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4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting (herbicide group [HG] 27) herbicides are commonly referred to as the ‘bleacher’ herbicides. The HPPD-inhibiting herbicides inhibit plant pigment synthesis, which results in chlorosis and/or bleaching of vegetative tissue (Figure 1). Symptomology exhibited by treated plants may range from bleaching of the leaf margins to the entirety of the leaf. The HPPD-inhibiting herbicides are phloem mobile, resulting in injury being seen on new growth.

Injury incurred by the HPPD-inhibiting herbicides on soybeans can be transient if the doses are low or can result in plant death if the doses are high. Injury to soybeans can occur from physical drift or carryover from previous growing seasons. When a soybean plant emerges with bleached or chlorotic cotyledons and true leaves, the injury is likely from HPPD-inhibiting herbicide carryover. When injury to a soybean plant is when trifoliates are bleached and the injury severity decreases across the field, the injury is likely from HPPD-inhibiting herbicide drift. Injury caused by HPPD-inhibiting herbicides can be confused with injury caused by clomazone (HG 13). Clomazone is also referred to as a ‘bleacher’ herbicide that is applied pre-emergence. Injury caused by HPPD-inhibiting herbicides and clomazone are almost indistinguishable (Figure 2). However, injury caused to soybeans by clomazone will subside with time.

HPPD-inhibiting herbicide pre-emergence

Figure 1. HPPD-inhibiting herbicide injury on soybean applied pre-emergence.

Post emergence HPPD-inhibiting herbicide injury

Figure 2. HPPD-inhibiting herbicide injury on soybean applied post-emergence.

Clomazone injury on soybeans pre-emergence applied

Figure 3. Pre-emergence application of Clomazone injury on soybeans

Author

Extension Weed Specialist and Associate Professor
Crop & Soil Sciences

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Publication date: Dec. 3, 2020

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N.C. Cooperative Extension prohibits discrimination and harassment regardless of age, color, disability, family and marital status, gender identity, national origin, political beliefs, race, religion, sex (including pregnancy), sexual orientation and veteran status.