Herbicide injury from carotenoid pigment inhibitors including clomazone, fluridone, isoxaflutole, mesotrione, norflurazon, and others.
- White, pale yellow to pale green foliage on new shoot tips and leaves of sensitive plants.
- Occasional pink to purple margins as pigment loss occurs.
- Affected tissues and growing points may become necrotic over time.
- Reduced growth.
- Over time, new growth may resume normal appearance resulting in green young growth but older white foliage.
Plant Entry and Symptom Expression
Most carotenoid pigment inhibitors are foliar applied and symplastically translocated throughout the plant. Some can be soil applied but must be incorporated to avoid volatilization or photodegradation. Soil applied carotenoid inhibitors (such as norflurazon and clomazone) enter the plant through the mesocotyl or hypocotyl of germinating seedlings and translocate symplastically. Clomazone has a high potential for vapor drift resulting in non-targeted plant bleaching. Carotenoid synthesis inhibition leads to loss of chlorophyll. Less sensitive plants, may resume normal growth within weeks of exposure.
Carotenoid pigment inhibitor injury may be confused with symptoms from:
- Certain bacterial and fungal infections may cause bleaching of the growing points. For example, plants in the aster family can exhibit white growing points caused by Pseudomonas syringae pv. targets. This may be separated from carotenoid pigment inhibitor damage by the absence of symptoms on species from other plant families.
- Severe micronutrient deficiency, such as late stages of severe Fe deficiency may bleach tissues.
- Contact herbicides such as paraquat will bleach more rapidly than carotenoid pigment inhibitors and typically lead to rapid necrosis.
- Protoporphyrinogen oxidase (PPO) inhibitor such as acifluorfen shows tissue discoloration but bronzing appears rather than bleaching.
- Air pollution and car exhaust may cause white foliage. This can usually be distinguished by proximity to vehicle exhaust.
- Insect growth regulators have been shown to cause bleaching in sensitive greenhouse crops.
Herbicide Mode of Action Category
|WSSA – 11||WSSA – 12||WSSA – 28|
|HRAC – F3||HRAC – F1||HRAC – F2|
Applied Weed Science: Including the Ecology and Management of Invasive Plants (3rd Edition), Merrill Ross & Carol Lembi, pages 165, 170-172.
Publication date: Sept. 10, 2015
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