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Herbicide Residual Injury on Canola Residue Symptoms on True Leaves - Herbicides - Crop Production - Canola - Plant & Soil Sciences

RESIDUE SYMPTOMS ON TRUE LEAVES

MILD SYMPTOMS Mild injury involves minimal or no damage to the meristem, but can interfere with early leaf development. Mild injury may not produce sufficient symptoms for definite diagnosis until the 3-leaf stage since symptoms may mimic nutrient deficiency or cold stress. Maturity delay can occur with mild injury. Mild symptoms (A) can include mild chlorosis noticeable on the 1st and 2nd leaves, reduced leaf area and mild cupping of the 3rd leaf. After two weeks, (B) leaf size was normal and no other symptoms were evident. Plant development was delayed by two leaf stages relative to nearby plants.
An unaffected plant (left) and one with chlorosis and reduced leaf size (right). The 1st and 2nd leaves show the initial injury through reduced leaf area and elongated petioles. Petiole elongation is typical of mild injury.
Differences between uninjured (left) and injured (right) plants could not be seen until the 3-leaf stage.
SEVERE SYMPTOMS Severe symptoms are characterized by meristematic damage which may result in; 1) poor recovery and subsequent maturity delay, 2) yield loss, or 3) plant death Other symptoms may include early and long lasting purpling or chlorosis, cupping, reduction in leaf area and very slow growth. Severe injury is not mimicked by nutrient, insect or disease injury symptoms. Severe chlorosis, purpling and cupping (1) and a normal plant (2).
At the 3-leaf stage (A), unaffected (left) and severely affected (right) plants. Affected plants have chlorotic cotyledons with minimal 1st leaf growth.
After four weeks of growth (B), there was minimal leaf recovery.
At the 2-leaf stage (A), severe symptoms include growth reduction, purpling and cupping. After three weeks (B), symptoms were still present.
After six weeks (C), symptoms have diminished, but leaves are chlorotic and small.
Leaf purpling and cupping on the 1st (yellow arrow) and 2nd leaf (red arrow) are classic injury symptoms. Although plants can recover, this level of injury slows plant development.
Another classic symptom is leaf chlorosis. Both the 1st and 2nd leaves have overall chlorosis. Chlorosis was observed through the 4-leaf stage.
The first leaf is almost unrecognizable (red arrow). The production of the colorless leaf buds (yellow arrow) indicates a residue effect. This plant is unlikely to flower.
An example of severe chlorosis. Leaves can appear almost transparent.
The combination of severe chlorosis and significant leaf area reduction indicates substantial herbicide carryover (A). Inset: an unaffected plant the same age.
After six weeks, plants still exhibit symptoms: elongation and thickening of leaf petioles, mottled leaf chlorosis and reduced leaf area (B).
This level of meristem damage causes premature growth of side branches (A). Inset: an unaffected plant the same age.
After five weeks, these plants are still chlorotic and stunted (B).