Integrated Crop Management

Delayed soil-applied corn herbicide options

Recent rains across Iowa have halted field work and may have interfered with planned preemergence herbicide applications in corn. Corn and weed growth, however, continues. In situations where the corn, and most likely the weeds, have emerged prior to application of a planned soil-applied herbicide program, there are still options available. Most preemergence corn herbicides also can be applied postemergence in corn. A few exceptions include Axiom, Balance, and Epic, which may only be used prior to corn emergence. Many of the herbicides that can be used postemergence do not provide the same level and spectrum of weed control as they would when used prior to weed emergence. Individual fields should be monitored after application to verify the level of weed control obtained. Some herbicides may cause corn injury when applied postemergence under certain conditions so it is a good general rule to wait until the corn has recovered from environmental stresses before making postemergence herbicide applications.

The table below contains information outlining the recommended growth stage and height restrictions for corn and weeds when using some of the commonly soil-applied herbicides postemergence. A few additional comments pertaining to the use of these products postemergence are also included in the table. Remember to always refer to the individual herbicide labels for additional specific information such as rate adjustments, tank mix restrictions, insecticide interactions, adjuvant requirements, and other precautions regarding the use of these products in early postemergence applications.

Growth stage, plant height, and other considerations for postemergence applications of typically soil-applied herbicides

Herbicide Product Corn Height/Stage Maximum Weed Height/Stage Additional Comments
AAtrex, Atrazine 0-12" 1.5" grass, 4" broadleaves Include emulsifiable oil or crop oil for improved control.
Bicep II MAGNUM,

Cinch ATZ, Cinch ATZ Lite

Stalwart Xtra
Broadcast 0-5"; post-directed applications 5-12" corn Before 2-leaf stage Will provide control or partial control of less than 2-leaf grass and broadleaf weeds
Bullet, Lariat 0-5" Before 2-leaf stage Will provide control or partial control of less than 2-leaf grass and broadleaf weeds.
Callisto 0-30" or V8 5" Postemergence rate is 3 fl oz.
Camix 0-12" Prior to grass emergence, broadleaves less than 3" Will not provide consistent control of emerged grass weeds. NIS or COC may be added.
Define 0-5 leaf Prior to weed emergence Will not control emerged weeds.
Dual II MAGNUM, Cinch, Me-Too-Lachlor, Parallel 0-40" Prior to weed emergence Will not control emerged weeds.
Stalwart C Prior to weed emergence Refer to label for specific corn height restrictions.
Expert 0-12" 12" depending on rate Use postemergence only in glyphosate-resistant corn.
Fieldmaster 0-11" 12" depending on rate Use postemergence only in glyphosate-resistant corn.
Frontier, Outlook 0-12" Prior to weed emergence Will not control emerged weeds.
Guardsman Max, G-Max Lite 0-12" 1.5" Refer to label for additive recommendations.
Harness, Surpass, TopNotch, Degree 0-11" Prior to weed emergence Will not control emerged weeds.
Harness Xtra 0-11" Before 2-leaf grass stage
Hornet 0-20", V6 6" Include NIS, COC, or MSO with postemergence applications.
Degree Xtra, FulTime, Keystone, Keystone LA 0-11" Prior to weed emergence
Lasso, Micro-Tech 0-5" Prior to weed emergence Will not control emerged weeds.
Lexar 0-12" Less than 5" broadleaf weeds Will not provide consistent control of emerged grass weeds. NIS or COC may be added.
Lumax 0-12" Less than 3" broadleaf weeds Will not provide consistent control of emerged grass weeds. NIS or COC may be added.
Marksman 0-8", 5 leaf Not listed on label Refer to label for additive recommendations.
Prowl/Prowl H2O 0-30", V8 Prior to emergence Will not control emerged grasses.
Python Spike, 2" Prior to emergence Apply before first leaf is unfurled.

This article originally appeared on pages 86-87 of the IC-494(10) -- May 16, 2005 issue.


Source URL:
http://www.ipm.iastate.edu/ipm/icm//ipm/icm/2005/5-16-2005/delayed.html