Application of soil residual herbicides is important because they deliver a few weeks of residual weed control and aid in weed resistance management by incorporating additional site(s) of action in herbicide program. Several residual herbicides can be applied after corn emergence without injury to corn. A Few important factors should be considered when addressing weed control with residual herbicides applied after corn emergence:
- Corn growth stage,
- Weed height, and
- Tank-mix partner
Except some premix products such as Acuron, Harness Max, and Resicore with multiple herbicide active ingredients, these products generally do not have foliar activity and will not control weeds present at the time of application. Therefore, they should be tank-mixed with foliar active herbicides labeled in corn for control of existing weeds. Some of the herbicides, including Acuron, Anthem Maxx, Bicep II Magnum, Breakfree ATZ Lite, Degree Xtra, FulTime NXT, Keystone LA NXT, and Volley ATZ NXT contain active ingredients (such as atrazine) that has foliar activity. When applied at the correct weed growth stage, they will provide burndown activity (Table 1). Growers should consult product labels for additional information, such as the need for tank-mix partners or spray additives to improve control of existing weeds. For example, the post-emergence activity of atrazine can be increased by including an oil additive, yet additives should not be used if applying Balance Flexx or Corvus after corn emergence (Table 1).
Tank-mix partners may cause other effects regardless of the application timing. Follow application timing and other restrictions of tank-mix herbicide partner(s) as noted in the herbicide label. Table 1 has more specific information for residual herbicides that can be applied after corn emergence with regard to corn stage and weed height. Length and effectiveness of residual activity from in-crop herbicide application will vary depending on:
- Weed species present,
- Application rate of herbicide,
- Rainfall or irrigation following application (minimum of 0.5 inch within a week of application is ideal to activate residual herbicide),
- Density of the weed and crop canopy at the time of application, and
- Length of subsequent weed germination events.
|Herbicide||Corn Stage||Maximum Weed Stage|
|Aatrex / Atrazine||0-12”||1.5”|
|Armezon PRO||0-30” Or V8||4”|
|Bicep II Magnum / Cinch ATZ||0-12”||2-leaf|
|Bicep II Lite Magnum / Cinch ATZ Lite||0-12”||2-leaf|
|Bicep II Magnum||0-12”||2-leaf|
|Breakfree ATZ Lite||0-11”||unemerged|
|Dual II Magnum / Cinch||0-40”||unemerged|
|Harness Xtra / Confidence Xtra||0-11”||2-leaf|
|Keystone LA NXT||0-11”||unemerged|
|Lumax EZ / Lexar EZ||0-12”||3”|
|SureStart / TripleFLEX||0-11”||2” broadleaves|
|Zemax||30” or V8||5”|
a If Balance Flexx and Corvus is applied after the corn has emerged; do not add crop oil concentrate.
b Injury may occur if Callisto is applied post-emergence to corn that has been treated with Counter. Do not tank-mix Callisto with any organophosphate or carbamate insecticide. Do not cultivate within seven days of application.
Source: University of Nebraska CropWatch