Corn (Field, Sweet, Silage, and Seed Corn)
Bob Parker
Revised October 31, 2008
Herbicide-resistant Corn
Over the past few years, herbicide-resistant field corn has been planted in the Pacific Northwest. The following discussion of herbicide-resistant corn is adapted from North Dakota Weed Control Guide, Publication W-253 (2008, North Dakota State University Extension). Refer to the appropriate herbicide label for guidelines on how to use each product on herbicide-resistant corn. 
CLEARFIELD Corn
Lightning (imazethapyr + imazapyr) controls nearly all annual grass and broadleaf weeds (except ALS-resistant kochia) and suppresses quackgrass and Canada thistle. Apply Lightning only to Clearfield corn varieties and to weeds 1 to 3 inches tall. Apply with oil adjuvant and liquid fertilizer. Lightning contains Pursuit and Arsenal, both imidazolinone herbicides. The rate of Pursuit in Lightning is approximately 1.08 oz/A WDG (water-dispersible granular); Arsenal is at 1% the rate of Arsenal that is registered on noncropland. Refer to the rotational crop restriction on the label. 
LibertyLink Corn
Ignite 280SL (glufosinate), applied postemergence to LibertyLink corn varieties up to 24 inches with seven or fewer collars, controls most annual broadleaf weeds, controls or suppresses grasses, and may suppress some perennial weeds. Apply Ignite 280SL only to LibertyLink corn varieties. Ignite is a nonselective, nonresidual, contact herbicide. Apply when weeds are small because translocation is limited. Ignite does not control large or well-tillered grasses such as yellow foxtail, wild oat, or volunteer cereals. Ignite is nonresidual; controlling multiple weed flushes may require multiple applications or applying with a residual herbicide. Apply with AMS fertilizer. Refer to label for weeds controlled, application information and timing, tank-mix options, and restrictions. Ignite can be used to control weeds resistant to other herbicides. 
Roundup Ready Corn
Glyphosate at labeled rates in Roundup Ready (RR) corn up to 30 inches tall with eight or fewer collars will control most annual and perennial weeds. Apply glyphosate only to RR corn varieties. Certain formulations do not require additional nonionic surfactant, while others require either partial or full nonionic surfactant rates. Add ammonium sulfate to all glyphosate formulations at 2 to 6 lb/100 gal water or at 1 lb/A if applied at less than 12 gal/A. In-crop application timing may not be appropriate for effective perennial weed control. Glyphosate is a nonselective, nonresidual, translocated herbicide that controls grasses and broadleaf weeds. However, glyphosate may not control some broadleaf weeds such as kochia, nightshade, wild buckwheat, horseweed (marestail), dandelion, and lambsquarters if applied alone or after one application. 
Roundup Ready Corn II
Roundup Ready Corn II hybrids have increased resistance to glyphosate compared to RR corn hybrids. Not all glyphosate formulations contain use information on RR Corn II. Glyphosate brands allowing application on RR corn II should be applied to RR corn up to 30 inches or eight collars. Do not exceed 0.75 lb ae/A in a single application. Glyphosate brands registered for RR corn II can be applied to RR corn up to 24 inches or eight collars, or by drop nozzle to corn from 24 to 48 inches; do not exceed 0.75 lb ae/A in a single application to annual weeds or exceed 1.125 lb ae/A to perennial weeds. Generic glyphosate brands can be used on RR corn II hybrids, but follow application information and restrictions on the label. Use glyphosate according to label directions on the glyphosate brand used and not according to the label on a different glyphosate brand. Glyphosate is nonresidual so multiple applications or combining with a residual herbicide may be needed to control multiple weed flushes. Refer to label for weeds controlled, application information and timing, tank-mix options, and restrictions.
CORN—Preplant Incorporated or Preemergence
•  atrazine (several trade names)
Rate  1.6 to 2 lb ai/A
Time  Apply preplant, preemergence, or postemergence when weeds are less than 1.5 inches tall.
Remarks  Use lower rate on coarse soils (sand, sandy loams), higher rate on fine soils (silt loam, clays, silts) and soils high in organic matter. Overhead moisture required for maximum activity. East of Cascades, postemergence applications may be made under sprinkler irrigation. Emerged annual grasses, such as barnyardgrass and green foxtail, are not adequately controlled when soil surface is dry at application and/or grasses are past the two-leaf stage. East of Cascades, where rill irrigated, incorporate 2 inches deep before planting. If applying postemergence, control is enhanced by adding a nonionic adjuvant to the mix.
Caution  A restricted-use herbicide. Plant only corn during the season of treatment. West of the Cascades, crops other than corn can be planted the year after treatment at 2 lb ai/A or less. East of the Cascades, do not plant any crop other than corn the year after treatment. Some populations of redroot pigweed, groundsel, kochia, and lambsquarters have developed resistance to atrazine. Combine other herbicides with atrazine if these species are present. Do not graze treated area or feed treated forage to livestock for 21 days after application. After harvesting a treated crop, plow and thoroughly till the soil in the fall or spring to minimize possible injury to rotational spring-seeded crops.
Site of action  Group 5: photosystem II inhibitor
Chemical family  Triazine
•  alachlor (Bullet, Lariat, or Micro-Tech)
Rate  2 to 4 lb ai/A
Time  Apply either preplant or preemergence.
Remarks  Apply lower rates on coarse soils with low organic matter. See label for rate. If applied preplant, incorporate 2 to 3 inches deep or to moist soil by cross-disking. If applied after planting but before corn emerges, incorporate shallowly in moist soil by cross-spiketooth harrowing. Sprinkler irrigation may be substituted for mechanical incorporation, and herbicide treatment should be made immediately after planting. May be combined with atrazine or cyanazine for better control of broadleaf weeds. Controls atrazine-resistant redroot pigweed, nightshade, and purslane. May be applied through center pivot irrigation systems.
Caution  A restricted-use herbicide. Improper incorporation methods or poor soil preparation will result in reduced weed control.
Site of action  Group 15: inhibits very long chain fatty acid synthesis
Chemical family  Chloroacetamide
•  S-metolachlor (Dual II Magnum or Dual Magnum)
Rate  0.95 to 2 lb ai/A (1 to 2 pints/A Dual II Magnum or Dual Magnum)
Time  Apply either preplant incorporated or preemergence.
Remarks  Use preplant incorporated if furrow irrigated and incorporate into the top 2 inches of soil before planting. Use lower rate on coarse soils, higher rate on fine soils. Preemergence treatment may be used when overhead moisture is expected and should be applied before weeds and corn emerge. May be combined with atrazine to better control broadleaf weeds.
Caution  If crop treated only with S-metolachlor is lost, corn, soybeans, potatoes, safflower, and labeled pod crops can be replanted immediately. Small grains can be planted 4.5 mo after application. Consult label for other crop rotation restrictions.
Site of action  Group 15: inhibits very long chain fatty acid synthesis
Chemical family  Chloroacetamide
•  butylate with safener (Sutan +) 
do not use on corn seed stock
Rate  4 to 6 lb ai/A
Time  Apply preplant within 2 weeks of planting. Incorporate immediately and thoroughly.
Remarks  Soil should have adequate, uniform moisture for good germination but be dry enough to permit herbicide incorporation. Incorporate immediately after applying; either disk in two directions or rototill into top 2 to 3 inches of soil. Higher rates can be used to suppress yellow nutsedge and some perennial grasses.
Caution  Use only on mineral soils with less than 10% organic matter. Do not plant corn seed more than 2 inches deep. Improper incorporation or poor soil preparation results in poor weed control. May injure corn growing under conditions such as extended, unusually cold and wet or hot and dry weather or attacks from insects or diseases. For broadleaf control, combine butylate with a broadleaf herbicide such as atrazine.
Site of action  Group 8: lipid synthesis inhibitor but not an ACCase inhibitor
Chemical family  Thiocarbamate
•  EPTC with safener (Eradicane) 
do not use on corn seed stock
Rate  3.14 to 6.14 lb ai/A
Time  Apply preplant within 14 days of planting; incorporate immediately and thoroughly. Or surface apply immediately after planting and incorporate with 0.5 to 0.75 inch overhead irrigation.
Remarks  Use higher rates to suppress yellow nutsedge and some perennial grasses. Soil should have adequate moisture for good germination but be dry enough to incorporate the herbicide. Incorporate immediately after applying, either by disking in two directions or by rototilling into top 2 to 3 inches of soil. Or, if surface applied, incorporate with a center pivot sprinkler.
Caution  Do not plant corn seed more than 2 inches deep. Use only on mineral soils with less than 10% organic matter. Improper incorporation or poor soil preparation results in poor weed control. EPTC with safener may injure corn under conditions such as extended cold, wet, hot, or dry weather, insect attack, or plant disease. For broadleaf control, combine chemical with a broadleaf herbicide such as atrazine.
Site of action  Group 8: lipid synthesis inhibitor but not an ACCase inhibitor
Chemical family  Thiocarbamate
•  dimethenamid (Frontier) or
•  dimethenamid-P (Outlook)
Rate  0.76 to 1.46 lb ai/A (Frontier) or 0.47 to 0.98 lb ai/A (Outlook)
Time  Apply preplant or preemergence.
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 (CEC). Control is best when applied and incorporated into soil by overhead moisture or a light mechanical tillage before weed seedlings emerge. Till 1 to 2 inches deep to incorporate. May be tank-mixed with atrazine or pendimethalin to improve broadleaf weed control.
Caution  May be applied through certain types of irrigation systems. Delayed emergence or leaf wrapping of sweet corn may occur under extreme conditions of high rain with extended periods of water-saturated soil and/or cool weather during sweet corn germination and emergence. Do not apply on sweet corn grown for seed. Poor soil preparation or improper herbicide incorporation reduces weed control.
Site of action  Group 15: inhibits very long chain fatty acid synthesis
Chemical family  Chloroacetamide
•  pendimethalin (Prowl)
field corn and sweet corn only
Rate  0.75 to 2 lb ai/A
Time  Apply after planting but before crop or weeds emerge.
Remarks  Rate depends on soil type and organic matter content. Plant in a seedbed that is firm and free of clods and trash. Plant at least 1.5 inches deep to ensure good seed coverage. See label for tank-mix combinations. Weed control is best when adequate rain or overhead irrigation is received within 7 days after application.
Caution  Do not incorporate; serious corn injury can result. Do not use on peat or muck soil.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  acetochlor (Harness, Surpass, or Cadence)
consult label for corn uses or types
Rate  0.8 to 3 lb ai/A. Consult appropriate label for rates.
Time  Apply preplant or preemergence.
Remarks  Labels for the products differ. Follow the label for the product being used. 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 be tank-mixed 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
•  mesotrione (Callisto)
do not use on white popcorn
Rate  0.188 to 0.24 lb ai/A (6 to 7.7 oz/A product)
Time  Apply preemergence.
Remarks  Controls several annual broadleaf weeds. If overhead moisture (0.25 inch) is not received within 7 to 10 days after application, rotary hoe to activate the herbicide. Will not control most grass weeds. May be tank-mixed with preemergence grass herbicides to broaden activity.
Caution  Do not exceed 0.24 lb ai/A (7 oz/A product) per season. See label for crop rotation restrictions.
Site of action  Group 28: inhibits 4-hydroxyphenylpyruvatedioxygenase (4-HPPD)
Chemical family  Triketone
•  rimsulfuron (Resolve)
field corn only
Rate  0.5 to 2 oz/A product
Time  Apply preplant or preemergence.
Remarks  Check label for rates for each application timing. Apply to field corn hybrids with a relative maturity date of 77 days or more. If weeds are present at time of application, use an appropriate surfactant. Allow at least 3 wk between preemergence and postemergence applications. Rain or sprinkler irrigation enhances control.
Caution  Not all corn hybrids or Hi-Lysine hybrids have been tested for crop safety. Do not exceed 0.5 oz ai/A (2 oz/A product) per year. Consult label for recropping restrictions. Resolve DF may interact with some soil-applied insecticides.
Site of action  Group 2: acetolactate synthase (ALS) inhibitor
Chemical family  Sulfonylurea
breakhere  CORN—Postemergence
•  2,4-D (several trade names)
Rate  0.5 to 1.2 lb ae/A. Consult label, as 2,4-D labels vary in use rates.
Time  Apply when corn is actively growing.
Remarks  Applying without drop nozzles to corn over 8 inches tall may increase lodging and interfere with normal tassel emergence. Use drop nozzles to avoid applying to corn leaves.
Caution  Do not spray corn from tasseling to dough stage. In western Washington, some common annual broadleaf weeds are tolerant to 2,4-D: chickweed, smartweed, black bindweed, knotweed, and redroot pigweed. Consult label for feeding restrictions.
Site of action  Group 4: synthetic auxin
Chemical family  Phenoxy acetic acid
•  glyphosate (several trade names) 
Several field corn varieties have been developed with resistance to glyphosate. Apply glyphosate only to Roundup Ready corn varieties. Refer to the product label for specific use directions.
•  glufosinate (Ignite 280SL, Liberty) 
Several field corn varieties have been developed with resistance to glufosinate. Apply only to LibertyLink corn varieties. Refer to the product label for specific use directions.
•  imazethapyr + imazapyr (Lightning) 
Several field corn varieties have been developed with resistance to Lightning. Apply Lightning only to Clearfield corn varieties. Refer to the product label for specific use directions.
•  dicamba (Banvel, Rifle, or Clarity)
field corn only
Rate  0.25 lb ae/A
Time  Apply when corn is actively growing and seedling weeds are in the four- to six-true-leaf stage of growth.
Remarks  Does not control grass weeds. If grass weeds are present, combine with a grass-killing herbicide. Controls atrazine-resistant pigweed and lambsquarters. Apply before corn is 24 inches tall, especially if it is growing near sensitive crops.
Caution  Do not apply after corn is 3 ft tall or 15 days before tassels emerge, whichever is first. Some varieties of field corn may show temporary injury after application. Do not apply more than once per season. Do not add spray adjuvants to spray mixes containing dicamba. Do not graze or harvest for dairy or beef feed before ensilage stage (milk stage). Do not apply when temperature is expected to exceed 85°F.
Site of action  Group 4: synthetic auxin
Chemical family  Benzoic acid
•  diflufenzopyr + dicamba (Distinct)
field corn and popcorn only
Rate  0.05 to 0.0785 lb ai/A diflufenzopyr + 0.125 to 0.1875 lb ai/A dicamba (4 to 6 oz/A product) 
Time  Apply 6 oz/A product to corn 4 to 10 inches tall, 4 oz/A product to corn 10 to 24 inches tall.
Remarks  Add a nonionic surfactant at 1 quart/100 gal spray mix plus 5 quarts of urea ammonium nitrate (UAN) per 100 gal spray mix. Spray-grade ammonium sulfate may be substituted for UAN at 17 lb/100 gal spray mix. Distinct applications can be split; allow at least 15 days between applications. Verify selectivity on the popcorn hybrid with your local seed corn company before using. Crop may be temporarily injured if crop is stressed or rapidly growing. Enhance grass control with preemergence grass herbicides or by tank-mixing with nicosulfuron (Accent)
Caution  Do not exceed 10 oz/A product per year. Do not use penetrants such as petroleum-based oils or methylated seed oils; crop may be injured. Distinct is not recommended for use in tank-mixes with plant-growth-regulating herbicides such as 2,4-D, dicamba, or clopyralid unless applications are at least 15 days apart. Preharvest interval is 32 days for silage, 72 days for grain and stover. Do not plant any crop other than corn for 120 days after application.
Site of action  (diflufenzopyr) Group 4: synthetic auxin; (dicamba) Group 19: inhibits indole acetic acid transport
Chemical family  (diflufenzopyr) semicarbazone; (dicamba) benzoic acid
•  bromoxynil (Buctril)
field corn and popcorn only
Rate  0.25 to 0.375 lb ai/A. Up to 0.5 lb ai/A can be used if applied in sprinkler irrigation systems.
Time  Apply after corn reaches the three-leaf (0.25 lb ai/A) or four-leaf (0.375 lb ai/A) stage. See labels for weed-size restrictions.
Remarks  Label rates for each product differ; see appropriate label for maximum rate. Use drop nozzles when corn is more than 8 inches tall. Spray when corn foliage is dry to decrease chance of temporary leaf burn. Warm temperatures also increase chance of some foliage burn. Thorough coverage of weed foliage required for adequate control. Buctril is registered for use for application through sprinkler systems; consult labels for use restrictions.
Caution  Do not cut for feed or graze within 30 days after treatment. Do not plant rotation crop until the following season. Do not add any spray additive or mix with liquid fertilizers.
Site of action  Group 6: photosystem II inhibitor
Chemical family  Nitrile
•  pendimethalin (Prowl)
field corn and sweet corn only
Rate  0.75 to 2 lb ai/A, depending on soil type and percentage of organic matter
Time  Apply when corn has two to four leaves (depending on the tank-mix partner) and when weeds are no more than 2 inches tall.
Remarks  Do not apply Prowl alone postemergence. Consult the label for tank-mix combinations and restrictions. Weed control is best when adequate rain or overhead irrigation is received within 7 days after application. For maximum effectiveness, wait at least 7 to 10 days before cultivating early postemergence treatments.
Caution  May increase lodging of sweet corn. Do not use on peat or muck soils or apply in liquid fertilizer. Do not incorporate.
Site of action  Group 3: microtubule assembly inhibitor
Chemical family  Dinitroaniline
•  clopyralid (Stinger or Clopyr Ag)
Rate  0.063 to 0.25 lb ae/A (0.25 to 0.66 pint/A product) 
Time  Apply to actively growing broadleaf weeds after corn emerges up to 24 inches tall. For Canada thistle, apply after most basal leaves emerge but before bud stage.
Remarks  Clopyr Ag does not have a supplemental label for sweet corn. For best results on Canada thistle, use at least 0.5 pint/A product. Do not cultivate before treatment, wait 2 wk after treatment before cultivation. Re-treat as necessary but do not exceed 0.66 pint/A product per calendar year.
Caution  Do not graze treated areas or harvest corn for feed within 40 days of treatment. Wheat, barley, oats, grasses, field corn, or sugar beets may be planted any time after treatment.
Do not plant alfalfa, asparagus, canola (rapeseed), Brassica species grown for seed, cole crops, dry beans, soybeans, grain sorghum, mint, onions, popcorn, safflower, sunflower, sweet corn, or strawberries during the first 12 mo after applying product.
If annual precipitation (not including irrigation) is 18 inches or more—alfalfa, asparagus, dry beans, canola (rapeseed), Brassica species grown for seed, grain sorghum, mint, onions, popcorn, sweet corn, soybeans, strawberries, and sunflowers may be planted 12 mo after applying product. Cole crops, lentils, peas, potatoes (including potatoes grown for seed), safflower, or broadleaf crops grown for seed (excluding Brassica species) may also be planted 12 mo after treatment; however, unless risk of injury is acceptable, these crops should not be planted until 18 mo after treatment.
If average annual precipitation (not including irrigation) is less than 18 inches—alfalfa, dry beans, soybeans, sunflowers, lentils, peas, potatoes (including potatoes grown for seed), or broadleaf crops grown for seed (excluding Brassica species) should not be planted until 18 mo after applying product. However, crop injury and/or yield loss may occur up to 4 yr after application.
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. Field corn can be treated broadcast up to and including five fully exposed leaf collars (V5 growth stage). Sweet corn can be treated up to and including four fully exposed leaf collars (V4 growth stage). Applications after the V5 or V4 stages should be as a directed spray with drop nozzles.
Remarks  In field corn, a high-quality adjuvant labeled for use on growing crops is recommended to improve weed control. May be applied preplant to control emerged volunteer potatoes. To control heavy populations of volunteer potatoes, a second application may be made postemergence. Only weeds emerged at the time of application will be controlled.
Caution  Do not exceed 0.28 lb ae/A (1.33 pints/A) per growing season. Preharvest interval is 47 days for grazing and forage, 31 days for sweet corn, 90 days for field corn grain and stover. Not all sweet corn hybrids have been screened for tolerance. Crop may be injured when applied as a broadcast treatment to some corn hybrids or lines. Hybrids or lines susceptible to phenoxy injury also may be susceptible to injury from fluroxypyr. Adding a spray adjuvant is not recommended when applying fluroxypyr alone on sweet corn.
Site of action  Group 4: synthetic auxin
Chemical family  Pyridine
•  nicosulfuron (Accent) 
Rate  0.5 oz ai/A (0.67 oz/A Accent)
Time  Apply to corn before the 10-collar growth stage or before field corn is taller than 36 inches, or before seed corn or popcorn is 20 inches tall, or before sweet corn is 18 inches tall, and while weeds are actively growing and in the height range on label.
Remarks  Accent can be used only on certain sweet corn varieties grown for processing; consult label. Special local needs labels ID-960009, OR-960029, and WA-960023. When not tank-mixed with other herbicides, always add a nonionic surfactant or crop oil concentrate to the spray mixture. Consult the label for surfactant or crop oil specification and rates to be used alone or in tank-mixes. Apply only with ground equipment to corn that is not stressed or damaged. Use drop nozzles when field corn is over 24 inches tall or when sweet corn is 12 inches or taller. Check with seed supplier to determine crop tolerance before using on popcorn or corn grown for seed.
Caution  Before using, consider crop rotation plans. Rotation crops other than corn may be very sensitive to low concentrations of nicosulfuron in soil. To avoid injury, do not apply to corn previously treated with Counter or organophosphate soil-applied insecticides such as Thimet, Dyfonate, or Lorsban. Do not apply to corn treated within 7 days with foliar-applied organophosphate insecticides such as Lorsban, malathion, or parathion, or with Basagran, Laddok, or 2,4-D, and do not apply any of these materials within 3 days after applying nicosulfuron, or crop may be injured. See label for further precautions and restrictions. In furrow-irrigated fields, if at least 0.5 inch of rain falls after application, do not use tail water from the first irrigation to irrigate any crop other than field corn, popcorn, or field corn grown for seed.
Site of action  Group 2: acetolactate synthase (ALS) inhibitor
Chemical family  Sulfonylurea
•  primisulfuron (Beacon)
field corn only
Rate  0.57 oz ai/A (0.76 oz/A product)
Time  When corn is 4 to 20 inches tall and weeds are in height range specified on label.
Remarks  May make a split application. Complete all applications before corn tassels. Overhead irrigation or rain within 4 hr after applying may reduce weed control. If not tank-mixed with other herbicides, always add a nonionic surfactant or crop oil concentrate to spray mixture. See label for surfactant or crop oil specification and rates when used alone or in tank-mixes.
Caution  Before using, consider crop rotation plans. Rotation crops other than corn may be sensitive to low concentrations of primisulfuron remaining in the soil. To avoid crop injury, do not apply to corn previously treated with the insecticide Counter. Do not apply primisulfuron to corn treated within 10 days with organophosphate insecticides such as Thimet, Dyfonate, or Lorsban. Do not apply any of these insecticides within 10 days before or after the herbicide treatment, or crop injury may result. Consult label for further use precautions and restrictions.
Site of action  Group 2: acetolactate synthase (ALS) inhibitor
Chemical family  Sulfonylurea
•  rimsulfuron (Resolve DF or SG)
field corn only
Rate  0.125 to 0.5 oz ai/A (0.5 to 2 oz/A product)
Time  Apply postemergence to corn up to 12 inches tall or six leaf collars but before susceptible weeds reach sizes listed on label. 
Remarks  Check label for rates for time of application. Apply to field corn hybrids with a relative maturity date of 77 days or more. If weeds are present at application, use an appropriate surfactant. Allow at least 3 wk between preemergence and postemergence applications. Rain or sprinkler irrigation will enhance control.
Caution  Do not apply to field corn taller than 12 inches or six collars, whichever is more restrictive. Do not exceed 0.5 oz ai/A (2 oz/A product) per year. Consult label for recropping restrictions. Resolve may interact with some soil-applied insecticides.
Site of action  Group 2: acetolactate synthase (ALS) inhibitor
Chemical family  Sulfonylurea
•  thifensulfuron (Harmony GT XP)
field corn only
Rate  0.083 oz/A product
Time  Apply postemergence to two- to six-leaf field corn (one to five collars, up to 16 inches tall) and after weeds emerge but before susceptible weeds reach the sizes listed on the label.
Remarks  Controls broadleaf weeds. Apply to field corn hybrids with a relative maturity date of 88 days or more. Include an appropriate spray additive and either ammonium nitrate or ammonium sulfate to spray mix.
Caution  Do not apply to field corn taller than 16 inches or five collars, whichever is more restrictive. Do not apply with other corn herbicides unless specified on Harmony GT XP labels or technical bulletins. Preharvest interval is 30 days for grazing or feeding forage or grain from treated crop to livestock. Not all corn hybrids or Hi-Lysine hybrids have been tested for crop safety. Do not apply more than once per season. Harmony GT may interact with some soil-applied insecticides.
Site of action  Group 2: acetolactate synthase (ALS) inhibitor
Chemical family  Sulfonylurea
•  bentazon (Basagran)
Rate  0.75 to 1 lb ai/A
Time  For small annual broadleaf weeds. Refer to label for maximum weed size.
Remarks  Adding oil concentrate generally increases weed control but also may increase corn injury. Irrigate before application to ensure vigorous weed growth. Control is poor if days and nights are below 80°F and 60°F, respectively. Use at least 5 gal/A water and at least 40 psi to ensure thorough coverage of weed foliage. Leaves may speckle temporarily, but plants generally outgrow it within 10 days. Use higher rate with oil concentrate applied twice, 7 to 10 days apart for Canada thistle and yellow nutsedge control.
Caution  Do not apply to corn growing under stress, or mix with other pesticides. Do not exceed 2 lb ai/A per season. Seed corn producers should consult the contracting company regarding tolerance of seed production lines. Do not cultivate 5 days before or after application.
Site of action  Group 6: photosystem II inhibitor
Chemical family  Benzothiadiazole
•  halosulfuron (Sandea)
Rate  0.5 to 1 oz ai/A (0.66 to 1.33 oz/A product)
Time  Apply postemergence from spike through layby stage. 
Remarks  Some sweet corn varieties including 'Golden Jubilee' are sensitive to this herbicide. Do not exceed 0.75 oz ai/A per application on sweet corn and popcorn. Controls only susceptible broadleaf weeds and nutsedge. Always add a nonionic surfactant or crop oil concentrate if not tank-mixed with other herbicides. Apply only with ground equipment. May apply up to twice per growing season.
Caution  Before using, consider crop rotation plans.
Site of action  Group 2: acetolactate synthase (ALS) inhibitor
Chemical family  Sulfonylurea
•  flumiclorac (Resource)
field corn only
Rate  0.027 to 0.054 lb ai/A (4 to 8 fl oz/A product)
Time  Apply to field corn from the two-leaf through the ten-leaf stage. (Determine the leaf stage of corn by counting only those leaves with visible leaf collars.)
Remarks  Controls only actively growing, susceptible broadleaf weeds. Rate is determined by weed species and weed growth stage. Flumiclorac must be applied with a crop oil concentrate or methylated seed oil; the amount of additive is determined by the rates and timing. Adding spray-grade ammonium sulfate at 2 to 2.5 lb/A may enhance weed control.
Caution  Do not use on sweet corn or popcorn. Corn leaves open at time of application may show some spotting and burning. Do not apply when corn and weeds are under stress. Do not apply if rain is expected within 1 hr of application. Preharvest interval is 28 days for grazing animals on green foliage or using as feed.
Site of action  Group 14: protoporphyrinogen oxidase inhibitor
Chemical family  N-phenylphthalimide
•  carfentrazone (Aim)
Rate  0.132 oz ai/A (0.5 fl oz/A Aim EC)
Time  Apply to corn up to the eight-collar growth stage and when weeds are small.
Remarks  See label for maximum weed size. Add 0.25% v/v nonionic surfactant. If corn grows in very dry soil, a sprayable liquid nitrogen fertilizer may be used in addition to the nonionic surfactant. Any crop may be planted 30 days after application except barley, oats, and rye, which can be planted 12 mo after application. Good spray coverage is essential. Adjust sprayer to avoid excess herbicide application over the row and/or into the whorl of the corn plant.
Caution  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.
Site of action  Group 14: protoporphyrinogen oxidase inhibitor
Chemical family  Triazinone
•  mesotrione (Callisto)
do not use on white popcorn
Rate  0.094 lb ai/A (3 oz/A product)
Time  Apply postemergence to actively growing weeds less than 5 inches tall and when corn is in eight-leaf stage of growth or less.
Remarks  Controls several annual broadleaf weeds. For field corn, always add crop oil concentrate to spray solution at 1 gal/100 gal water and 2.5% v/v of a 28% or 32% nitrogen solution or 8.5 lb/A of ammonium sulfate to 100 gal spray solution. In sweet corn and yellow popcorn, do not use ammonium sulfate or urea ammonium nitrate, and use nonionic surfactant instead of crop oil concentrate. Does not adequately control grasses. If corn is stressed it may be bleached temporarily. Wait at least 14 days to reapply.
Caution  Do not use methylated seed oil (MSO or MSO blend adjuvants). Do not exceed 0.24 lb ai/A (7 oz/A product) per season. Do not apply mesotrione to corn treated with the insecticides Counter or Lorsban; crop injury may be severe. Do not apply within 7 days before or after applying an organo-phosphate or carbamate insecticide; injury may occur. See label for crop rotation restrictions.
Site of action  Group 28: inhibits 4-hydroxyphenylpyruvatedioxygenase (4-HPPD)
Chemical family  Triketone
•  foramsulfuron (Option)
Rate  0.022 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 urea ammonium nitrate (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.
Caution  Do not rotate to other crops for 60 days after application. 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
•  topramezone (Impact)
Rate  0.0165 lb ai/A (0.75 oz/A product)
Time  Apply postemergence to actively growing weeds 3 to 8 inches tall. 
Remarks  Controls many annual broadleaf weeds and several annual grasses. See label for optimum treatment time for weeds of different sizes. Add methylated seed oil or crop oil concentrate at 1 to 1.5% v/v and urea ammonium nitrate 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 atrazine.  Topramezone may be used sequentially or in combination with all soil- or foliar-applied insecticides registered for use in corn.
Caution  Do not exceed 0.022 lb ai/A (1 fl oz/A product) per growing season. Preharvest interval is 45 days. See label for rotational crop restrictions. Has not been tested on all sweet corn, popcorn, or seed corn inbred lines for tolerance.
Site of action  Group 28: inhibits 4-hydroxyphenylpyruvatedioxygenase (4-HPPD)
Chemical family  Triketone
•  tembotrione  (Laudis)
Rate  0.082 lb ai/A (3 oz/A product)
Time  Apply to actively growing weeds to field corn or popcorn from emergence to the V8 stage of growth, or to sweet corn up to the V7 stage of growth.
Remarks  Consult label for maximum weed size. Use a methylated seed oil (MSO) when tembotrione is used alone, or when a specific adjuvant is not specified on the label. A second application may be made to field or popcorn 14 days after the first application. 
Caution  Do not exceed a total of 6 fl oz/A of product per growing season. Not all hybrids of corn have been tested for herbicide tolerance. Weed control may be reduced if applied to stressed weeds or weeds that are dust covered or in the presence of a heavy dew. Do not graze livestock or harvest for forage within 45 days after application. Note crop rotation restrictions on the label.
Site of action  Group 27: inhibits 4-hydroxyphenylpyruvatedioxygenase (4-HPPD)
Chemical family  Triketone

CORN—Postemergence Directed Spray
•  paraquat (Gramoxone Max or Gramoxone Inteon)
Rate  Gramoxone Max—0.28 to 0.49 lb ai/A (0.75 to 1.3 pints/A); Gramoxone Inteon—0.5 lb ai/A (1 to 2 pints/A)
Time  Apply when corn is at least 10 inches tall with nozzles arranged to spray no higher than the lower 3 inches of corn stalks.
Remarks  Apply by ground in at least 20 gal/A water, and add a nonionic surfactant or crop oil concentrate.
Caution  A restricted-use herbicide. Corn plants shorter than 10 inches (measured from soil surface to top of whorl) may be injured and not recover.
Site of action  Group 22: photosystem I electron diversion
Chemical family  Bipyridilium
CORN—Perennial Weed Control (Quackgrass, Field Bindweed, Canada Thistle, Johnsongrass, etc.)
•  glyphosate
Rate  2.25 to 3.75 lb ae/A (3 to 5 lb ai/A)
Time  Apply to weeds before crop emergence.
Remarks  Rate depends on species and growth stage as specified on label. Use highest rate on field bindweed. Treat perennial weeds when there is a maximum leaf surface and the weed is growing vigorously. Consult label for interval between application and tillage.
Caution  Do not apply to weeds stressed by drought, weather, or maturity. Rain within 6 hr after applying may reduce effectiveness. Be sure to control weed escapes in following years. Do not use glyphosate in galvanized or mild steel tanks. Do not feed or forage treated vegetation within 8 wk of application. Do not apply glyphosate with aerial equipment. Do not mix with other pesticides or herbicidal oils unless specified on label. For best results, spray coverage should be uniform and complete. If repeat treatments are needed, apply before crop emerges; the total of both treatments must not exceed 6 lb ae/A of glyphosate per crop. Glyphosate is tightly adsorbed or inactivated in the soil.
Site of action  Group 9: inhibits EPSP synthase
Chemical family  None generally accepted
CORN—Spot Treatment of Annual and Perennial Weeds
•  glyphosate
Rate  0.75 to 3.75 lb ae/A (1 to 5 lb ai/A)
Time  Apply to actively growing weeds before silking of corn.
Remarks  Rates depend on weed species and growth stage as specified on label.
Caution  Do not treat more than 10% of the area to be harvested. Sprayed crop will be killed. Avoid drift or spray outside target area for the same reason. Do not apply if weeds are stressed from drought, disease, or insect damage; weed control may be reduced. Rain within 8 hr after application may reduce effectiveness.
Site of action  Group 9: inhibits EPSP synthase
Chemical family  None generally accepted
CORN—Yellow Nutsedge Control
•  halosulfuron (Sandea)
Rate  0.5 to 1 oz ai/A (0.67 to 1.33 oz product/A)
Time  Apply to yellow nutsedge that is at three- to five-leaf stage.
Remarks  Add 1 to 2 quarts nonionic surfactant or crop oil concentrate per 100 gal spray solution for broadcast applications. A second application may be required 6 to 10 wk after the first.
Caution  Do not exceed 1.5 oz ai/A (2 oz/A product) or two applications per season. Note label for information on recropping or reseeding and site of application.
Site of action  Group 2: acetolactate synthase (ALS) inhibitor
Chemical family  Sulfonylurea
•  EPTC with safener (Eradicane) or
•  butylate with safener (Sutan +)
Rate  4 to 6.14 lb ai/A
Time  Apply preplant and incorporate immediately and thoroughly.
Remarks  Rate depends on soil type and infestation (consult label). Existing stands of perennial weeds must be turned under and chopped thoroughly before treatment. See label and Preplant Incorporated section of this chapter for additional application and incorporation instructions. Suppresses emerging shoots from yellow nutsedge tubers but does not necessarily kill them.
Site of action  Group 8: lipid synthesis inhibitor but not an ACCase inhibitor
Chemical family  Thiocarbamate
•  alachlor (Micro-Tech or Intrro) or
•  S-metolachlor (Dual Magnum or Dual II Magnum)
Rate  Refer to products in Preplant Incorporated section of this chapter
Remarks  Results are best when material is mechanically incorporated into the soil before planting. It appears that repeated applications inhibit new tuber formation and reduce infestations.
Caution  Alachlor is a restricted-use herbicide.
Site of action  Group 15: inhibits very long chain fatty acid synthesis
Chemical family  Chloroacetamide
•  bentazon (Basagran)
Rate  0.75 to 1 lb ai/A
Time  Apply when yellow nutsedge is 6 to 8 inches tall and, if needed, again at the same rate 7 to 10 days later.
Remarks  Results are best with two applications. Add oil concentrate to spray mix as label instructs. Refer to this product in Postemergence section of this chapter for additional remarks and cautions.
Site of action  Group 6: photosystem II inhibitor
Chemical family  Benzothiadiazole

Combining Herbicides
The purpose of combining herbicides is to exploit the strong properties of each herbicide while minimizing any weaknesses or undesirable properties. By combining herbicides at reduced rates, the grower can increase the spectrum of annual weeds controlled while reducing herbicide carryover. Residual carryover still persists to a certain degree. See label concerning the herbicides in use.
Under furrow irrigation, combinations are best applied preplant and incorporated. Some combinations (refer to labels), however, have been registered for application through sprinkler irrigation systems that incorporate them. This method of application is acceptable provided the herbicides are applied before weeds emerge.
Refer to each label for actual rates and further details concerning herbicide combinations. Component products may have slightly different labels; thus, rates and use directions may vary slightly.
Tank-mixes
Unless specifically prohibited on the label, herbicides registered for use on the same crop may be tank-mixed. Unless a tank-mix is recommended on a herbicide label, the grower, applicator, or person making the tank-mix recommendation will be responsible and liable for injury, nonperformance, or other problems associated with the application.

Package Mixes Labeled for Corn 
Trade Name	Ingredients	
Accent Gold WDG	6.5% nicosulfuron + 6.5% rimsulfuron + 19.1% flumetsulam + 51.7% clopyralid/lb	
Axiom	54.4% flufenacet + 13.6% metribuzin/lb	
Basis	50% rimsulfuron + 25% thifensulfuron/lb 	
Basis Gold	1.34% rimsulfuron + 1.34% nicosulfuron + 86.8% atrazine/lb	
Bicep Lite II Magnum	3.33 lb metolachlor + 2.67 lb atrazine/gal	
Bicep II Magnum	2.4 lb S -metolachlor + 3.1 lb atrazine/gal gal	
Brawl II ATZ	3.1 lb atrazine + 2.4 lb S -metolachlor/gal	
Brawn	3.1 lb atrazine + 2.4 lb S-metolachlor/gal	
Breakfree ATZ	2.25 lb atrazine + 3 lb acetochlor/gal		
Breakfree ATZ Lite 	1.5 lb atrazine + 4 lb acetochlor/gal	
Brozine	1 lb bromoxynil + 2 lb atrazine/gal	
Buctril + Atrazine	1 lb bromoxynil + 2 lb atrazine/gal	
Bullet	2.5 lb alachlor + 1.5 lb atrazine/gal	
Cadence ATZ	3 lb acetochlor + 2.25 lb atrazine/gal	
Cadence Lite ATZ 	4 lb acetochlor + 1.5 lb atrazine/gal	
Camix	3.34 lb S -metolachlor + 0.33 lb mesotrione/gal	
Celebrity	69.3% dicamba + 7.5% nicosulfuron/lb	
Celebrity Plus	42.4% dicamba + 17.0% diflufenzopyr + 10.6% nicosulfuron/lb gal	
Cinch ATZ	3.33 lb S-metolachlor + 2.67 lb atrazine/gal	
Cinch ATZ Lite	2.4 lb S -metolachlor + 3.1 lb atrazine/gal	
Clarion	37.5% nicosulfuron + 37.5% rimsulfuron/lb	
Confidence Xtra	4.3 lb acetochlor + 1.7 lb atrazine/gal	
Curtail	0.38 lb clopyralid + 2 lb 2,4-D amine/gal 	
Degree Xtra	2.7 lb acetochlor + 1.34 lb atrazine/gal	
Distinct	20% diflufenzopyr + 50% dicamba/lb	
Exceed	28.5% prosulfuron + 28.5% primisulfuron/lb	
Expert	1.74 lb S -metolachlor + 2.14 lb atrazine + 1 lb ai glyphosate/gal	
Field Master	2 lb acetochlor + 1.5 lb atrazine + 0.56 lb ae glyphosate/gal	
Fultime	2.4 lb acetochlor + 1.6 lb atrazine/gal	
Guardsman	2.33 lb dimethenamid-P + 2.67 lb atrazine/gal gal	
Guardsman Max	1.7 lb dimethenamid-P + 3.3 lb atrazine/gal	
G-Max Lite	2.25 lb dimethenamid-P + 2.75 lb atrazine/gal	
Harness Xtra	1.7 lb dimethenamid-P + 3.3 lb atrazine/gal	
Harness Xtra 5.6L	3.1 lb acetochlor + 2.5 lb atrazine/gal	
Hornet WDG	23.1% flumetsulam + 62.5% clopyralid/lb	
Imperium	5.6 lb EPTC + 1.4 lb acetochlor/gal	
Keystone	3 lb acetochlor + 2.25 lb atrazine/gal	
Keystone LA	4 lb acetochlor + 1.5 lb atrazine/gal	
Laddok	1.66 lb bentazon + 1.66 lb atrazine/gal	
Lariat	2.5 lb alachlor + 1.5 lb atrazine/gal	
Lexar	1.74 lb S -metolachlor + 0.224 lb mesotrione + 1.74 lb atrazine/gal	
Liberty ATZ	1 lb glufosinate + 3 lb atrazine/gal	
Lightning	0.42 lb imazethapyr + 0.14 lb imazapyr per 12.8-oz bottle 	
Lumax	2.68 lb S -metolachlor + 1 lb atrazine + 0.268 lb mesotrione/gal	
Marksman	1.1 lb dicamba + 2.1 lb atrazine/gal	
Medal II AT	3.1 lb atrazine + 2.4 lb S -metolachlor/gal	
NorthStar	7.5% primisulfuron + 39.9% dicamba/lb	
Parallel Plus	2.8 lb atrazine + 3.7 lb metolachlor/gal	
Priority	12.5% carfentrazone + 50% halosulfuron/lb 	
Recoil	1.58 lb glyphosate + 1.07 lb 2,4-D/gal	
Require Q (mp) 	48.2% dicamba + 6.25% rimsulfuron/lb	
Resolve Q (mp) 	18.4 % rimsulfuron + 4% thifensulfuron/lb	
Rifle Plus	1.1 lb dicamba + 2.1 lb atrazine/gal	
Sequence	2.25 lb glyphosate + 3 lb S-metolachlor/gal	
Shotgun F	2.25 lb atrazine + 1 lb 2,4-D ester/gal 	
Spirit	14.2% prosulfuron + 42.8% primisulfuron/lb	
Stalwart Xtra	3.1 lb atrazine + 2.4 lb metolachlor/gal	
Status	16% diflufenzopyr + 40% dicamba/lb	
Steadfast	50% nicosulfuron + 25% rimsulfuron/lb	
Steadfast ATZ	2.7% nicosulfuron + 1.3% rimsulfuron + 85.3% atrazine/lb 	
Sterling Plus	1.1 lb dicamba + 2.1 lb atrazine/gal	
Stout (mp) 	67.5% nicosulfuron + 5% thifensulfuron/lb	
SureStart	3.75 lb acetochlor + 0.38 lb clopyralid + 0.12 lb flumetsulam/gal	
Triangle	2.7 lb atrazine + 3.2 lb metolachlor/gal	
Volley ATZ	3 lb acetochlor + 2.25 lb atrazine/gal	
Volley ATZ Lite	4 lb acetochlor + 1.5 lb atrazine/gal	
WideMatch	0.75 lb fluroxypyr + 0.75 lb clopyralid	
Yukon	12.5% halosulfuron + 55% dicamba/lb	

Hops
Bob Parker
Revised October 20, 2008
HOPS—Annual Grass and Broadleaf Weeds
•  paraquat (Gramoxone Max, Firestorm or Gramoxone Inteon)
Rate  0.47 to 0.75 lb ai/A Gramoxone Max or Firestorm or 0.5 lb ai/A Gramoxone Inteon in at least 10 gal/A water. Add nonionic surfactant or crop oil concentrate to spray mix.
Time  For control of winter annuals, apply before hops begin to grow in spring. After hops begin to grow, apply after hop bines are at least 6 ft tall.
Remarks  Direct spray around base and in interspaces of hops. Retreatment or spot treatment may be necessary. Higher water volumes look more effective in desiccating hops in research trials.
Caution  A restricted-use herbicide. Do not let spray contact green portions of plant, or injury may result. Do not exceed three applications per season. Preharvest interval is 14 days. Do not graze animals in treated hopyard. Hop vine refuse and silage may be fed to livestock. Follow all safety precautions on label.
Site of action  Group 22: photosystem I electron diversion
Chemical family  Bipyridilium
•  norflurazon (Solicam)
Rate 2 to 4 lb ai/A norflurazon in 20 to 100 gal/A water
Time  Apply to soil surface in fall after hop yards have been worked for the last time, or within 1 wk after stringing in the spring.
Remarks  Use lower rate on coarse soils and higher rate on fine soils. Note recropping interval on label. Preharvest interval is 60 days.
Site of action  Group 12: bleaching; inhibits carotenoid biosynthesis
Chemical family  Pyridazinone
•  trifluralin (Treflan)
Rate 0.5 to 0.75 lb ai/A
Time  Apply and incorporate when crop is dormant.
Remarks  Use lower rate on coarse soils, higher rate on fine soils. Must be incorporated 1 to 2 inches with equipment that ensures soil mixing without injuring hop crowns. This treatment will not control mustards, prickly lettuce, horseweed (marestail), salsify, or nightshades.
Caution  Do not spray over hop crowns. Take care that incorporation equipment does not injure hop crown buds, needed to initiate hop bines. Disking operations that move additional treated soil onto the hop crown may delay emergence. Avoid exposing untreated soil when ditching for furrow irrigation.
Site of action Group 3: microtubule assembly inhibitor
Chemical family Dinitroaniline
•  glyphosate (Roundup Original II CA or Roundup WeatherMax)
Rate Consult labels
Time  Apply to actively growing weeds.
Remarks  Glyphosate will injure and kill hops, so keep it off hops. Remove any sucker that may be growing in area to be sprayed. Use a low-pressure, coarse spray to minimize drift within the hop yard. Glyphosate controls many perennial weeds if applied at the weed growth stage stated on the label.
Caution  Do not allow spray to contact green hop stems or foliage. Any crop receiving spray will be killed. Preharvest interval is 14 days.
Site of action  Group 9: inhibits EPSP synthase
Chemical family None generally accepted
HOPS—Certain Annual and Perennial Broadleaf Weeds
•  2,4-D (AgriSolutions 2,4-D Amine 4 or Weedar 64)
Rate 0.48 lb ae/A (1 pint/A product)
Time  Apply when annual broadleaf weeds are small.
Remarks  Controls susceptible broadleaf weeds. Make directed applications to the row middles. Make up to three applications with at least 30 days between treatments.
Caution  Avoid contact with new hop foliage and apical buds. Do not exceed 1.43 lb ae/A (3 pints product/A) per year crop cycle. Preharvest interval is 28 days. Avoid spray drift outside the target area.
Site of action  Group 4: synthetic auxin
Chemical family  Phenoxy acetic acid
•  clopyralid (Stinger)
Rate 0.125 to 0.25 lb ae/A (0.33 to 0.67 pint/A product)
Time  Apply after training when the growing points of the hop plants are above the spray zone.
Remarks  Special local needs labels ID-040011, OR-040038, and WA-040008. Clopyralid has a very narrow spectrum of activity and controls many weeds in the sunflower, legume (pea), and smartweed families. Hops may show some transient, minor leaf cupping where the spray contacts the lower leaves and suckers on treated plants. Test within a small area before treating the entire hop yard. The grower assumes all risk of crop injury, yield reduction, and crop loss. If a second application is required, the retreatment interval is 21 days.
Caution  Do not apply broadcast more than twice per crop per year. Do not exceed 0.25 lb ae/A per year. Preharvest interval is 30 days. Do not compost treated vegetation if compost will be used on sensitive plants.
Site of action  Group 4: synthetic auxin
Chemical family  Pyridine
HOPS—Certain Annual and Perennial Grass Weeds
•  clethodim (Select Max) 
Rate 0.068 to 0.12 lb ai/A (9 to 16 oz/A product)
Time  Apply to actively growing grasses at the size recommended on the label.
Remarks  Rate depends on target grasses. Add a nonionic surfactant at 0.25% v/v to the spray mix. Wait at least 14 days between applications. 
Caution  Preharvest interval is 21 days. Do not apply with ammonium sulfate. Do not exceed 16 fl oz/A (0.12 lb ai/A) in a single application or 64 fl oz/A (0.5 lb ai/A) per season.
Site of action  Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family  Cyclohexanedione
HOPS—Green Sucker Suppression in Hops
•  paraquat (Firestorm, Gramoxone Max, or Gramoxone Inteon)
Rate  0.5 lb ai/A Firestorm, or 0.5 to 0.75 lb ai/A Gramoxone Max, or 0.5 lb ai/A Gramoxone Inteon in at least 10 gal/A water. Add nonionic surfactant or crop oil concentrate to spray mix.
Time  Chemical pruning—To burn back existing vines and obtain even emergence of subsequent vines, spray when vines are less than 3 ft tall. Suckering and stripping—Spray only the basal 2 ft of vines. Repeat as necessary.
Remarks  Special local needs label ID-020009 for Gramoxone Max. Higher water volumes look more effective in desiccating hops in research trials. Hop response differs by variety. To determine sensitivity to injury, test selected use rate on a few of each variety of vine to be treated. Reduce rate or do not use on varieties showing unacceptable injury. Hop vine refuse and silage may be fed to livestock.
Caution  A restricted-use herbicide. Applications to hop vines less than 6 ft tall may cause unacceptable injury. Do not apply more than three times per season. Preharvest interval is 14 days. Do not allow animals to graze in treated hopyard. Follow all safety precautions on the label.
Site of action  Group 22: photosystem I electron diversion
Chemical family  Bipyridilium
•  carfentrazone (Aim EC)
Rate 0.03 lb ai/A (2 fl oz/A product) 
Time  Spray only the basal 18 inches of bines and the sucker mat at the base of the bine.
Remarks  Apply in at least 20 gal of spray solution with boom-type ground application equipment. Allow 14 days between treatments. Use a nonionic surfactant with at least 80% ai at 2 pints per 100 gal of spray solution or a quality crop oil concentrate at recommended rates. Controls only susceptible broadleaf weeds less than 4 inches tall or across.
Caution  Avoid applications until newly trained bines have developed sufficient barking to avoid damage to the stem and are high enough up the string to avoid contact with the apical bud. Do not exceed 0.119 lb ai/A (7.6 fl oz/A product) per season. Preharvest interval is 7 days. Avoid spray or drift outside the area.
Site of action  Group 14: protoporphyrinogen oxidase inhibitor
Chemical family  Triazinone