White Powder on Mulberry: Bark Lice or Powdery Mildew?

Two Very Different Culprits

A white coating on mulberry trunks and branches is often bark lice—tiny, harmless insects that spin silken webs for protection while they graze on fungi, lichens, and dead insects. They don’t damage the tree.

If the white powder is on the leaves and small stems, it’s likely powdery mildew, a fungal disease that forms superficial white to gray patches. Severe infections can yellow and brown leaves, but on many trees it’s mostly cosmetic.

What to Do

• Bark lice: No treatment needed. If webs are unsightly, blast them off with a strong water jet or spray 2 tbsp liquid dish soap per gallon of water.
• Powdery mildew: On small plants, apply labeled fungicides (e.g., triadimefon, triforine, thiophanate-methyl, propiconazole) at first sign, repeating on a schedule. On large trees, spraying is impractical; the disease rarely threatens tree health.

Proper identification—by examining where the powder occurs—saves time and unnecessary spraying.