Leaf spots can have different causes, including pests and growing conditions. Check both leaf surfaces and recent care before choosing a product.
A spot is an observation, not a diagnosis
Look at both sides of an affected leaf and compare nearby foliage. Record the size, texture and position of marks, including whether they rub off. Take photographs before making changes so you can see whether new damage is appearing.
Check the growing history
Recent sprays, a move into stronger sun, wet roots and pests can produce different kinds of leaf damage. Check what changed before symptoms began. A white mark does not automatically establish that a plant has a particular fungal disease.
Choose action from the cause
Keep a plant apart while investigating a possible pest problem. Use plant-specific guidance or an identification service where needed. If a treatment product is appropriate, follow its label rather than combining several products because leaves look spotted.
Related reading: Plant Problems Linked to Growing Conditions.