The following herbicide injury diagnostic key uses a three-step approach to separate our numerous herbicides into eleven modes of action. Then, the herbicides within a mode of action can be investigated further to determine if one of them caused the injury. The first step in the key is to determine when the injury symptoms first became evident; symptoms appearing during or immediately after crop emergence may indicate carry-over or preemergence herbicide injury while symptoms appearing after crop emergence points to a postemergence herbicide. The second step is to determine if the injury was the result of a herbicide with contact activity or if the herbicide was translocated in the plant. A contact herbicide affects the leaves that were treated while a translocated herbicide affects new leaves. The final step in the key is to match the injury symptom to a herbicide mode of action. The following table lists many of the most common situations that lead to crop injury.
Injury Symptoms Appear:
During or immediately after crop emergence
• Herbicide carry-over
• Misapplication- rate too high
• Shallow seed placement
• Wrong herbicide rate for soil type
• Improper interval between herbicide application and planting
• Excessive rainfall and cold soils
• Improper herbicide placement or timing
After crop emergence
• Drift
• Tank contamination
• Misapplication- rate too high
• Incorrect additive/surfactant
• High temperatures/humidity at application
• Improper tankmix partner
• Wrong herbicide
• Did the herbicide injury appear
• During or immediately after crop emergence
The initial crop stand was not uniform or the plants lacked vigor.
•
After crop emergence
Initial crop stand was uniform, plants vigorous.
•
Selectivity: Check weeds and crops to determine selectivity
Other factors that mimic herbicide injury
Not all crop injury is the result of herbicide use. One of the more difficult tasks in diagnosing plant injury is to recognize that factors other than herbicides can produce injury symptoms. The following list provides many of the more common factors that produce injury symptoms that mimic herbicide injury.
Glufosinate mimics
• Corn
o layby anhydrous ammonia application
o frost
o heat scald
• Soybeans
o frost
o iron chlorosis
• Consider these herbicide modes of action
• Pigment Inhibitors
Plants have white, bleached leaves.
Grass species are more sensitive than broadleaves.
•
more
Leaves have chlorotic veins, margins, or tips or necrotic margins.
Broadleaves are generally more sensitive that grasses.
•
more
Plants have deformed leaves.
•
•
•
• Consider these herbicide modes of action
• Growth Regulators
Grass leaves tightly roll (onion leafing).
Broadleaves exhibit leaf cupping and strapping.
The stems of both grasses and broadleaves may twist (epinasty).
Broadleaves are more sensitive than grasses.
•
Seedling Shoot Growth Inhibitors
Grass plants leaf-out before emergence. Grasses exhibit improper lea
1. Herbicide Injury Diagnostic Key
Herbicide Injury Diagnostic Key
T. L. Trower and C. M. Boerboom
The following herbicide injury diagnostic key uses a three-step approach to separate our
numerous herbicides into eleven modes of action. Then, the herbicides within a mode of action
can be investigated further to determine if one of them caused the injury. The first step in the
key is to determine when the injury symptoms first became evident; symptoms appearing during
or immediately after crop emergence may indicate carry-over or preemergence herbicide injury
while symptoms appearing after crop emergence points to a postemergence herbicide. The
second step is to determine if the injury was the result of a herbicide with contact activity or if
the herbicide was translocated in the plant. A contact herbicide affects the leaves that were
treated while a translocated herbicide affects new leaves. The final step in the key is to match
the injury symptom to a herbicide mode of action. The following table lists many of the most
common situations that lead to crop injury.
Injury Symptoms Appear:
During or immediately after crop emergence
Herbicide carry-over
Misapplication- rate too high
Shallow seed placement
Wrong herbicide rate for soil type
Improper interval between herbicide application and planting
Excessive rainfall and cold soils
Improper herbicide placement or timing
After crop emergence
Drift
Tank contamination
Misapplication- rate too high
Incorrect additive/surfactant
High temperatures/humidity at application
Improper tankmix partner
Wrong herbicide
Did the herbicide injury appear
During or immediately after crop emergence
The initial crop stand was not uniform or the plants lacked vigor.
2.
After crop emergence
Initial crop stand was uniform, plants vigorous.
Selectivity: Check weeds and crops to
determine selectivity
Root development is normal
but the plants are stunted and have damaged leaves.
3. Root development is abnormal;
the leaves do not usually exhibit injury symptoms.
Location of injury on the plant
Treated leaves injured, new growth unaffected.
This indicates a Contact herbicide.
New leaves (meristem) injured, older leaves unaffected.
This indicates a Translocated herbicide.
4. Consider these herbicide modes of action
Photosynthesis Inhibitors
PPO Inhibitors
Consider these herbicide modes of action
Bipyridiliums
Plants suddenly develop lesions on exposed leaves,
lesions gradually appear water-soaked then become necrotic.
Leaf speckling may be caused by drift.
5. Glufosinate
Plants gradually turn yellow then die.
Mode of Action: membrane disruption
Glufosinate inhibits the activity of the glutamine synthetase enzyme, which causes
ammonia build-up in the cell. The ammonia destroys cell membranes.
Corn injury photo gallery
Soybean injury photo gallery
Other factors that mimic injury
Herbicide families and examples
Glufosinate: Corn Injury Photo Gallery
Liberty applied to non-Liberty Link and Liberty Link varieties.
6. Liberty applied to non-Liberty Link variety.
Liberty applied to non-Liberty Link variety.
8. Other factors that mimic herbicide injury
Not all crop injury is the result of herbicide use. One of the more difficult tasks in diagnosing
plant injury is to recognize that factors other than herbicides can produce injury symptoms. The
following list provides many of the more common factors that produce injury symptoms that
mimic herbicide injury.
Glufosinate mimics
Corn
o layby anhydrous ammonia application
o frost
o heat scald
Soybeans
o frost
o iron chlorosis
Consider these herbicide modes of action
Pigment Inhibitors
Plants have white, bleached leaves.
Grass species are more sensitive than broadleaves.
more
Leaves have chlorotic veins, margins, or tips or necrotic margins.
Broadleaves are generally more sensitive that grasses.
9.
more
Plants have deformed leaves.
Consider these herbicide modes of action
Growth Regulators
Grass leaves tightly roll (onion leafing).
Broadleaves exhibit leaf cupping and strapping.
The stems of both grasses and broadleaves may twist (epinasty).
Broadleaves are more sensitive than grasses.
Seedling Shoot Growth Inhibitors
Grass plants leaf-out before emergence. Grasses exhibit improper leaf unfurling during
10. emergence that leads to buggy whipping. Broadleaf plants are stunted, have reduced
stands, and leaves have a draw-string (caused by shortened leaf midribs)
appearance. Grasses are more sensitive than broadleaves.
Mode of Action: growth regulator
The concentration of the synthetic auxin herbicide determines the response of the
plant. Low concentrations stimulate rapid cell division and growth, resulting in vascular
tissue destruction. Higher concentrations inhibit cell division and growth, usually in the
meristematic regions.
Several of the synthetic auxin herbicides are very susceptible to off-target movement and
care should be taken with their use.
Mode of Action: seedling shoot growth
inhibition
The site of action is unknown. Both chloroacetamide and thiocarbamate herbicides
inhibit the synthesis of fatty acids and proteins.
