Early Season Corn Herbicide Injury
Review
Chris Boerboom
UW Extension Weed Scientist
The mechanism that allows corn plants to tolerate most soil applied
herbicides is metabolism, which is when the corn seedling detoxifies the
herbicide soon after entering the plant. When a corn seedling is growing
under stress conditions, the rate of herbicide metabolism can be reduced
and result in injury. This spring's cold temperatures could be a stress
that is slowing herbicide metabolism compared to a normal spring. The potential
for herbicide injury is also affected by the amount of herbicide absorbed
by the corn seedling. Ample rain and higher soil moisture levels can move
herbicides into the seed zone and increase herbicide availability and uptake
into seedlings. This spring's drier conditions may actually be decreasing
the amount of herbicide uptake by corn seedlings. Regardless, this cold
spring is certainly creating stress conditions for our corn crop, and herbicide
damage will likely be blamed for some of the problems with emergence and
early season growth. As a brief review of some of the common early season
corn injury symptoms, I have listed several symptoms that are associated
with stunted corn seedlings, potential herbicide culprits, and several
non-herbicide mimics. To help diagnose herbicide injury complaints in corn,
I would also suggest a review of the bulletin "Herbicide Mode of Action
and Injury Symptoms," publication number NCR377.
Leafing out underground, or buggy whipping,
plants with normal roots.
- Seedling shoot inhibitors such as Dual II, Frontier, Lasso, Harness,
and Surpass. Dual II, Harness, and Surpass contain safeners designed to
enhance the metabolism of these herbicides and reduce the risk of injury.
The severity of injury may be increased when these herbicides are tank
mixed with preemergence applications of dicamba.
- Soil crusting is a classic mimic.
Stunting plus pruned roots, purplish shoots
possible.
- ALS-inhibiting herbicides such as Broadstrike or Hornet. The severity
of injury can be increased with certain applications of organophosphate
insecticides. Carryover from late season Pursuit applications from last
year's soybeans could also be considered.
- Soil compaction is a mimic.
Stunting plus pruned roots with clubbed root
tips, purplish shoots possible.
- Seedling root inhibitors (cell division inhibitors) such as Prowl or
carryover from Treflan or Sonalan. Corn roots growing in Prowl treated
soil will be stunted. Therefore, Prowl should never be incorporated and
corn should be planted at least 1.5 inches deep so the roots develop below
the Prowl treated soil.
- Needle nematode is a mimic and causes pockets of damage in fields with
sandy soil. Several cases have been reported in Wisconsin. See pages 71-73
in the Field Crops Pest Management in Wisconsin bulletin for more information.
Stunting plus pruned roots with brown root
tips.
- Causes may range from fertilizer burn to root pathogens. No herbicide
specifically burns root tips, but damage from root pathogens may be a secondary
effect.
Stunting plus onion leafing, root proliferation
possible.
- Growth regulators such as dicamba (Banvel, Clarity, Marksman) and 2,4-D.
Risk of injury increases with preemergence applications.
Bleached corn leaves, roots normal.
- Command carryover or Command drift. Spray drift from both Command formulations
can bleach corn.
Roundup Ultra spray drift or Roundup Ultra burndown treatment
to corn that is just spiking. Very low rates of Roundup Ultra can bleach
corn and mimic Command bleaching.
For more information contact Mike
Rankin