WSU Extension


Herbicide Damage : Horticultural spray oil
(revision date: 5/1/2013)

Horticultural spray oils may be applied to plants for control of various diseases, insects and mites. However, if oils are applied when temperatures are below 50 degrees F or above 85 degrees F, plant tissues may be damaged. In addition, oils should not be applied within 2 to 4 weeks of sulfur applications, or necrotic (dead) foliage may result. Symptoms may include chlorotic spots, general leaf chlorosis or yellowing, or leaf browning or loss. Horticultural oils also may remove the bluish color from blue spruces and other blue-needled conifers. Some plants with known potential for oil damage include palms, ferns, and some broadleaf evergreens.
Management Options

Non-Chemical Management
  • Do not apply horticultural spray oils during freezing weather.
  • Carefully read all label instructions and precautions prior to purchasing and applying horticultural spray oils.
Select non-chemical management options as your first choice!

Chemical Management

Carefully read all label instructions prior to using horticultural spray oils.

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Caption: White spruce horticultural spray oil damage
Photo by: R. Maleike
Caption: Blue spruce horticultural spray oil damage
Photo by: R. Maleike