Risk of Spraying Pesticides to tree foliage at Extreme Temperatures

People often apply pesticides to trees in leaf to protect the leaves from insect or disease damage. Unfortunately, pesticides can sometimes burn the foliage if applied when the air temperature is too high.  Typically, any temperature above 85 degrees Fahrenheit are considered a risk when apply pesticides directly to the foliage.  The higher than optimum temperature exaggerates the pesticides penetration of the leaf cuticles, negatively affecting the tree’s cellular processes. This can result in a burning or scorching of the leaf tissue.

Special care in particular should be taken with fruit trees when applying insecticide spray oils to the foliage. In addition to the above, leaf/fruit spots, blotches, scorch and tip burn can occur if the weather is dry and soil moisture along with humidity is low.

So, in conclusion, the ‘take home message’ is always apply pesticides with caution. It should be below 85 degrees Fahrenheit when applying to the foliage, plus observe any other recommendations on the pesticide’s label for a successful application of product.

Harold Hoover, Board Certified Master Arborist


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