Onion White Powder on Leaves: Causes & How to Fix It

Check these first

• Does it rub off with a finger? Powder that rubs off is a fungus; marks that stay are scarring from pests.
• Is it on the upper or lower leaf surface, or concentrated on new shoots and leaf joints?
• If it is cottony, look inside the fluff for insects.

Most likely causes

From the pests and diseases recorded for this plant, the ones whose symptoms match, most serious first. Symptoms alone rarely confirm a cause, so use the linked page to check the signs and treatment.

Other possible causes

• Sclerotinia Rot — The crown, stem or head rots in a water-soaked way and is covered in white cottony myceliu…
• Rust — Small raised orange-yellow to red-brown pustules form on both leaf surfaces, then rupture …

Other symptoms on this plant

What other growers did about it

A page like this one can tell you what onion white powder on leaves is and what to try. What it cannot tell you is what actually happened to someone who had it on the same plant, at the same point in the season, and what they did next.

Gadenin is a free garden journal built around that. You photograph the plant, tag what you are seeing, and the entries line up by date for each plant you grow.

• Tag the problem and the app tells you how many other growers have logged the same thing on the same plant.
• Growers who make their records public can be followed, so you can read what they did and how it turned out.
• Next season your own entries come back at the same point in the year, so you check the plant before it starts.

Written byYasuGrowing vegetables and fruit in Chiba, Japan, and building Gadenin. Corrections are welcome. 15 years of growing.