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How to Manage Pests

UC Pest Management Guidelines


Yellow nutsedge, Cyperus esculentus.

Corn

Herbicide Treatment Table

(Reviewed 1/06, updated 7/09)

In this Guideline: More about weeds in corn:

Common name   R.E.I.+ P.H.I.+
(trade name) Amount/Acre (hours) (days)

  Calculate impact of pesticide on air quality
BEFORE PLANTING
A. ALACHLOR* 2.5–3 lb a.i. 12 NA
  (Micro-Tech) EC 2.5–3 qt    
  WSSA MODE OF ACTION GROUP NUMBER1: 15
  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. 12 NA
  (AAtrex 4L, Atrazine 4L) 3.2–4 pt    
  WSSA MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Do not rotate to any crop except corn or sorghum for 18 months after use. Band application can reduce carryover. Considered to be a ground water contaminant and requires a use permit within Ground Water Protection Areas.
 
C. EPTC 3.14–6.138 lb a.i. 12 NA
  (Eradicane) 6.7E 3.75–7.33 pt    
  WSSA MODE OF ACTION GROUP NUMBER1: 8
  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 1.375–4.5375 lb a.i.    
  (Roundup, etc.) 1–3.3 qt 4 NA
  WSSA MODE OF ACTION GROUP NUMBER1: 9
  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 1.42875–2.38 lb a.i.    
  (Dual Magnum) 1.5–2.5 pt 24 NA
  WSSA MODE OF ACTION GROUP NUMBER1: 15
  COMMENTS: Apply after preirrigation and incorporate into the soil.
 
F. PARAQUAT* 0.5–1 lb a.i.    
  (Gramoxone Inteon) 2–4 pts 24 NA
  WSSA MODE OF ACTION GROUP NUMBER1: 22
  COMMENTS: Apply as a contact broadcast spray to emerged weeds. Use a nonionic surfactant.
 
AT PLANTING
A. ALACHLOR* 2.5–3 lb a.i.    
  (Micro-Tech) EC 2.5–3 qt 12 see comments
  WSSA MODE OF ACTION GROUP NUMBER1: 15
  COMMENTS: Apply after preirrigation and incorporate in top 2 inches of soil within 7 days of planting. Do not apply after corn is 5 inches tall.
 
B. ATRAZINE* 1.6–2 lb a.i.    
  (Aatrex 4L, Atrazine 4L) 3.2–4 pt 12 see comments
  WSSA MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Do not follow with any crop except corn or sorghum for 18 months after use. Band application can reduce carryover. PHI for Aatrex is 0; for Atrazine it is 45 days for sweet corn and 60 days for field corn. Considered to be a ground water contaminant and requires a use permit within Ground Water Protection Areas.
 
C. S-METOLACHLOR 1.42875–2.38 lb a.i.    
  (Dual Magnum) 1.5–2.5 pt 24 0
  WSSA MODE OF ACTION GROUP NUMBER1: 15
  COMMENTS: Apply after preirrigation and incorporate into soil.
 
D. PENDIMETHALIN Label rates    
  (Prowl) 3.3EC 1–2 qt 24 0
  (Prowl H2O) 1–2 qt 24 0
  WSSA MODE OF ACTION GROUP NUMBER1: 3
  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 1.375–4.5375 lb a.i.    
  (Roundup) 1–3.3 qt 4 0
  WSSA MODE OF ACTION GROUP NUMBER1: 9
  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* 0.5–1 lb a.i.    
  (Gramoxone Inteon) 2–4 pts 24 0
  WSSA MODE OF ACTION GROUP NUMBER1: 22
  COMMENTS: Apply as a contact broadcast spray to emerged weeds. Use a nonionic surfactant.
 
G. EPTC 3.14–3.978 lb a.i.    
  (Eradicane) 6.7E 3.75–4.75 pt 12 0
  WSSA MODE OF ACTION GROUP NUMBER1: 8
  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 0.015–0.03093 lb a.i.    
  (Accent) WDG 0.33–0.66 oz 4 0
  WSSA MODE OF ACTION GROUP NUMBER1: 2
  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 24 0
  WSSA MODE OF ACTION GROUP NUMBER1: 3
  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
  (Roundup, Weathermax, Original, etc.) Label rates see label see label
  WSSA MODE OF ACTION GROUP NUMBER1: 9
  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 48 see comments
  WSSA MODE OF ACTION GROUP NUMBER1: 4
  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. PHI for field and popcorn is 0 days; for sweet corn it is 45 days.
 
E. DICAMBA*
  (Banvel) 0.25–0.5 lb a.i. (0.5–1 pt)    
  (Clarity) 0.5 lb a.i. (16 fl oz) 24 0
  WSSA MODE OF ACTION GROUP NUMBER1: 4
  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 12 32–corn forage
  WSSA MODE OF ACTION GROUP NUMBER1: 19
  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 24 0
  WSSA MODE OF ACTION GROUP NUMBER1: 6
  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* 0.25–0.5 lb a.i.    
  (Gramoxone Inteon) 1–2 pts 24 0
  WSSA MODE OF ACTION GROUP NUMBER1: 22
  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 12 60
  WSSA MODE OF ACTION GROUP NUMBER1: 5
  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 12 see comments
  WSSA MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Do not rotate to any crop except corn or sorghum or injury will occur. Band application can reduce carryover. PHI for Aatrex is 0; for Atrazine it is 45 days for sweet corn and 60 days for field corn. Considered to be a ground water contaminant and requires a use permit within Ground Water Protection Areas.
 
K. HALOSULFURON 0.0309–0.0623 lb a.i.    
  (Sandea) 0.66–1.33 oz 12 30
  WSSA MODE OF ACTION GROUP NUMBER1: 2
  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. Use a nonionic surfactant. Allow 30 days before harvesting for silage. Allow 9 months before planting back to alfalfa.
 
L. CARFENTRAZONE 0.000306 lb a.i.    
  (Shark) 0.33 oz 12 0
  WSSA MODE OF ACTION GROUP NUMBER1: 14
  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. HALOSULFURON/DICAMBA* 0.16875–0.3375 lb a.i.    
  (Yukon) 4–8 oz 12 see label
  WSSA MODE OF ACTION GROUP NUMBER1: 2/4
  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.
 
N. FORAMSULFURON 0.03281 lb a.i.   Grain: 70
  (Option) 1.5 oz 12 Forage: 45
  WSSA MODE OF ACTION GROUP NUMBER1: 2
  COMMENTS: Provides postemergent control or suppresses many annual grasses and certain broadleaves in field corn. Temporary yellowing or stunting may occur. Corn quickly outgrows these effects. The recommended additives are methylated seed oil (MSO) at 1.5 pt/acre plus 28% nitrogen at 2 qt/acre or ammonium sulfate at 3 lb/acre. Apply when annual grasses are 2 to 4 inches tall and before corn exceeds V5 or 16 inches, whichever comes first. Drop nozzles must be used to corn that is greater than V6 and less than V8 stage of growth. Do not apply to corn more mature than V8 (8 visible leaf collars) stage of growth. Can interact with organophosphate insecticides to cause severe corn injury; see label for specific restrictions pertaining to organophosphates.
 
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
* Permit required from county agricultural commissioner for purchase or use.
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 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.hracglobal.com.
NA Not applicable.

[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
D. J. Munier, UC Cooperative Extension, Glenn County
Acknowledgement for contributions to Weeds:
M. L. Campbell-Mathews, UC Cooperative Extension, Stanislaus County
R. N. Vargas, UC Cooperative Extension, Madera County

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