White Spots on Meyer Lemon: Powdery Mildew or Insect Infestation?

White specks on Meyer lemon leaves—especially when accompanied by a frothy, foamy substance at leaf joints—can indicate either a fungal disease like powdery mildew or an insect problem such as mealybugs or scale.

Distinguishing the Cause

• Powdery mildew: Appears as a light, white dusting on leaf surfaces, often in blotches. Favored by humid conditions and cool nights. May cause leaf deformation and dark spores in severe cases.
• Insects (mealybugs, scale, whiteflies): Juvenile stages look like tiny white flecks. They cluster at leaf crotches and produce honeydew, which can look foamy. Look for cottony masses or sticky residue.

Immediate Actions

1. Inspect closely with a magnifying glass. Check leaf undersides and stems.
2. If insects are present, spray with insecticidal soap or neem oil, covering all surfaces.
3. If powdery mildew is suspected, apply a sulfur-based or potassium bicarbonate fungicide.
4. Improve air circulation and avoid overhead watering.

Risk to Nearby Plants

Both powdery mildew and many citrus pests can spread to neighboring plants like jasmine. Isolate the lemon tree if possible and treat promptly.