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How to Manage Pests

UC Pest Management Guidelines

| More pests | More crops | About guidelines |

Yellow nutsedge, Cyperus esculentus.

Corn

Herbicide Treatment Table

(Reviewed 1/06, updated 1/06)

In this Guideline: More about weeds in corn:
Common name Amount/Acre P.HI+
(trade name)   (days)
BEFORE PLANTING
A.    ALACHLOR* 2.5–3 lb a.i.  
  (Lasso) EC 2.5–3 qt  
  MODE OF ACTION: A chloroacetamide (Group 15)1 herbicide.
  COMMENTS: Apply after preirrigation and incorporate in top 2 inches of soil within 7 days of planting.
       
B. ATRAZINE* 1.6–2 lb a.i.  
  (AAtrex 4L, Atrazine 4L) 3.2–4 pt  
  MODE OF ACTION: A chloroacetamide (Group 15)1 herbicide.
  COMMENTS: Do not rotate to any crop except corn or sorghum for 18 months after use. Band application can reduce carryover.
   
C. EPTC 3.14–6.138 lb a.i.  
  (Eradicane) 6.7E 3.75–7.33 pt  
  MODE OF ACTION: A thiocarbamate (Group 8)1 herbicide.
  COMMENTS: Immediate incorporation is necessary. Use high rates for perennial weeds. Requires cross-discing for best results. Some corn varieties are sensitive to injury with this material; check with corn seed companies to insure a variety is tolerant before using. Do not apply greater than 4.75 pt/acre in the 10 southernmost counties of California. Soils lacking enough moisture for seed germination must be pre-irrigated before application.
   
D. GLYPHOSATE 1–4 lb a.i.  
  (Roundup) 1–4 qt  
  MODE OF ACTION: A glycine (Group 9)1 herbicide.
  COMMENTS: A nonselective herbicide; apply to emerged weeds. Do not allow spray mist to contact desirable plants. Use with a nonionic surfactant.
   
E. S-METOLACHLOR 1.43–2.38 lb a.i.  
  (Dual Magnum) 1.5–2.5 pt  
  MODE OF ACTION: A chloroacetamide (Group 15)1 herbicide.
  COMMENTS: Apply after preirrigation and incorporate into the soil.
   
F. PARAQUAT* 0.56–1 lb a.i.  
  (Gramoxone Max) 1.5–2.7 pts  
   
  MODE OF ACTION: A bipyridylium (Group 22)1 herbicide.
  COMMENTS: Apply as a contact broadcast spray to emerged weeds. Use a nonionic surfactant.
   

AT PLANTING
A. ALACHLOR* 2.5–3 lb a.i.    
  (Lasso) EC 2.5–3 qt    
  MODE OF ACTION: A chloroacetamide (Group 15)1 herbicide.  
  COMMENTS: Apply after preirrigation and incorporate in top 2 inches of soil within 7 days of planting.  
     
B. ATRAZINE* 1.6–2 lb a.i.    
  (Aatrex 4L, Atrazine 4L) 3.2–4 pt    
  MODE OF ACTION: A triazine (Group 5)1 herbicide.  
  COMMENTS: Do not follow with any crop except corn or sorghum for 18 months after use. Band application can reduce carryover.  
     
C. S-METOLACHLOR 1.43–2.38 lb a.i.    
  (Dual Magnum) 1.5–2.5 pt    
  MODE OF ACTION: A chloroacetamide (Group 15)1 herbicide.  
  COMMENTS: Apply after preirrigation and incorporate into soil.  
     
D. PENDIMETHALIN 0.825–1.65 lb a.i.    
  (Prowl) 3.3EC 1–2 qt    
  MODE OF ACTION: A dinitroaniline (Group 3)1 herbicide.  
  COMMENTS: Irrigate to activate; do not incorporate. Do not apply to no-till corn. Plant at least 1.5 inches deep. Do not use on peat soils.  
   
E. GLYPHOSATE 1–4 lb a.i.    
  (Roundup) 1–4 qt    
  MODE OF ACTION: A glycine (Group 9)1 herbicide.    
  COMMENTS: Apply to emerged weeds but before corn emerges. Do not allow spray mist to contact desirable plants. Use with a nonionic surfactant.  
     
F. PARAQUAT* 0.56–1 lb a.i.  
  (Gramoxone Max) 1.5–2.7 pts  
  MODE OF ACTION: A bipyridylium (Group 22)1 herbicide.
  COMMENTS: Apply as a contact broadcast spray to emerged weeds. Use a nonionic surfactant.
       
G. EPTC 3.14–4 lb a.i.  
  (Eradicane) 6.7E 3.75–4.75 pt  
  MODE OF ACTION: A thiocarbamate (Group 8)1 herbicide.
  COMMENTS: Immediate incorporation is necessary. Use high rates for perennial weeds. Requires cross-discing for best results. Some corn varieties are sensitive to injury with this material; check with corn seed companies to insure a variety is tolerant before using. Do not apply greater than 4.75 pt/acre in the 10 southernmost counties of California. Soils lacking enough moisture for seed germination must be pre-irrigated before application.
   

AFTER PLANTING

 
A. NICOSULFURON 0.015–0.031 lb a.i.  
  (Accent) WDG 0.33–0.66 oz  
  MODE OF ACTION: A sulfonylurea (Group 2)1 herbicide.
  COMMENTS: Do not apply to sweet corn. Apply postemergent until corn is 20 inches tall or 6 leaf stage of corn, whichever comes first, then use drop nozzles up to 36 inches. Keep spray out of whorl. Injury will occur if applied to stressed corn and it won't effectively control stressed weeds. See label for cultivation restrictions. Deep plowing will reduce risk of carryover. Must use with surfactant or COC (crop oil concentrate). Use a minimum of 15 gpa for best performance. Use higher rates as weed size increases.  
   
  Nicosulfuron can be tank mixed with dicamba or bromoxynil to broaden the weed control spectrum. This material is best used in conjunction with other methods of control to reduce the risk of the development of resistance by weeds.
     
B. PENDIMETHALIN 0.825–1.65 lb a.i.  
  (Prowl) 3.3 EC 1–2 qt  
  MODE OF ACTION: A dinitroaniline (Group 3)1 herbicide.
  COMMENTS: Apply as culti-spray after brace roots are formed. May contribute to lodging. Pendimethalin can be active up to 6 months; check the label for plant-back restrictions. Will not control emerged weeds.
   
C. GLYPHOSATE 1–4 lb a.i.  
  (Roundup, Weathermax, Original, Ultramax) 1–4 qt  
  MODE OF ACTION: A glycine (Group 9)1 herbicide.
  COMMENTS: Can be applied as a spot treatment, but apply before corn silks in conventional corn varieties. Corn in treated area will be killed unless it is a Roundup-tolerant variety. Do not allow spray mist to contact desirable plants. Use with a nonionic surfactant. In Roundup Ready varieties glyphosate can be applied over the top to corn up to the V8 stage of corn or 24 inches. Drop nozzles are recommended for corn taller than 24 inches. Keep spray out of whorls after corn is 30 inches tall. Rates depend on formulation and weed type and size. Must sign technology agreement. Application of 1-2 percent dry ammonium sulfate by weight per 100 gal. of water may increase performance. Use extreme care to prevent drift onto nonRoundup Ready crops.
       
D. 2,4-D* 0.2375–0.475 lb a.i.  
  (Amine) 0.5–1 pt  
  MODE OF ACTION: A phenoxy-carboxylic-acid (Group 4)1 herbicide.
  COMMENTS: Apply from crop emergence to tasseling. Apply over the top when corn is less than 8 inches tall. Use drop nozzles when corn is more than 8 inches tall, keeping spray mist out of whorl. Don't use when corn is over 3 feet tall or when brace roots have formed. Do not spray when temperature is expected to exceed 95°F. High drift potential; keep away from sensitive crops. Tanks must be thoroughly cleaned because even minute amounts of residue will cause injury to broadleaf crops. In many areas there are restrictions limiting use of this material. Delay cultivation 8-10 days to prevent stalk breakage due to temporary brittleness caused by 2,4-D.
       
E. DICAMBA*    
  (Banvel) 0.25–0.5 lb a.i. (0.5–1 pt)  
  (Clarity) 0.5 – 0.75 lb a.i. (16–24 fl oz)  
  MODE OF ACTION: A benzoic acid (Group 4)1 herbicide.
  COMMENTS: Do not use on sweet corn. Apply over the top when corn is less than 8 inches tall. Use drop nozzles when corn is more than 5 leaves or 8 inches tall. Apply postemergence until corn is 36 inches tall or until 15 days before tassels emerge. Keep herbicide out of the whorl of the plant to avoid yield loss. Do not apply when temperature is expected to exceed 85°F. High drift potential; keep away from sensitive crops. Keep spray pressure below 20 psi. Tanks must be thoroughly cleaned because even minute amounts of residue will cause injury to broadleaf crops. In many areas there are restrictions limiting the use of this material. Clarity has less potential to move off target than Banvel. Do not cultivate within 7 days after application. Applications during rapid growth may result in temporary leaning.
       
F. DIFLUFENZOPYR 0.175–0.2625 lb a.i. 72–grain
  (Distinct) 4–6 oz 32–corn forage
  MODE OF ACTION: A phthalamate semicarbazone (Group 19)1 herbicide.
  COMENTS: For use in field corn and popcorn. Used to control annual broadleaves and control/suppress many perennial broadleaves. Tank-mix or use sequentially with a grass herbicide.
       
G. BROMOXYNIL 0.125–0.25 lb a.i.  
  (Buctril) 0.5–1 pt  
  MODE OF ACTION: A nitrile (Group 6)1 herbicide.
  COMMENTS: For field corn and popcorn only. Apply after crop emergence but before tassels emerge. Weed should be less than 4 inches tall. Can be used where drift of dicamba or 2,4-D may injure sensitive broadleaf crops. Do not apply to sweet corn. Combinations of bromoxynil with other broadleaf herbicides enhance weed control.
       
H. PARAQUAT* 0.56–1 lb a.i.  
  (Gramoxone Max) 1.5–2.7 pts  
  MODE OF ACTION: A bipyridylium (Group 22)1 herbicide.
  COMMENTS: Apply to emerged weeds. Use shielded spray when corn is at least 10 inches. Do not allow spray mist to contact corn plants. Use a nonionic surfactant.
       
I. METRIBIZIN 0.075–0.14 lb a.i.  
  (Sencor) 75 DF 1.6–3 oz  
  MODE OF ACTION: A triazinone (Group 5)1 herbicide.
  COMMENTS: Do not use on corn grown for seed, sweet corn, popcorn, or white corn. Use postemergence as a tank mix with nicosulfuron (Accent), atrazine (AAtrex, etc.), dicamba (Banvel), bromoxynil (Buctril), or 2,4-D to increase number of species controlled, improve control of larger weeds, and/or reduce herbicide rates (see label). The mixture with nicosulfuron is allowed by a 2ee label (CASNPB96.074), which is not on the container label. The maximum size of corn or weeds and the use of broadcast or directed sprays varies with the tank mixture being applied. Do not apply when the corn is under stress, including very dry or very wet soil conditions. Do not use on sand, loamy sand, or sandy loam soils that have less than 0.5% organic matter. Do not use crop oil concentrate (COC) or any adjuvant containing vegetable or petroleum oils with any metribuzin tank mixture as severe leaf burn, crop stunting, and/or stand reduction may occur.
       
J. ATRAZINE* 1.6–2 lb a.i.  
  (Aatrex 4L, Atrazine 4L) 3.2–4 pt  
  MODE OF ACTION: A triazine (Group 5)1 herbicide.
  COMMENTS: Do not rotate to any crop except corn or sorghum or injury will occur. Band application can reduce carryover. Considered to be a ground water contaminant and requires a use permit within Ground Water Protection Areas.
   
K. HALOSULFURON 0.031–0.063 lb a.i.  
  (Sempra) 0.66–1.33 oz  
  MODE OF ACTION: A sulfonylurea (Group 2)1 herbicide.
  COMMENTS: For use on field corn or field corn grown for seed. Can be applied to sweet corn or popcorn however at lower use rates. Apply over corn beginning at the spike stage until row closure, or until the height of the corn prevents coverage of weed with spray. To avoid the development of resistance to this herbicide by weeds, do not use this material in consecutive years. See label for spray rates and application timing, which are based on weed size. Can be tank mixed with dicamba (Banvel), 2,4-D, or bromoxynil (Buctril) to increase the spectrum of weeds controlled or if weed size is too large for just halosulfuron alone. Can also be tank mixed with glyphosate in Roundup Ready varieties. Always use with an adjuvant of either a nonionic surfactant or oil concentrate. Allow 30 days before harvesting for silage. Allow 9 months before planting back to alfalfa.
   
L. CARFENTRAZONE 0.008 lb a.i.  
  (Shark) 0.33 oz  
  MODE OF ACTION: A triazolinone (Group 14)1 herbicide.
  COMMENTS: Apply in all tillage systems up to 30 days before planting and afterwards up to 8-leaf stage of corn. Do not apply more than 1.24 oz/season. For best performance apply to weeds before weeds exceed 4 inches. However, can be applied to velvetleaf up to 18 inches tall, or 36 inches tall with drop nozzles. Do not apply to stressed crops or use with an oil concentrate or severe speckled leaf burn may occur. Tank mixing with 2,4-D, Clarity, or Accent will widen the weed control spectrum. Can also be tank mixed with glyphosate in Roundup Ready systems.
   
M. HALSULFURON/DICAMBA 0.16875–0.3375 lb a.i.  
  (Yukon) 4–8 oz  
  MODE OF ACTION: A sulfonylurea (Group 2)1 and a benzoic acid (Group 4)1 herbicide.
  COMMENTS: For use on field corn and field corn grown for seed. Can be applied over-the-top or with drop nozzles from the spike through 36 inches. May be applied up to 2 applications not to exceed 8 ounces. Allow at least 2 weeks between applications. Allow 9 months before planting back to alfalfa.
   
 
*   Permit required from county agricultural commissioner for purchase or use.
+ Preharvest interval. Do not apply within this many days of harvest.
1 Group numbers are assigned by the Weed Science Society of America (WSSA) according to different modes of action. Although weeds may exhibit multiple resistance across many of the groups, mode of action numbers are useful in planning mixtures or rotations of herbicides with different modes of action. For more information see http: //www.plantprotection.org/HRAC/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Corn
UC ANR Publication 3443
Weeds
S. D. Wright, UC Cooperative Extension, Tulare County
W. M. Canevari, UC Cooperative Extension, San Joaquin County
M. L. Campbell-Mathews, UC Cooperative Extension, Stanislaus County
R. N. Vargas, UC Cooperative Extension, Madera County

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