WE USE A SULFUR BASED FOLIAR SPRAY IN OUR IPM REGIMEN
If you notice a white or yellow residue in the grooves or spots on the leaves of your new plants, it's most likely dried foliar spray, not powdery mildew (PM).
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Sulfur is commonly used across many agricultural industries worldwide because it's one of the most cost-effective and efficient treatments for a variety of issues. This is why the presence of sulfur residue on your plants is perfectly normal.
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In fact, sulfur is so effective that it eliminates PM on contact. If you're dealing with powdery mildew, a sulfur treatment will take care of it.
Important Note: To avoid a potential phototoxic reaction, wait 7-10 days after a sulfur application before using any oil-based IPM treatments.