Indiana Corn, Soybeans: Postemergence Herbicide Considerations

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Photo: ©Debra L. Ferguson

Rain and storms have kept many Indiana farmers and custom applicators out of the field and likely delayed postemergence herbicide applications. As some fields begin to dry out enough to allow sprayers to reenter fields, farmers and custom applicators need to consider a couple of factors before spraying.

The delay has likely allowed weeds to grow well beyond their recommended postemergence application height of 4 to 6 inches.  Applicators may have to consider higher labeled rates to control those larger weeds. In same situations producers may need to consider an alternate or additional herbicides to control the larger weeds. 

Herbicide Resistance Info


During this delay not only have many of the weeds advanced past their optimal growth stage, but crops will also be approaching or exceeding growth stages in which herbicide applications may be restricted. As crops approach their reproductive stages the chances of herbicide injury and yield loss is increased.  

Two tables from the Ohio, Indiana, and Illinois Weed Control Guide are included in this article that outline the corn and soybean growth stage restrictions for many of the commonly used herbicides.

We also need to consider the replant intervals of postemergence herbicides to avoid herbicide residue carryover into the next crop as the month of July approaches. 

For example the fomesafen containing products that are often used on tough to control amaranths and ragweeds in have a 10-month replant interval for corn.  Applications made in July versus June will have a higher probably of causing carryover problems for next years corn crop.

The last thing we will mention is dicamba use in soybeans. As most of you are probably aware of by now, there have been widespread occurrences of offsite movement and damage to sensitive crops in the state of Arkansas.

They are considering very drastic measures which include a ban on dicamba applications for the rest of this growing season because of the amount of complaints filed with their state regulatory agency. 

As of this week (June 19), the situation here in Indiana has been relatively quiet, with just a few instances that I have observed in my trips to extension activities and research sites throughout the state. Most of these issues appear to be due to dicamba use in corn, and are consistent with what we have observed over the last 10-15 years.

We are however, about 3-5 weeks behind the southern US both in crop development, and postemergence weed control activities in soybean. So we anticipate that if we are going to run into the same issues as the southern US, that the next couple of weeks will tell us how successful we were in stewarding the dicamba resistant soybean technology.

So, we encourage all applicators to remember the label directions about Engenia, Xtendimax, and Fexapan, the only formulations labelled for use in Xtend beans when making spray applications.

While it has already been a difficult season for many farmers, they will need to keep these considerations in mind as they return to the fields to make postemergence applications in order to further protect their current crop yield as well reduce the risk of future crop injury.

Table 8. Rainfast Intervals, Spray Additives, and Crop Size for Postemergence Corn Herbicides This table shows the required time interval between herbicide application and rainfall and summarizes label recommendations for spray additives and maximum crop stage. Check herbicide labels for additive rates. Information in this table applies to field corn only.

Herbicide Rainfast Interval (hours) Spray additives/Maximum Crop Size (field corn)
2,4-D Amine 6-8 No additives. Broadcast up to 8-inch corn; directed spray before tassel stage.
2,4-D Ester 2-3 No additives. Broadcast up to 8-inch corn; directed spray before tassel stage.
Accent Q, NIC-IT 4 MSO, COC or SURF (Addition of UAN or AMS is recommended). Broadcast up to 6 collars or 20-inch corn; directed spray up to 10 collars or 36-inch field corn.
Aim 1 SURF. AMS or UAN may be added if required by tank-mix partner. Do not use COC or tank-mix with EC formulations of other crop protection chemicals except as specifically directed by label. Apply up to 8-collar corn.
Armezon PRO 1 MSO or COC plus UAN or AMS. Can use SURF in mixtures. Up to the V8 stage or 30-inch corn, whichever occurs first.
Atrazine 2 MSO or COC. Apply before corn is 12 inches tall.
Basagran 8 COC + UAN or AMS, depending on weed species present.
Beacon 4 COC or SURF (UAN or AMS may be added). Broadcast 4 to 20-inch corn; directed spray before tassel emergence.
Bestow 4 NIS + UAN or AMS. Broadcast up to 12 inches or 5-collar stage.
Bromoxynil 1 No additives. Apply before tassel emergence.
Bromoxynil+atrazine 2 No additives. Apply before corn is 12 inches tall.
Cadet 4 NIS, COC, or MSO. UAN or AMS can be added. Preplant up to 48 inches tall, and before tassel emergence.
Callisto 1 COC + UAN or AMS. Apply up to 30-inch or 8-leaf corn.
Callisto GT NIS + AMS. COC can be used instead of NIS but increases risk of crop injury. Broadcast up to 30-inch or V8 corn.
Callisto Xtra COC or NIS + UAN or AMS. Apply up to 12-inch corn.
Capreno 1 COC + UAN or AMS. Apply broadcast from V1 to V6 corn; directed spray up to V7 corn.
Dicamba 6-8 Add UAN if velvetleaf is present. SURF, COC, or UAN may be added under dry conditions. Do not apply with COC when corn height exceeds 5 inches. Broadcast up to 5th-leaf stage or 8-inch corn; directed spray up to 36-inch corn.
Dicamba/atrazine 6-8 Add UAN if velvetleaf is present. SURF, COC, or UAN may be added under dry conditions. Do not apply with COC when corn height exceeds 5 inches. Apply broadcast up to 5-leaf stage or 8-inch corn.
DiFlexx 6-8 Can add SURF, COC, or MSO + UAN or AMS. Broadcast spray from spike through V10 stage and corn less than 36 inches tall.
DiFlexx DUO 4 COC or MSO is recommended, plus UAN or AMS. HSOC can also be used. Broadcast up to but not including V7 stage, or 36 inches tall; directed spray up to V10 or 36 inches tall, or 15 days prior to tassel, whichever occurs first.
Glufosinate 4 AMS. Broadcast or directed up to 24-inch or V7 corn. Directed spray up to 36-inch corn.
Halex GT 2 SURF + AMS. Broadcast up to 30-inch or 8-leaf corn.
Harrow 4 SURF, COC, or MSO plus UAN or AMS. Broadcast from spike to 2-collar stage, and not more than 6 inches tall.
Hornet 2 SURF, COC, or MSO. UAN or AMS may be added under extremely dry conditions. Broadcast up to 20-inch corn or 6 collars; directed spray up to 36-inch corn.
Impact/Armezon 1 MSO or COC + UAN or AMS. SURF can be used in combinations with other broadleaf herbicides. Apply broadcast or directed up to 45 days before harvest.
Laddok 8 MSO, COC, UAN, AMS, DASH, or combinations of these. Apply before corn is 12 inches tall.
Laudis 1 MSO + UAN or AMS. Broadcast up to V8 corn.
Laudis + atrazine 2 COC + UAN or AMS. Broadcast up to 12-inch corn
Northstar 4 SURF, COC or MSO up to 12-inch corn. Only SURF between 12 and 36-inch corn. UAN or AMS may be added. Broadcast 4 to 20-inch corn; directed spray up to 36-inch corn.
Peak 4 COC unless mixed with glyphosate. Broadcast up to V6 or 20-inch corn; directed spray up to 30 inches.
Permit/Sandea/ Halomax 4 SURF, MSO, or COC. UAN or AMS may be added. Apply through layby stage of corn.
Realm Q 4 SURF or COC + UAN or AMS. Broadcast or directed up to 20 inches and prior to the 7-collar stage.
Revulin Q 4 COC or HSOC + UAN or AMS. Broadcast up to V5 stage or 20 inches tall, whichever occurs first.
Resolve Q 4 NIS + UAN or AMS, unless mixed with a glyphosate product or Ignite. Broadcast up to 20-inch or 6 collar corn.
Resource 1 COC. UAN or AMS may be added to improve control of certain species. Apply up to the 10-leaf stage.
Shotgun 6 No additives. Apply before 12-inch corn.
Solstice 1 COC or NIS + UAN or AMS. COC is preferred adjuvant. Do not use MSO. Up to V8 or 30-inch corn.
Spirit 4 COC, MSO or SURF.UAN or AMS may be added. Broadcast 4 to 20-inch corn; directed spray up to 24-inch corn or after 6 collar corn.
Starane 1 An adjuvant can be used if required by tank-mix partner. Broadcast up to the V5 stage; directed spray after the V5 stage.
Status 4 SURF, COC, or MSO + UAN or AMS. Broadcast from 4 to 36-inch corn (rates up to 5 oz/A)
Steadfast Q 4 COC, MSO, or SURF + UAN or AMS. COC or MSO is preferred over SURF. Broadcast up to and including 6 collars or 20-inch corn
Stinger 6-8 No additives. Up to 24-inch corn.
WideMatch 6 No additives. Broadcast up to the V5 stage; directed spray after the V5 stage.
Yukon 4 SURF or COC. UAN or AMS may be added. Apply broadcast or directed up to 36-inch corn.
Zemax 1 SURF or COC. Apply up to 30-inch or 8-leaf corn.

Table 18. Harvest and Feeding Intervals for Soybean Herbicides

Soybean Herbicides Days to Harvest – Grain Days to Harvest – Forage
Aim Apply up to third trifoliate Do not feed
Assure II/Targa 80 Do not feed
Basagran 30 30
Basagran + 2,4-DB 60 60
Basagran + thifensulfuron 60 Do not feed
Basagran + Reflex Apply prior to bloom Do not feed
Basagran + Cobra 90 Do not feed
Cadet 60 Do not feed
Cheetah Max 70 Do not feed
Classic Apply 60 days before maturity Do not feed
Clethodim 60 Do not feed
Cobra 45 Do not feed
Extreme/Tackle/
Thunder Master
Apply prior to bloom and 85 days before harvest Do not feed
FirstRate 70 25
Fomesafen 45 Do not feed
Fusilade DX Apply prior to bloom Do not feed
Fusion Apply prior to bloom Do not feed
Liberty/Cheetah Apply prior to bloom. Do not feed
Poast/Poast Plus 75 Do not feed1
Previx/Vise 90 Do not feed
Pursuit 85 Do not feed
Raptor 85 and apply prior to bloom Do not feed
Resource 60 Do not feed
Storm 50 Do not feed
Synchrony XP Apply 60 days before maturity Do not feed
Thifensulfuron 60 Do not feed
Torment 85 Do not feed
Ultra Blazer 50 Do not feed
Warrant Ultra 45 Do not feed

1Soybean hay may be fed.