Onion Thrips

Symptoms by part

Causes

• Hot and dry weather conditions.
• Nearby weeds that serve as alternative hosts for the insects.
• High nitrogen fertilization which encourages succulent growth that thrips prefer.

Could be confused with

• Powdery Mildew · Powdery mildew creates a fuzzy white fungal growth that can be wiped off, whereas thrips damage is a permanent scarring of the leaf tissue.
• Spider Mite damage · Spider mites create fine webbing between leaves and cause a stippled yellow appearance, while thrips leave distinct silvery streaks and dark fecal spots.

Treatment

1. 1. Use a strong stream of water from a hose to physically wash the insects off the leaves during the early morning.
2. 2. Apply fatty acids to the foliage, ensuring you cover both the tops and undersides of the leaves, follow the label.
3. 3. Use spinosad as a targeted spray on the foliage if the infestation remains heavy, follow the label.

Without chemicals

• Remove and destroy heavily infested leaves to reduce the population.
• Use reflective mulches like silver plastic around the base of plants to deter thrips from landing.
• Keep the surrounding area free of weeds that act as alternate hosts.
• Encourage natural predators like lacewings and ladybugs in your garden.

Chemical options

• Fatty acids, spray directly onto the insects, follow the label.
• Spinosad, apply to foliage when insects are present, follow the label.

Preventing it

• Rotate your crops annually to prevent thrips from establishing in the same soil.
• Use overhead irrigation to increase humidity around the plants, as thrips thrive in dry conditions.
• Plant trap crops like marigolds nearby to attract predators.
• Avoid excessive nitrogen fertilizer that creates soft, attractive growth.

When to act

Act as soon as you see the first silvery streaks on the foliage to prevent the population from exploding. If the entire crop is severely stunted and the leaves are dying back prematurely, it is best to remove the plants and dispose of them in the trash rather than the compost.

Questions people ask

Can I eat onions that have had thrips?

Yes, you can safely eat the bulbs. Simply peel away the damaged outer layers of the onion or garlic, as the thrips primarily feed on the green foliage.

Do thrips survive the winter?

Yes, they often overwinter in plant debris, soil, or on weeds, which is why cleaning up your garden beds at the end of the season is so important.

Plants it affects

• Ail
• Chives
• Leek
• Onion
• Welsh onion