Fungicide Phytotoxicity on Soybean
Published: 12/01/2023
Fungicide phytotoxicity, also known as triazole injury, can occasionally occur on soybean following the application of a foliar fungicide that contains an active ingredient in the demethylation inhibitor (DMI), or triazole fungicide class (Fungicide Resistance Action Group (FRAC) 3). Several DMI active ingredients, including propiconazole, prothioconazole, and tebuconazole can induce this injury. Some fungicides containing thiophanate-methyl (or members of the methyl benzimidazole carbamates (MBC-FRAC 1)) can also cause minimal injury. It is unknown how the fungicide causes this injury, but symptoms are most likely to manifest in the upper canopy 21-28 days after application. The injury typically appears as interveinal chlorosis, characterized by the yellowing of tissue between the leaf veins. In severe cases, the leaf tissue between the veins may turn necrotic, or brown, and die. These symptoms can be mistaken for those of several soybean diseases, including red crown rot and sudden death syndrome (SDS).
Triazole injury on soybean.
Tom Allen
Triazole injury on soybean.
Tom Allen
The extent of injury can vary depending on the adjuvant rate, glyphosate formulation (if tank mixed with a DMI fungicide), environmental conditions, and variety selection. The specific DMI-active ingredient used can also influence the severity of phytotoxicity. Some DMI active ingredients can cause mild injury, resulting in limited interveinal chlorosis. This type of injury is most likely to occur with products that contain propiconazole (e.g., Tilt) or tetraconazole (e.g., Domark). More severe injury has been observed when products that contain prothioconazole (e.g., Delaro, Stratego YLD) are applied. Fungicide phytotoxicity can affect up to 50% of the leaves in a field. Although symptoms can be severe, yield loss due to fungicide phytotoxicity has not been reported.
Developed by Tom Allen, Mississippi State University.
Triazole injury on soybean. By Tom Allen.
Triazole injury on soybean. By Tom Allen.
Triazole injury on soybean. By Tom Allen.
Triazole injury on soybean. By Tom Allen.
Triazole injury on soybean. By Tom Allen.
Triazole injury on soybean. By Tom Allen.
Triazole injury on soybean. By Tom Allen.
Triazole injury on soybean. By Tom Allen.
Triazole injury on soybean. By Tom Allen.
Gallery images courtesy Tom Allen.
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