Corn is or will be emerging soon now. If there are any problems with corn emergence, herbicides may be blamed as the cause. However, herbicides may or may not be the culprit. A few points should be remembered if you encounter any emergence problems.
Corn Herbicide Injury
Chris Boerboom, Ext. Weed Scientist
Corn is or will be emerging soon now. If there are any problems with corn emergence, herbicides may be blamed as the cause. However, herbicides may or may not be the culprit. A few points should be remembered if you encounter any emergence problems.
First, corn must germinate before a herbicide can cause damage. This means that a whole, unsprouted, dead kernel was not killed by a herbicide. However, if the kernel has a radicle or sprout, then there is potential for herbicide uptake and damage.
Next, we need to consider the modes of action of the herbicides and the potential for injury. For instance, there are three herbicide modes of action that require light for activity such as the photosynthetic inhibitors (i.e. atrazine, Princep, Sencor), pigment inhibitors (i.e. Balance, Callisto, which is in Lumax and Camix, Command carryover), and PPO inhibitors (such as with Flexstar carryover). These herbicides will not damage the tissue of a seedling while it is underground and protected from sunlight. As seedlings emerge and are exposed to light, these herbicides can then cause damage.
Other herbicide modes of action can damage corn seedlings as they are sprouting. These modes of action include the ALS inhibitors (i.e. Python or the flumetsulam in Hornet, carryover of Pursuit, Classic), growth regulators (i.e. 2,4-D, dicamba), seedling root growth inhibitors (i.e. Prowl), and seedling shoot growth inhibitors (i.e. Define, Dual, Harness, Outlook). While these herbicide modes of action have the potential to damage or stunt seedlings, it would be highly unusual for them to kill corn.
Glyphosate or Gramoxone applied as burndown treatments do not have residual soil activity to affect germinating corn. However, even if corn is just starting to spike, glyphosate can seriously damage non-Roundup Ready corn.
Of course, other reasons for injury such as seedling disease, insect damage, soil crusting, fertilizer burn, frost, etc. still need to be considered as potential reasons for poor corn emergence or growth. Herbicides are not the only reason for poor corn emergence or growth.
Examples of corn seedling injury symptoms from these herbicide modes of action.
Pigment inhibitors: bleached or white leaves
PPO inhibitors: seedlings may have burning or striping in the veins (image is an example of Flexstar carryover)
ALS inhibitors: classic symptoms include stunted shoot growth and bottle brush roots (fine, short lateral roots)
Growth regulators: symptoms may range from pruned roots, to shoot abnormalities, which may mimic seedling shoot growth inhibitors, to onion leafing
Seedling root growth inhibitors: classic symptoms are pruned roots with clubbed root tips
Seedling shoot growth inhibitors: classic symptom is leafing out underground
Glyphosate: symptoms of applications to spike corn may range from whitening, to stunting, to death
