Onion and Garlic Photo Guide

Adult leafminer

Identification tip: Leafminers that attack onion and garlic are small, black-and-yellow flies.

Leafminer larvae or pupa

Identification tip: Larvae are white to yellow, legless, 0.11 to 0.15 inch (2.8–3.81 mm) long, and tunnel within onion and garlic leaves. Pupae are dark brown, and may either be in the soil or on the plant.

Leafminer damage

Identification tip: Larvae mine inside the leaf, creating winding, whitish tunnels.

Adult seedcorn maggot fly

Identification tip: Adults of both maggot species are small, gray flies.

Maggot pupa and larvae

Identification tip: Larvae are creamy-white, legless, and about 0.4 inch long.

Onion maggot damage

Identification tip: Both seedcorn maggot and onion maggot feed on roots and the developing stem, but onion maggot can also continue to feed on the expanding bulb.

Acarid mite adults and eggs

Identification tip: Shiny, creamy-white, bulbous mites that range from 0.02 inch to 0.04 inch long. They look like tiny pearls with legs.

Eriophyid mite damage

Identification tip: Feeding by eriophyid mites produces sunken brown spots and streaks on garlic cloves.

Thrips

Identification tip: Thrips are small, slender insects. When viewed with a hand lens, they can be identified by their two pairs of wings with fringed with long hairs.

Thrips feeding

Identification tip: Thrips feed under the leaf folds and in the protected inner leaves near the bulb by scraping the plant surface and sucking the juice.

Thrips scarring

Identification tip: Scarring of leaves on green onions.

Botrytis leaf blight

Identification tip: Small (0.06 to 0.25 inch), white, sunken spots on leaves. Spots may have light green halos or may appear water-soaked.

Center rot

Identification tip: Yellow flagging of the young leaves.

Downy mildew

Identification tip: Fine, furry, grayish-white to purple growth on the surface of older leaves. Leaf tissue under the growth becomes pale green, then yellow, then collapses.

Garlic mosaic

Identification tip: Small, angular, light-green-to-yellow, discolored regions of leaf tissue arranged in a mosaic pattern among darker tissue, striping and streaking of leaves, and irregularly shaped, light green blotches among normally colored tissue.

Iris yellow spot virus

Identification tip: Yellow to straw-colored lesions on onion leaves and scapes.

Onion yellow dwarf virus

Identification tip: Yellow streaks at the base of the first leaves. Later, yellow streaking to complete yellowing of leaves.

Onion yellow dwarf virus

Identification tip: Yellow leaf streaks and crinkled leaves.

Purple blotch and Stemphylium leaf blight

Identification tip: Oval-shaped, tan and deep purple lesions on leaf blades. Lesions may have concentric (target-shaped) zones. Yellow or brown streaks extend from the lesion that extend along the blade in both directions.

Rust on garlic

Identification tip: Small, oval- or diamond-shaped, reddish to dull-orange pustules on leaves. Later in the growing season, the lesions may appear dark because black spores develop within the pustules.

Bacterial soft rot

Identification tip: Softening and water-soaking of one or more of the inner fleshy scales of the bulb. Affected tissue is initially yellow and turns brown as the disease progresses. The neck of infected bulbs may be soft when pressed.

Black mold

Identification tip: Water-soaked areas of scales that become dry and shrivel under dry conditions. Visible black masses of spores on the outer scales.

Blue mold

Identification tip: Water-soaked areas of the outer surface of scales that can later develop a green to blue-green, powdery mold. Generally appears between harvest and storage.

Botrytis neck and bulb rot on onion

Identification tip: Generally appears during storage. The neck tissue initially softens, becomes water-soaked, and turns brown. In humid environments, a gray, feltlike growth appears on rotting scales, and mycelia may develop between the scales. Generally appears during storage.

Fusarium basal rot

Identification tip: When cut vertically, a brown discoloration is apparent on the basal plate. The stem plate later becomes pitted and shows a dry rot. The stem plate and outer scales may crack open under dry conditions.

Pink root

Identification tip: Infected roots first turn light pink, then become darker red to purple, shrivel, turn black, and die. Pinkish-red discoloration may extend up into the outer scales of the bulb.

Sour skin

Identification tip: A horizontal cross-section of the bulb may reveal a tan-colored, slimy ring. The neck of infected bulbs is soft when pressed.

Southern blight

Identification Tip: Outer leaves turn yellow and wilt. The bulb and base of the leaves are affected by a soft rot. A white mycelium, often growing in a fanlike pattern, is present on the bulb and in the soil. Numerous tan to reddish-brown sclerotia are present in the soil.

White rot

Identification tip: A fluffy, white growth (the fungal mycelium) develops around the base of the bulb. As the disease progresses, the mycelium becomes more compacted, and small spherical black bodies (sclerotia) the size of poppyseeds develop in it.

Stem and bulb nematode damage
Identification tip: Bulb tissue begins softening at the neck and progresses downward. Scales appear gray, and under dry conditions the bulbs dessicate and split at the base.

Stubby root nematode damage

Identification tip: Stubby root nematode feeding causes roots to be extremely short with a yellow or brownish cast.

Root-knot nematode damage

Identification tip: Feeding by this nematode induces the development of root knots (galls) that can be seen with the naked eye.