Herbicide Corn Maturity Cutoffs

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Due to little time and very few good spray days, some corn fields have yet to have their layby application. Corn is putting on a new leaf every 3 days with all the heat and water. Therefore, time is short before it will be too mature to apply many herbicides safely over the top.

How large can corn be before glyphosate could potentially cause injury? The glyphosate label states it can be applied up through the V8 corn growth stage. My experience has been if glyphosate is applied to corn larger than that it can at times cause ears to be barren.  This phenomenon is difficult to predict ahead of time as it can vary due to maturity of the corn at application, hybrid and weather.

Crop stage and/or crop height is used to determine the cutoffs for a given herbicide.  Often the label states the limits at whichever (crop stage or crop height) comes first.  Crop stage can easily be done by counting the number of leaf collars that are fully exposed (Ex: 4 collars = 4 leaf) (Picture below).  If tankmixing, cutoff is always determined by the most limiting factor.

4 – Leaf Corn

Johnsongrass Escaping Glyphosate Burndown

Postemergence Corn Herbicides Crop Height Cutoff Crop Stage Cutoff
Accent 20 inches 6 leaf
Acuron GT 30 inches 8 leaf
Atrazine (Bicep, Degree Xtra, Acuron, etc.) 12 inches
Callisto* 30 inches (without atrazine)
Capreno* 20 inches 7 leaf (without atrazine)
Corvus 2 leaf
Dicamba (Clarity, etc.) 8 inches (1 pt/A) or
36 inches (1/2 pt/A)
5 leaf

Distinct 24 inches
Glyphosate – RR corn only 30 inches 8 leaf
Halex GT 30 inches 8 leaf
Armezon/Impact 8 leaf
Laudis 8 leaf
Liberty – LL corn only 24 inches 7 leaf
Diflexx 36 inches 10 leaf
Realm Q 20 inches 7 leaf
Resicore 11 inches
Resolve Q 20 inches 7 leaf
Roundup PM – RR corn only 8 leaf
Shield Ex 20 inches 6 leaf
Status 36 inches 10 leaf
Steadfast Q 20 inches 7 leaf
Storen 8 leaf
2,4-D 8 inches

*Note that if atrazine is added to herbicides such as Callisto or Capreno for example, the cutoff would be reduced to 12 inches.


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