White rot is a fungal disease that attacks the roots and base of the plant. Infected plants yellow and wilt as the roots begin to decay. White, fluffy fungal growth develops around the bulb or lower stem, followed by tiny hard black structures called sclerotia.

The sclerotia can survive in the soil for many years, remaining dormant until susceptible plants are grown nearby.

How to Fix It

Remove and destroy infected plants, including as much of the root system and surrounding soil as practical. Do not compost them. Clean soil and plant debris from tools before using them elsewhere in the garden.

White rot is extremely difficult to eliminate once established because the sclerotia can survive in soil for many years. Avoid planting onions, garlic, leeks and other alliums in the affected area. Long crop rotations help reduce risk, but ordinary short rotations are not enough for heavily contaminated soil.

Start with healthy, disease-free planting material and avoid moving contaminated soil, bulbs or equipment into clean areas. Good drainage helps reduce disease development, but it will not eliminate white rot once the pathogen is present.

Biological controls are limited. Some beneficial fungi, including Trichoderma species, can suppress white rot under certain conditions, but they are not a reliable cure for heavily infested garden soil. Prevention and sanitation remain the most effective controls.