Garlic Diseases and Pests: White Rot, Rust, Onion Fly and More

The most serious garlic problem is white rot, a soil fungus that can persist for 20 years. More common in gardens are rust (orange spots on leaves in humid weather) and pests such as onion maggots, thrips and, in Europe, the leek moth. Crop rotation and clean seed garlic prevent most issues.

Diseases

• White rot: yellowing, dying leaves and fluffy white growth with tiny black specks on the bulb. No cure; do not grow alliums in that soil for many years.
• Rust: orange pustules on leaves; worse in damp, crowded beds. Space plants, avoid overhead watering, remove affected leaves.
• Downy mildew: pale, greyish patches in cool, wet weather.
• Fusarium basal rot: roots and base rot, often in warm soils.
• Penicillium decay: blue-green mould on stored or damaged cloves.

Pests

• Onion maggot / onion fly: larvae tunnel into bulbs; use fleece covers in spring.
• Thrips: silvery streaks on leaves in hot, dry weather.
• Leek moth: caterpillars mine leaves and stems; cover with fine mesh.
• Bulb and stem nematode: swollen, distorted plants; destroy infected stock.

Prevention

• Rotate: do not plant garlic, onions or leeks in the same spot for 3–4 years.
• Plant healthy, certified seed garlic.
• Ensure good drainage and spacing.
• Harvest and cure promptly.

More Garlic Guides

• How to Grow Garlic: The Complete Guide
• When to plant garlic by zone
• Hardneck vs softneck garlic and varieties
• How to plant garlic cloves

Frequently Asked Questions

What are the orange spots on my garlic leaves?

Garlic rust, a fungal disease of humid weather.

What causes garlic to rot in the ground?

Waterlogged soil, white rot or fusarium basal rot.