Corn Herbicide/Insecticide Precautions

A recent article published in this Bulletin by Dr. Mike Gray (“Soil Insecticide Use on Bt Corn Expected to Increase this Spring Across Much of Illinois”) provides insights and data that suggest the use of at-planting soil-insecticides in corn is likely to increase this season.  Many insecticide choices are available to farmers, but several of these could restrict the option to use certain corn herbicides.  Specifically, using an organophosphate (OP) insecticide at planting or after corn emergence could restrict the use of herbicides that inhibit either the ALS or HPPD enzymes.  The precautions and restrictions most often appear on the herbicide label and are due to the increased potential for corn injury following use of OP insecticides and ALS- or HPPD-inhibiting herbicides.

Why do certain combinations of OP insecticides and ALS- or HPPD-inhibiting herbicides increase the risk for corn injury?  Both insecticides and herbicides are foreign compounds to the corn plant.  The corn plant tries to “defend itself” against any potential injury a foreign compound might cause by attempting to render it inert or nonphytotoxic.  This process is commonly referred to as metabolism or breakdown of foreign compounds.  A corn plant has several different pathways to “detoxify” foreign compounds, but the OP insecticides and many ALS- and HPPD-inhibiting herbicides share a common metabolic pathway.  When an insecticide or herbicide is present within the plant, the plant is usually able to metabolize the compound before it may cause any deleterious effects.  However, if both insecticide and herbicide are present, the metabolism pathway cannot effectively metabolize both compounds.  When this happens, corn injury can result.

The following table is a summary of herbicide label statements about the potential interaction with organophosphate insecticides.  As always, be sure to consult the most current product labels for additional information.

 

Table 1.  Corn herbicide label statements: interactions with organophosphate (OP) insecticides.

Soil-applied OP insecticides

Foliar OP insecticide applied:
Corn herbicide Counter
Thimet Lorsban Aztec Fortress Days before Days after
nicosulfuron and rimsulfuron
Accent Q No UCI UCI Yes Yes 7 3
Basis Noa Noa Noa Yes Yes 7 3
Basis Blend Nob UCI UCI Yes Yes 7 3
Instigate Nob UCI UCI Yes Yes 7 3
Prequel No No No Yes Yes
Require Q No Noa Noa Yes Yes 7 3
Realm Q Nob UCI UCI Yes Yes 7 3
Resolve Q Noc Noc Noc Yes Yes
Steadfast Q No UCI UCI Yes Yes 7 3
Stout No UCI UCI Yes Yes 7 3
primisulfuron and prosulfuron
Beacon No TCI TCI TCI TCI 10 7
Northstar No TCI TCI TCI TCI 10 7
Spirit No TCI TCI TCI TCI 10 7
flumetsulam
Hornet WDG (PRE) No No TCId TCId TCId
Hornet WDG (POST) No No TCId TCId TCId 10 10
Python No No TCId TCId TCId
SureStart/TripleFlex (PRE) No No TCId TCId TCId
SureStart/TripleFlex (POST) No No TCId TCId TCId 10 10
thifensulfuron
Harmony SG No UCI UCI Yes Yes
mesotrione
Callisto SCI SCI 7 7
Callisto Xtra SCI SCI 7 7
Halex GT SCI SCI SCI SCI SCI 7 7
Lexar EZ SCI TCI TCI TCI TCI 7 7
Lumax EZ SCI TCI TCI TCI TCI 7 7
Zemax SCI SCI SCI SCI SCI 7 7
thiencarbazone
Corvus No Yes Yes Yes Yes 7 7
Capreno No No No Yes 7 7
saflufenacil
Sharpen No No No Yes Yes
Verdict No No No Yes Yes

No = Do not use this herbicide on corn if this insecticide was previously applied

Yes = The herbicide may be applied to corn previously treated with this insecticide

Abbreviations:

UCI = unacceptable crop injury

TCI = temporary crop injury

SCI = severe crop injury

–          = no information on label

aDo not apply within 60 days of crop emergence where an OP insecticide was applied.

bDo not apply within 45 days of crop emergence where Counter was applied.

cDo not apply within 45 days of crop emergence where an OP insecticide was applied.

dSoil-applied OP insecticides should not placed in furrow, but rather applied in a band or T-band.