. Consult label for crop rotation restrictions.

Site of action Group 15: inhibits very long chain fatty acid synthesis

Chemical family Chloroacetamide

alachlor (Micro-Tech or several premixes with atrazine)

Rate 2 to 3.5 lb ai/A (2 to 3.5 quarts/A) depending on application timing and soil type

Time Preplant incorporated: apply immediately before planting, and incorporate mechanically in top 1 to 2 inches of soil for furrow-irrigated corn. Preemergence surface: apply after planting and incorporate by cross-harrowing with a spike-tooth harrow; or activate with overhead irrigation.

Remarks Can apply through a center-pivot irrigation system. See label for specific rates, depending on soil texture, organic matter, and possible use of tank-mixes or other herbicide combinations. Controls atrazine-resistant redroot pigweed, nightshade, and purslane. Inhibits roots and shoots.

Caution A restricted-use herbicide due to ground and surface water contamination potential.

Site of action Group 15: inhibits very long chain fatty acid synthesis

Chemical family Chloroacetamide

atrazine (several trade names)

Rate Consult label for yearly changes.

Time Apply preplant or preemergence by selecting rates depending on soil type listed on label.

Remarks Activate with overhead irrigation in 7 days or incorporate mechanically in top 2 inches of soil for rill-irrigated fields east of the Cascades. Control of barnyardgrass and yellow foxtail is poor if the soil surface remains dry or if these grasses grow beyond the two-leaf stage. Do not plant crops other than corn during the season of treatment. Other crops can be planted the next year west of the Cascades, if treated before June 10 with 2 lb/A or less; east of the Cascades, use other herbicides when planting corn the next year.

Caution A restricted-use herbicide. Also, any product or premix containing more than 4% atrazine is restricted use (Atrazine 4L is 42% atrazine). Some populations of redroot pigweed, groundsel, kochia, and lambsquarters have evolved resistance to atrazine. Combine other herbicides with atrazine if these species are present. Do not exceed 2 lbs ai/A for any single application. Do not exceed 2.5 lb ai/A per year. Do not graze treated area or feed treated forage to livestock for 45 days after application. After harvest, plow and thoroughly mix the soil to reduce possible injury. Do not apply through any type of irrigation system.

Site of action Group 5: photosystem II inhibitor

Chemical family Triazine

dimethenamid-P (Outlook)

Rate 0.56 to 0.98 lb ai/A (12 to 21 fl oz/A)

Time Apply preplant incorporated, preplant surface, or preemergence surface.

Remarks Consult label for application rate in relation to soil type. Use lower rates on coarse soils with low organic matter or low cation exchange capacity. Control is best if incorporated into soil by overhead moisture or a light mechanical tillage (1 to 2 inches deep) before weed seedlings emerge. May be tank mixed with other herbicides to improve weed control. Control of wild proso millet can be enhanced if Outlook is applied preemergence after preplant-incorporating Dual Magnum.

Caution Apply through irrigation systems as described on the label. Delayed and erratic emergence or leaf wrapping of sweet corn may occur if conditions are extreme (heavy rain and extended periods of water-saturated soil and/or cool weather) during germination and emergence, particularly for preplant-incorporated applications followed by cool, wet weather. Do not apply on sweet corn grown for seed.

Site of action Group 15: inhibits very long chain fatty acid synthesis

Chemical family Chloroacetamide

mesotrione (Callisto)

Rate 0.078 to 0.094 lb ai/A (2.5 to 3 fl oz/A product)

Time Apply preemergence surface after planting.

Remarks Good control of some broadleaves. Tank mix with atrazine to improve weed control.

Caution Some sweet corn varieties are more sensitive than others. Rotational interval is 18 months for peas, snap beans, cucurbits, beets, and many other crops. Crop yield may be reduced if applied to corn treated with the insecticides Counter or Lorsban. Do not apply more than 0.24 lbs ai/A per year (7.7 fl oz).

Site of action Group 27: inhibits 4-hydroxyphenylpyruvatedioxygenase (4-HPPD)

Chemical family Triketone

pendimethalin (Prowl H2O)

Rate 0.74 to 1.98 lb ai/A (2 to 4 pints/A Prowl H2O) depending on soil texture and organic matter content.

Time Apply preemergence only; do not preplant-incorporate. Apply over a uniform seedbed with corn seed planted 1.5 inches deep to ensure selectivity.

Remarks Note rates listed on label for different soil types and organic-matter contents.

Caution May cause lodging of sweet corn. Planting deeply and hilling during cultivation may help to reduce lodging. Do not incorporate. Use only shallow cultivation to reduce soil mixing at or near seed. Do not apply to reduced-till or no-till corn.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Dinitroaniline

simazine (Princep 4l, Simazine 4L, and others)

Rate 1.6 to 4 lb ai/A (1.6 to 4 quarts/A, depending on product)

Time Preemergence, apply before weeds and corn emerge.

Remarks Maximum rate on highly erodible soils is 1.6 quarts/A if less than 30% of the soil is covered with plant residues. Preharvest and pregrazing interval is 45 days. Can be preplant-incorporated.

Caution A restricted-use herbicide in Washington. Do not plant crops other than corn for 1 year. Do not graze treated areas. Do not exceed 2.5 quarts/A per year. After harvest, plow and thoroughly mix the soil to reduce possible injury.

Site of action Group 5: photosystem II inhibitor

Chemical family Triazine

S-metolachlor (Dual Magnum or Dual II Magnum with corn safener) or metolachlor (Parallel)

Rate Consult labels to adjust rates for soil types and organic matter content.

Time Apply preplant incorporated, preemergence, or early postemergence, before weeds germinate or yellow nutsedge emerges.

Remarks Activate with shallow incorporation or overhead moisture. Dual II has corn safener.

Caution Consult label for specific rates, depending on soil texture and especially organic matter, or for restrictions on planting sensitive crops within 4 to 5 months. Inhibits root and shoot growth.

Site of action Group 15: inhibits very long chain fatty acid synthesis

Chemical family Chloroacetamide

CORN, SWEET—Postemergence for Soil Residual

dimethenamid-P (Outlook)

Rate 0.56 to 0.98 lb ai/A (12 to 21 fl oz /A)

Time Early postemergence on corn up to 12 inches tall.

Remarks Consult label for application rate in relation to soil type. Use lower rates on coarse soils with low organic matter or low cation exchange capacity. May be tank mixed with other herbicides to provide burndown with residual control.

Caution Consult label for instructions on applications made through some irrigation systems. Regional experience indicates that corn may be injured by postemergence applications made during very hot weather. Do not apply on sweet corn grown for seed.

Site of action Group 15: inhibits very long chain fatty acid synthesis

Chemical family Chloroacetamide

pendimethalin (Prowl 3.3 EC or Prowl H2O)

Rate 0.74 to 1.98 lb ai/A (1.8 to 4.8 pints/A Prowl 3.3, or 2 to 4 pints/A Prowl H2O), depending on soil texture and organic matter content

Time Apply to emerged corn until 20 to 24 inches tall or at V8 growth stage, whichever is more restrictive.

Remarks Does not control emerged weeds. Note rates listed on label for different soil types and organic-matter content. Tank mix with other postemergent herbicides to control emerged weeds. Use drop nozzles if the corn canopy intercepts the spray and prevents it from uniformly reaching the soil.

Caution Do not incorporate. Use only shallow cultivation to reduce soil mixing at or near seed.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Dinitroaniline

S-metolachlor (Dual Magnum or Dual II Magnum with corn safener) or metolachlor (Parallel)

Rate Consult labels to adjust rates for soil types and organic matter content.

Time Apply early postemergence before weeds germinate or yellow nutsedge emerges.

Remarks Activate with shallow incorporation or overhead moisture. Dual II has a safener to reduce potential injury. Suppresses yellow nutsedge.

Caution Consult label for specific rates, depending on soil texture and especially organic matter, or for restrictions on planting sensitive crops within 4 to 5 months. Inhibits roots and shoots.

Site of action Group 15: inhibits very long chain fatty acid synthesis

Chemical family Chloroacetamide

CORN, SWEET—Postemergence

2,4-D amine

Rate 0.24 to 0.71 lb ae/A (0.5 to 1.5 pints/A)

Time Apply after corn is tall enough to use drop nozzles between rows.

Remarks To avoid drift injury, use the same precautions in spraying 2,4-D as for winter cereals. Avoid contact with corn foliage to reduce brittle stalks and whorl distortion that prevents tassel emergence. Mimics natural plant hormones.

Caution Do not apply from tasseling to dough stage of corn. Crop injury is more likely if corn is growing rapidly under high temperature and high soil moisture.

Site of action Group 4: synthetic auxin

Chemical family Phenoxy acetic acid

atrazine + crop oil

Rate Consult labels.

Time Apply postemergence before grass weeds exceed 1.5 inches and broadleaf weeds 4 to 6 inches but before corn is 12 inches tall.

Remarks Use lower water carrier volumes to improve activity. Do not exceed 1 to 1.5 lb ai/A when wheat is expected to follow in the rotation. Consult label for replanting sensitive crops within 12 to 24 mo.

Caution A restricted-use herbicide. Also, any product or premix containing more than 4% atrazine is restricted use (Atrazine 4L is 42% atrazine). Do no exceed 2 lbs ai/A for any single application. Do not exceed 2.5 lb ai/A per year. Reduce potential soil residue by keeping applications under 2 lb/A, or select other herbicides.

Site of action Group 5: photosystem II inhibitor

Chemical family s-triazine

bentazon (Basagran)

Rate 0.5 to 1 lb ai/A (1 to 2 pints/A)

Time Apply to small annual broadleaf weeds; see label for maximum weed size.

Remarks Use higher rate with crop oil concentrate applied twice, 7 to 10 days apart, for Canada thistle and yellow nutsedge. Irrigate before application to ensure vigorous weed growth. Control is poor if day and night temperatures are below 75°F and 55°F, respectively. Use at least 5 gal/A water and at least 40 psi to ensure thorough coverage of weed foliage. Corn leaves may be speckled temporarily, but plants continue growth without further symptoms within 10 days.

Caution Do not apply to corn growing under stress conditions. Do not mix with insecticides. Do not exceed 2 lb ai/A per season.

Site of action Group 6: photosystem II inhibitor

Chemical family Benzothiadiazole

carfentrazone (Aim EC)

Rate 0.008 to 0.016 lb ai/A (0.5 to 1 fl oz/A Aim EC)

Time Apply to actively growing broadleaf weeds up to 4 inches tall or 3 inches across. Apply to corn from before planting up to the 14th collar growth stage, and when weeds are small. Use directed applications if corn is larger than the V-8 stage.

Remarks Adjust nozzles to minimize herbicide application directly over row that might concentrate spray in whorl of corn plant. Acts on contact. Fields can be planted to labeled crops at any time and rotated to any other crop 12 months after application (see label). Good spray coverage is essential.

Caution Avoid applying to corn with collars filled with water. Use only a nonionic surfactant on sweet corn. Avoid any chance of spray drift to non-target sites. User assumes all responsibility for crop loss or damage of sweet corn varieties and inbred lines for seed production. Overlapping applications can injure crop. Tank-mixtures of carfentrazone with emulsifiable concentrate (EC) formulations of other herbicides, fungicides, or insecticides, or with crop oil concentrate, methylated seed oil, or silicone-based adjuvants may increase crop injury. Adding nitrogen or ammonium sulfate with nonionic surfactant may increase leaf injury. Do not exceed 0.031 lb ai/A (2 fl oz/A Aim EC) per season.

Site of action Group 14: inhibits protoporphyrinogen oxidase

Chemical family Triazinone

clopyralid (Stinger)

Rate Apply 0.124 to 0.25 lb ae/A (0.33 to 0.66 pint/A of Stinger) uniformly with ground equipment as a broadcast or directed spray in 10 to 20 gal/A total spray volume.

Time Any time after sweet corn emerges until it is more than 18 inches tall.

Remarks To control Canada thistle, apply when most thistle plants have emerged and thistles are at least 6 to 8 inches wide or tall, but before bud stage. For best results on Canada thistle, use at least 0.5 pint/A product. Do not cultivate before treatment; wait 2 weeks after treatment before cultivation. Re-treat as necessary but do not exceed 0.66 pint/A product per calendar year. Preharvest interval is 30 days for ears and forage, 60 days for stover. Make one to two broadcast applications per crop per year, not to exceed a total of 0.66 pint/A. Re-treatment interval is 21 days. To control Jerusalem artichoke, common cocklebur, jimsonweed, ragweed (common and giant), annual sowthistle, and sunflower, apply Stinger from weed emergence up to the five-leaf growth stage. Use a higher rate listed for heavy infestations, or when greater residual control is desired.

Caution Preharvest interval is 30 days for ears and forage, 60 days for stover. Make one to two broadcast applications per crop per year, not to exceed a total of 0.66 pint/A. Re-treatment interval is 21 days. Do not graze treated areas or harvest corn for feed within 40 days of treatment. Wheat, barley, canola, Brassica crops (including those grown for seed), garden beets, sugar beets, oats, grasses, field corn, spinach, or turnips may be planted any time after treatment. Asparagus, grain sorghum, mint, onion, and strawberries can be planted 12 months after application. Alfalfa, dry bean, soybeans, and sunflowers can be planted 1 month after application if rain (not including irrigation) is greater than 18 inches, or after 18 months if rainfall is less than 18 inches. Do not plant broadleaf crops grown for seed (excluding Brassica seed crops), carrot, celery, lentils, lettuce, melons, peas, potatoes, safflower, or tomato for 18 months after applying clopyralid.

Site of action Group 4: synthetic auxin

Chemical family Pyridine

fluroxypyr (Starane)

Rate 0.125 lb ae/A (0.66 pint/A product)

Time Apply broadcast to actively growing broadleaf weeds before they are 8 inches tall, and up to and including four fully exposed leaf collars (V4 growth stage). After the V5 or V4 stages, apply as a directed spray with drop nozzles.

Remarks Primarily to control volunteer potatoes in sweet corn, but acts on a number of broadleaf weeds.

Caution Not all sweet corn varieties have been screened for tolerance to fluroxypyr, and varieties may differ in their tolerance. Do not allow grazing. Preharvest interval is 47 days for foraging treated field corn, 31 days for sweet corn ears. Do not add a spray adjuvant when applying fluroxypyr alone on sweet corn.

Site of action Group 4: synthetic auxin

Chemical family Pyridine

fluthiacet-methyl (Cadet)

Sweet corn for processing only

Rate 0.004 to 0.006 lb ai/A (0.6 to 0.9 fl oz /A)

Time Apply to corn from two leaf (two leaf collars) to when corn is 48 inches tall or before tasseling, whichever comes first. See label for maximum growth stage and weeds controlled.

Remarks See label for maximum weed size, usually 3 inches or less tall with the exception of velvetleaf (36 in tall). Spray adjuvants are required for optimum weed control. See label for adjuvant recommendations. Thorough coverage is essential for control of susceptible broadleaf weeds. Lower rate can be used if tankmixing with glyphosate for preplant burndown.

Caution Do not exceed 0.009 lb ai/A (1.25 fl oz/A Cadet) per season.

Site of action Group 14: protoporphyrinogen oxidase inhibitor

Chemical family Triazinone

foramsulfuron (Option)

Rate 0.033 to 0.038 lb ai/A (1.5 to 1.75 oz/A product)

Time Apply postemergence up to the V5 stage of development or 16 inches tall. Drop nozzles must be used when corn is beyond the V5 stage, or 16 to 36 inches tall.

Remarks Always use a methylated or ethylated seed oil at 1.5 pints/A, plus UAN (28-0-0 or 32-0-0) at 2 quarts/A. Apply in 10 to 20 gal/A water. Target application timing to annual grasses 1 to 3 inches tall. Option controls nightshade species better than Accent.

Caution Do not rotate to other crops for 60 days after applying. Do not combine with crop oil concentrate or nonionic surfactant. Foramsulfuron, like other sulfonylurea herbicides, may temporarily stunt or yellow corn. Follow seed company recommendation charts for hybrid sensitivity to sulfonylurea herbicides or ALS inhibitors. Do not apply to corn that shows injury from previous applications of other herbicides. Do not apply in the same season with the insecticides Counter 15 G, Counter 20 G, Dyfonate, or Thimet. Do not make foliar applications of an organophosphate insecticide within 7 days of application, or corn may be injured. Do not apply more than twice per season.

Site of action Group 2: acetolactate synthase (ALS) inhibitor

Chemical family Sulfonylurea

halosulfuron-methyl (Sandea)

Rate 0.5 to 0.75 oz ai/A (0.66 to 1 oz/A)

Time Apply postemergence from spike through layby stage.

Remarks Sandea is not recommended for use on “Golden Jubilee.” Avoid concentrating into the plant whorl. Maximum of 0.75 oz ai/A per application on sweet corn and popcorn. Controls only susceptible broadleaf weeds and nutsedge. Nightshades are not controlled. Always add a nonionic surfactant if not tank mixed with other herbicides. Apply only with ground equipment. May apply up to two times during growing season.

Caution Not all varieties have been tested for sensitivity to this herbicide. Before using, consider crop rotation plans. Do not replant or rotate to wheat within 2 months.

Site of action Group 2: acetolactate synthase (ALS) inhibitor

Chemical family Sulfonylurea

mesotrione (Callisto)

Rate 0.078 to 0.094 lb ai/A (2.5 to 3 fl oz/A product)

Time Apply postemergence to corn less than 5 inches tall.

Remarks Good control of some broadleaf weeds, with suppression of wild proso millet. Tank mix with atrazine to improve broadleaf control.

Caution Some sweet corn varieties are much more sensitive to mesotrione than others ( http://horticulture.oregonstate.edu/content/sweet-corn-hybrid-tolerance-... ). Rotation interval is 18 months for peas, snap beans, cucurbits, beets, and many other crops. Crop yield may be reduced if applied to corn treated with the insecticides Counter or Lorsban. See label for adjuvant restrictions for sweet corn, which recommends nonionic surfactant rather than crop oil concentrate, particularly under lush growing conditions. Do not add UAN or AMS. Do not apply more than 0.24 lbs ai/A per year (7.7 fl oz).

Site of action Group 27: inhibits 4-hydroxyphenylpyruvatedioxygenase (4-HPPD)

Chemical family Triketone

nicosulfuron (Accent, Accent Q)

Rate 0.24 to 1.0 oz ai/A (0.33 to 1.33 oz/A)

Time Apply to actively growing weeds, either broadcast before corn is at fourth-collar stage (see label for definition) or with drop nozzles according to label instructions.

Remarks See label for details, application restrictions, and ways to minimize potential crop injury. Applying 0.66 oz/A generally is sufficient to control wild proso millet without undue risk of injuring sweet corn. In recent research, tank-mixes of Outlook and/or Lorsban or other insecticides caused severe injury. Adjuvants improve uptake into leaves. Sweet corn variety tolerance to both Accent and Callisto herbicides can be found online at http://horticulture.oregonstate.edu/content/sweet-corn-hybrid-tolerance-... . Accent Q includes the safener isoxadifen.

Caution Avoid repeat applications in the same field, to minimize selection for resistant weed biotypes. Do not apply as a tank-mix with Basagran (bentazon), as serious injury will result. Do not apply when the difference between the daytime high and the nighttime low temperature is expected to be 35°F or greater. Note especially precautions about types and timings of insecticide applications and environmental conditions that stress corn growth or reduce corn metabolism of nicosulfuron. Do not graze livestock or feed any treated component within 30 days of application. Read and understand product label thoroughly before treating sweet corn.

Site of action Group 2: acetolactate synthase (ALS) inhibitor

Chemical family Sulfonylurea

paraquat (Gramoxone Max or Firestorm)

Rate Consult labels.

Time Apply postemergence as a directed spray when corn is at least 10 inches tall. Use nozzles arranged to spray no higher than the lower 3 inches of corn stalks. Add a nonionic surfactant or crop oil concentrate according to label specifications, taking care to avoid anionic formulations that react in the tank to form insoluble precipitates.

Caution A restricted-use herbicide. Do not ingest or inhale spray mist. Wear protective face shields, respirators, and clothing.

Site of action Group 22: photosystem I electron diversion.

Chemical family Bipyridilium

tembotrione (Laudis)

Rate 0.082 lb ai/A (3 oz product/A)

Time Apply to actively growing weeds from emergence to the V8 stage of growth, or sweet corn up to the V7 stage of growth.

Remarks One application per season on sweet corn. Consult label for maximum weed size. Use methylated seed oil (MSO) at 1% v/v plus ammonium nitrogen fertilizer (UAN) at 1.5 quarts/A or 1.5 lb/A spray-grade ammonium sulfate (AMS) when tembotrione is used alone, or when a specific adjuvant is not specified on the label. Adding atrazine at 1 pint/A significantly broadens the spectrum of control. Tank-mixes with residual herbicides such as S-metolachlor (Dual Magnum) and dimethenamid-P (Outlook) will improve long-term control but may increase potential of crop injury. Potential injury from these tank-mixes can be minimized by applying after V4 stage of corn growth, by eliminating UAN from the tank-mix, or avoiding application after cool and wet weather.

Caution Not all hybrids of corn have been tested for herbicide tolerance. The variety Captain appears to more sensitive that other corn varieties to tembotrione. New varieties should be screened for tolerance to tembotrione on small areas of fields. Weed control may be reduced if applied to stressed weeds or weeds covered by dust or heavy dew. Do not graze livestock or harvest for forage within 45 days after application. Note crop rotation restrictions on label.

Site of action Group 27: inhibits 4-hydroxyphenylpyruvatedioxygenase (4-HPPD)

Chemical family Triketone

topramezone (Impact)

Rate 0.0164 to 0.218 lb ai/A (0.75 to 1 oz/A)

Time Apply postemergence to actively growing weeds 3 to 8 inches tall.

Remarks Controls wild proso millet, several other annual grasses, and many annual broadleaf weeds. A supplemental label for Oregon, Washington, and Idaho allows for up to 1 oz/A in single or sequential applications. See label for optimal treatment time for weeds of different sizes. Add methylated seed oil or crop oil concentrate at 1 to 1.5% v/v and UAN or ammonium phosphate at 1.2 to 1.5% v/v to the spray solution. Spray-grade ammonium sulfate at 8.5 lb/100 gal of water may be substituted for the nitrogen fertilizers. For best performance, tank mix topramezone with 0.25 to 1 lb ai/A of atrazine. Topramezone may be used sequentially or in combination with all soil- or foliar-applied insecticides registered for use in corn. Tank-mixes with residual herbicides such as S-metolachlor (Dual Magnum) and dimethenamid-P (Outlook) will improve long-term control but may injure the crop. Potential injury from these tank-mixes can be minimized by applying after the V4-6 stage of corn growth, by eliminating UAN from the tank-mix, or avoiding application after extended periods of cool and wet weather

Caution Apply only once per growing season. Preharvest interval is 45 days. See label (and supplemental label) for Oregon, Washington, and Idaho rotational crop restrictions. Has not been tested on all sweet corn lines for tolerance.

Site of action Group 27: inhibits 4-hydroxyphenylpyruvatedioxygenase (4-HPPD)

Chemical family Triketone

CORN, SWEET—Quackgrass and Other Perennial Grasses

atrazine

Rate Consult label

Time Apply in fall or, preferably spring either as a single application at higher rates 1 to 3 weeks before plowing to actively growing quackgrass or as a split treatment, first before plowing and second before, during, or after planting, before weeds are 1.5 inches tall.

Remarks Adding a nonionic adjuvant enhances control. Control of wild proso millet is poor. See label for planting sensitive crops within 12 to 24 months, depending on time of application and total applied. Select other herbicides with reduced soil persistence to reduce carryover.

Caution A restricted-use herbicide. Do not graze treated area or feed treated foliage to livestock for 45 days after treatment.

Site of action Group 5: photosystem II inhibitor

Chemical family Triazine

glyphosate (numerous trade names)

Rate Consult labels.

Time Spot-treat vigorously growing quackgrass 6 to 8 inches tall by eliminating both the weed and crop within the treated area.

Remarks Spray before corn silks to avoid residues in the harvested crop. Inhibits production of three amino acids and protein synthesis.

Caution Do not treat more than 10% of the acreage.

Site of action Group 9: inhibits EPSP synthase

Chemical family None generally accepted

sethoxydim (Poast)

Poast-protected sweet corn varieties only

Rate Consult label; maximum rate is 0.28 lb ai/A (1.5 pints/A) with a maximum of 0.56 lb ai/A (3 pints/A) per year).

Time Maximum height for quackgrass and wild proso millet control is 8 and 10 inches, respectively.

Remarks Use in Poast-protected sweet corn varieties only, such as Rogers GH 2042, GH 6333, and GH 6631. May be applied over the top. A second application is allowed 10 days after the first. Identify susceptible grasses and add 2 pints/A nonphytotoxic crop oil concentrate to improve leaf absorption. Control often is erratic on grasses stunted or stressed from drought, high temperatures, or low fertility. Resistant grasses include annual bluegrass and all fine fescues; quackgrass can be suppressed. Grass control may be reduced if applied with bentazon. Inhibits fatty acid production, cell membranes, and new growth.

Caution Do not apply to corn hybrids that are not tolerant to Poast. Do not exceed 3 pints/A per year. Preharvest interval is 60 days.

Site of action Group 1: acetyl CoA carboxylase (ACCase) inhibitor

Chemical family Cyclohexanedione

CORN, SWEET—Wild Proso Millet Control

Biology and management Wild proso millet mimics sweet corn growth. Seeds mature before corn harvest, facilitating spread with machinery. Seed longevity in soil, however, is relatively short (3 to 5 years). Rotating to grass seed or summer annual broadleaf crops helps deplete the seedbank if wild proso millet is not allowed to produce seed. Wild proso millet seedlings emerge erratically throughout the season because of inherent seed dormancy, which is strongest for black-seed types. Cultivation that brings new seeds to the surface, or irrigation and rain, often cause a new crop of weed seedlings to emerge.

Selective herbicides that suppress or control wild proso millet include S-metolachlor, dimethenamid-P, nicosulfuron, and topramezone and tembotrione. In fields with a very high density of wild proso millet seeds, control efforts may need a preplant herbicide such as dimethenamid-P + S-metolachlor, followed by a preemergence herbicide, followed by cultivation(s) or another postemergence herbicide. Both topramezone and tembotrione provide good control of wild proso millet up to 6 inches tall, but do not provide residual control.

CORN, SWEET—Yellow Nutsedge Control

atrazine

Rate Consult label.

Time Apply as a single application or split applications according to one of six alternative methods listed on label.

Remarks Yearly applications or use of other herbicides can reduce populations if a few plants survive growing season.

Caution A restricted-use herbicide. Consult label for planting sensitive crops within 12 to 24 months, depending on time of application and total amount applied.

Site of action Group 5: photosystem II inhibitor

Chemical family Triazine

bentazon

See Corn, Sweet—Postemergence in this section of this handbook. (Controls tubers in Oregon with split treatments applied in warm weather.)

halosulfuron-methyl (Sandea)

Rate 0.5 to 0.75 oz ai/A (0.66 to 1 oz/A)

Time Apply postemergence from spike through layby stage of corn.

Remarks Nutsedge control if applied when nutsedge is in 3- to 5-leaf stage. May need sequential applications with high densities of nutsedge. Apply up to two times during growing season. Always add a nonionic surfactant if not tank mixed with other herbicides. Use drop nozzles to reduce potential injury to corn, especially with sequential applications.

Caution Not all varieties have been tested for sensitivity to halosulfuron. Not recommended on Jubilee.

mesotrione (Callisto)

Rate 0.078 to 0.094 lb ai/A (2.5 to 3 fl oz/A product)

Time Apply postemergence to corn less than 5 inches tall.

Remarks Suppresses nutsedge growth.

S-metolachlor

See Corn—Preemergence, Soil-applied in in this section of this handbook. (Applications inhibit new tuber formation and reduce infestations).

CORN, SWEET—Canada Thistle Control

2,4-D

See Corn, Sweet—Postemergence in this section of this handbook.

bentazon

See Corn, Sweet—Postemergence in this section of this handbook.

clopyralid (Stinger)

See Corn, Sweet—Postemergence in this section of this handbook

Rate Apply 0.124 to 0.25 lb ae/A (0.33 to 0.66 pint/A of Stinger)

Time Any time after sweet corn emerges until it is more than 18 inches tall.

Remarks To control Canada thistle, apply when most thistle plants have emerged and thistles are at least 6 to 8 inches wide or tall, but before bud stage. For best results on Canada thistle, use at least 0.5 pint/A product. Do not cultivate before treatment; wait two weeks after treatment before cultivation. Re-treat as necessary but do not exceed 0.66 pint/A product per calendar year.

Caution Note crop rotation restrictions.

Site of action Group 4: synthetic auxin

Chemical family Pyridine

glyphosate (numerous product names)

Rate Consult labels.

Time Apply at late-bud to early-bloom stage of thistle, but before corn silking.

Remarks Spot-spray thistle patches, eliminating weed and crop in the treated area. Spray before corn silking to avoid residue in harvested crop. Inhibits production of three amino acids and protein synthesis.

Caution Do not treat more than 10% of the acreage.

Site of action Group 9: inhibits EPSP synthase

Chemical family None generally accepted

Herbicide Effectiveness in Sweet Corn

Preplant incorporated or preemergence

Postemergence

Weeds

atrazine(Atrazine)1

mesotrione (Callisto)

S-metolachlor

(Dual II Magnum or

Dual Magnum)

dimethenamid-P

(Outlook)

pendimethalin

(Prowl)2

nicosulfuron

(Accent)3

carfentrazone

(Aim)4

atrazine

(Atrazine)5

bentazon

(Basagran)7

mesotrione

(Callisto)

tembotrione

(Laudis)

topramezone

(Impact)

2,4-D6

E = Excellent G = Good F = Fair P = Poor VP = Very poor or no effect

1 Depends on level of triazine resistance

2 May cause corn to lodge

3 Do not use with organophosphate insecticides

4 Must be applied to small seedlings for good effectiveness

5 Must be applied with crop oil concentrate to small weeds

6 Must be directed to prevent corn injury

7 Good control with two applications 10 days apart

Annual Grasses

Wild proso millet (Panicum miliaceum)

P

P

F

G

G

G-E

VP

P

VP

P

E

E

VP

Barnyardgrass (Echinochloa crus-galli)

F

P

G

E

G

G

VP

G

VP

P

E

E

VP

Witchgrass (Panicum capillare)

P

P

E

E

G-E

G

P

P

VP

P

G

G

VP

Broadleaves

Pigweed (Amaranthus spp.)

F-E

G

G

G

G

G

G

F-E

G

G

E

E

G

Lambsquarters (Chenopodium spp.)

E

G

F

P

G

P

G

E

E

G

E

E

F

Nightshade (Solanum spp.)

G

G

F

G

P

VP

G

G

G

G

E

E

F

Smartweed (Polygonum punctatum)

G

G

P

F

F

P

G

G

E

G

E

E

F

Purslane (Portulaca oleracea)

G

G

F

G

G

P

F

G

P

G

P

F

P

Perennials

Yellow nutsedge (Cyperus esculentus)

F

P

G

G

P

F

VP

F

F

F-G

P

VP

VP

Canada thistle (Cirsium arvense)

P

P

VP

VP

P

F

VP

F

F-G

VP

P

P

F

Quackgrass (Elytrigia repens)

F

P

VP

P

P

G

VP

F

VP

VP

VP

VP

VP