What's Eating Your Garlic?

Allium sativum

Reviewed by Kiersten Rankel M.S.

Quick Answer

For garlic, the most likely culprits are onion thrips (silvery streaks running along the flat leaves) and onion maggot (fly larvae that bore straight into the bulb and ruin the harvest). Aphids show up rarely, mostly clustered on the central scape in spring. Garlic's strong sulfur compounds repel most other pests, which is why it's often planted as a companion deterrent for nearby crops.

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What does the damage look like?

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Soft rotting bulbs at harvest

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Silvery streaks along flat leaves

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Cluster of bugs on the scape

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Pests, ranked by impact

Small leaf weevil resting on a green leaf

Onion maggot

Damage

High

Removal

Hard

What it looks like

Small white legless fly larvae, 6 to 8 mm long, that tunnel into the underground bulb from the base plate. The adult is a slim gray fly, slightly smaller than a housefly, that lays eggs at the soil line near garlic and onion stems in spring.

What the damage looks like

Outer leaves yellow and wilt mid-season as the larvae feed on the bulb below. Pulled bulbs show soft rotting tunnels through the cloves and a stinking soft mass at the base plate. Damage is permanent and the bulb cannot be saved or stored. The harvest target is gone.

How to get rid of them

Option 1

Float row cover from planting through fly emergence

Lay lightweight floating row cover (Agribon AG-19 or Reemay, ~$25 for 50 feet) directly on the bed at fall planting.

Anchor the edges with soil, sandbags, or landscape staples every 18 inches. Garlic stays short enough that the cover can rest on the leaves without hoops.

Leave covered through spring fly emergence (April to early May in most zones). Pull the cover only after soil temperatures rise above 70F, when the fly's first generation is past.

Option 2

Rotate the bed at least 3 years away from any allium

Pupae overwinter in the soil where last year's garlic, onions, leeks, or shallots grew. Plant garlic in a bed that has not held any allium for 3 or more years. Same-bed replanting is the single biggest reason home growers lose a crop to onion maggot.

Option 3

Pull and bag any wilting plants immediately

If a plant yellows and wilts mid-season, pull it the same day. The larvae move from one bulb to the next through the soil. Bag the plant and put it in the trash. Do not compost. Removing infested plants early protects the rest of the bed for the season.

Thrips

Damage

Medium

Removal

Moderate

What it looks like

Tiny pale yellow to brown insects, 1 to 2 mm long, that hide deep inside the folds where the strap-shaped flat leaves wrap together near the soil. Hard to see without parting the leaves. Populations build fastest in hot dry weather from late May through July.

What the damage looks like

Silver or whitish streaks running along the length of the flat leaves, often with tiny black dots of frass inside the streaks. Heavy feeding bronzes whole leaves and reduces the bulb's final size. The bulb still forms but stores poorly and is smaller at harvest.

How to get rid of them

Option 1

Strong water blast every 3 days for 2 weeks

Hold a hose nozzle 12 inches from the leaves and spray hard into the leaf folds where thrips hide. Garlic leaves are tough and shed water well, so you can spray aggressively. Repeat every 3 days for 2 weeks. The fastest, cheapest fix and works without chemicals.

Option 2

Spinosad spray at dusk, every 7 days for 3 rounds

Mix spinosad (Monterey Garden Insect Spray or Captain Jack's Deadbug Brew, ~$15) per label rate.

Spray at dusk, getting the spray down into the leaf folds at the soil line where thrips cluster.

Repeat every 7 days for 3 rounds. Spinosad is approved for organic edibles and breaks down in 1 to 2 days.

Option 3

Overhead irrigation through the dry stretch

Thrips thrive in hot dry conditions. Switch from drip to overhead irrigation in the afternoon during a heat wave. The wet leaves disrupt feeding and slow population growth. Garlic's broad flat leaves shed water fast enough that disease risk stays low.

Aphids

Damage

Low

Removal

Easy

What it looks like

Tiny pear-shaped insects, 1 to 3 mm long, in shades of green, gray, or black. Rare on garlic because the sulfur compounds in the leaves repel them. When they appear, they cluster on the central scape (the curling flower stalk) in spring rather than on the leaves themselves.

What the damage looks like

A dense cluster of small soft-bodied insects on the scape, sometimes with a sticky shiny film below. The leaves stay clean. Damage is mostly cosmetic on the scape and does not affect the bulb. Most growers cut the scape off anyway to redirect energy back into the bulb.

How to get rid of them

Option 1

Cut the scape and bag it

If aphids cluster on a scape, cut the scape at the base and put it in the trash. Garlic scapes should come off in spring anyway to push more energy into the bulb. Removing the scape removes the entire aphid colony in one cut. Eat the scape if it's clean. Otherwise discard.

Option 2

Strong water blast if the leaves are affected

If aphids spread off the scape onto the leaves, hold a hose nozzle 12 inches away and spray hard. Garlic's tough strap-shaped leaves take the pressure well. One or two blasts a few days apart usually clears the infestation completely.

Stay ahead of all of them

Four habits that keep garlic pest pressure rare and the bulbs sound at harvest.

Rotate at least 3 years away from any allium

Onion maggot pupae overwinter in the soil under last year's garlic, onions, leeks, and shallots. Plant garlic in a bed that has held no allium crop for 3 or more years. Same-bed replanting is the single biggest reason home garlic crops fail.

Float row cover from planting through fly emergence

Lay lightweight row cover on the bed at fall planting and leave it through spring fly emergence in April to early May. Garlic stays short enough that the cover rests directly on the leaves with no hoops. The cover blocks every adult onion maggot fly before it can lay eggs.

Plant garlic as a companion deterrent for other crops

Garlic's sulfur compounds repel aphids, cabbage moths, and many other soft-bodied pests. Tuck cloves between carrots, brassicas, and roses for a passive pest barrier. The garlic protects the neighbors and uses no extra space in the bed.

Harvest before the bulbs over-mature

Pull garlic when about half the lower leaves have turned brown and the rest are still green, usually early to mid summer in most zones. Bulbs left in the ground past this point split, lose their wrappers, and become attractive to onion maggot for the next generation.

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About This Article

Kiersten Rankel M.S.

Botanical Data Lead at Greg · Plant Scientist

About the Author

Kiersten Rankel holds an M.S. in Ecology & Evolutionary Biology from Tulane University. A certified Louisiana Master Naturalist, she has over a decade of experience in science communication, with research spanning corals, cypress trees, marsh grasses, and more. At Greg, she curates species data and verifies care recommendations against botanical research.

See Kiersten Rankel's full background on LinkedIn.

Editorial Process

Pest identification and treatment guidance verified against Allium sativum field reports from Greg's botanical database, cross-referenced with university extension sources and published horticultural research.

930+ Greg users growing this plant

USDA hardiness zones 3a–9b

Citations:
NC State Extension
Aphid photo: Scot Nelson (CC0)
Beetle placeholder: Prasan Shrestha (CC BY-SA 4.0)
Thrips photo: Ryan Hodnett (CC BY-SA 4.0)