Corn: Herbicide Injury
| Author: |
OMAFRA Staff
|
| Creation Date: |
01 March
2002
|
| Last Reviewed: |
01 March
2002
|
Excerpt from Agronomy Guide for Field Crops (Chapter
3)
Table of Contents
- Introduction
- Specific Types of Herbicide Injury
- Updates on Corn: Herbicide Injury
- Related links...
Introduction
All herbicides have the potential to cause crop injury. Some soil
applied (preplant or preemergent) herbicides can be splashed up on
the leaves to cause injury, or the roots can take up the herbicide.
With post-emergent herbicide products, most injury results at or shortly
after application. Spray from the target crop onto a neighbouring
non-target crop can also cause injury when the non-target crop is
susceptible to the herbicide being applied. Spray overlaps are also
common places where crop injury from herbicides can occur.
Stage of growth, crop stress, weather conditions, variety, tank
mix partners and adjuvants can all affect the amount and severity
of crop injury. When the target crop is under stress, it is sometimes
not able to metabolize the herbicide fast enough to avoid injury.
The type of herbicide (mode of action) is a major factor in how herbicides
affect crops. In general, while contact herbicide injury may look
worse, systemic herbicides will have longer-lasting and more detrimental
injury, which may be more severe to the crop. Always read the label
for information on how to reduce the risk for herbicide injury.
For more information, see the OMAFRA Factsheet, Herbicide
Mode of Action Categories, or to
order Order No. 00-061, or visit the OMAFRA Web site at www.omafra.gov.on.ca/english/crops/.
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Specific Types of Herbicide Injury
| Dinitroaniline | Chloroacetamide
| Bleaching Herbicides | Auxinic
Herbicides | Bromoxynil |
| Acetolactase Synthase (ALS) | ACCase
Inhibitors | Glufosinate Ammonium | Glyphosate
|
Refer to the OMAFRA Factsheet, Herbicide
Mode of Action Categories, or to
order the factsheet Order No. 00-061, or Publication
75, Guide to Weed Control, for herbicide trade names.
Dinitroaniline injury on corn caused by high rates or slow breakdown
is shown . Short roots with thickened root tips or stunted top growth
with purplish leaves are common symptoms.

Plate 40. Dinitroaniline injury on corn.
Plate 41 displays chloroacetamide injury on corn. Leaves are shortened,
puckered and the coleoptile is twisted, with the leaves unable to
unfurl properly. Plant stress can reduce the plant metabolism and
ability to breakdown herbicide and causes more injury.

Plate 41. Chloroacetamide injury on corn.
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Bleaching Herbicides (e.g.,
isoxaflutole, clomazone)
Plate 42 shows bleached leaves on corn caused by isoxaflutole
at high rates. Plants may emerge normally and then show symptoms at
the 2-4-leaf stage. Symptoms may also occur after a rain. Leaves will
appear yellow to white and are usually more pronounced near the midrib.
Purpling may appear at the leaf margin or at the base of the whorl.

Figure 42. Isoxaflutole injury. Bleached leaves
on corn caused by isoxaflutole at 4X rate, normal field rate and check
(no herbicide).
Auxinic Herbicides and Other Products
Containing These Herbicides (e.g., 2,4-D,
MCPA, dicamba,
clopyralid)
Plate 43 shows the "onion leaf" symptom on
corn caused by high rates of dicamba (this can also occur on sensitive
hybrids or when applied too late).

Plate 43. "Onion leaf" symptom on corn
caused by auxinic herbicides.
Dicamba injury causes twisted brace roots on corn.
Brace roots are gnarled and tend to grow together and do not grow
into the soil to support the plant, leading to potential lodging late
in the season. High rates, sensitive hybrids or late applications
can all cause these symptoms.

Plate 44. Dicamba injury causes twisted brace roots
on corn.
Plate 45 shows the effect on pollination when sprayed
too late.

Plate 45. Auxinic herbicide injury on ears of corn
(example 2,4-D, dicamba).
Plate 46 shows bromoxynil injury on corn. Symptoms include
a speckling of the leaf and browning on leaf tips and edges. Contact
injury will show on leaves that are emerged at the time of treatment
but not on new leaves emerging after treatment.

Plate 46. Bromoxynil injury on corn.
Acetolactase Synthase (ALS) and
Other Products Containing These or Similar Herbicides (e.g., nicosulfuron,
imazethapyr,
chlorimuron-ethyl)
Sulfonylurea (ALS) injury on corn often appears as a
"flash" on the leaf. Typically, corn outgrows this level
of injury. Symptoms can include a yellow discolouration of the leaves,
yellow flash on leaf (as shown), stunting of the plant, a delay in
plant development and crinkled leaves or bleaching near the whorl.
Onion-leafing or a purpling of stem or leaves may also occur. Some
ALS herbicides may also reduce the root mass by shortening lateral
roots. These herbicides should not be applied to corn that has been
treated with an organophosphorus insecticide due to the increased
risk of injury.

Plate 47. ALS injury on corn showing "flash"
on leaf.
Group 1 graminicide (ACCase) injury on corn appears
as intervenal chlorosis on newer leaves. Older leaves may show red
or purple. The growing point turns brown and dies. The top of the
plant can be easily pulled out of the whorl. New growth dies first,
such that the plant appears to take considerable time to die after
application.

Plate 48. Group 1 graminicide (ACCase inhibitors)
injury on corn.
Plate 49 shows a susceptible corn plant injured by glufosinate
ammonium herbicide adjacent to plants that are tolerant. Susceptible
plants turn yellow and die. Injury occurs within the first few days
after application.

Plate 49. Corn plants susceptible and tolerant
to glufosinate ammonium.
Glyphosate drift on corn causes yellowing in whorl (some
reddening on leaf edges) near the growing point. Leaves can become
twisted, and plants will become stunted or die. Injury may take 1-2
weeks to develop and is not reversible.
Updates on Corn: Herbicide Injury
No updates available at this time.
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Related links...
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