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Lettuce

Pests and their Damage—Rosette to Heading (Central Coast)

On this page
  • Armyworms
  • Cutworms
  • Corn earworm
  • Loopers
  • Saltmarsh caterpillar
  • Silveleaf whitefly
  • Corky root
  • Lettuce dieback
  • Fusarium wilt
  • Big vein
  • Lettuce drop
  • Lettuce mosaic
  • Downy mildew
  • Anthracnose
  • Bottom rot
  • Ammonium toxicity
  • Powdery mildew
  • Lettuce chlorosis
  • Tomato spotted wilt
  • Varnish spot

See also, pests of other regions: Central Valley and Desert.

Check for stand uniformity and wilted plants and inspect plants for pests and pest damage. Names link to more information on identification and management.

Click on photos to enlarge

Beet armyworm larva feeding on lettuce crown
Beet armyworm larvae
Identification tip: Newly hatched larvae are small, green worms that often feed in groups.

Larva of the armyworm
Armyworm
Identification tip: Larvae are variable in color but are usually dark green or gray, with three thick stripes running down each side.

Adult cutworm
Cutworms
Identification tip: Larvae frequently roll into a C-shape when disturbed.

Adult cutworm
Corn earworm damage
Identification tip: As larvae mature they develop distinct stripes, but the overall color is variable.

Looper damage to lettuce
Looper damage
Identification tip: Larvae feed primarily on the undersides of lower leaves, skeletonizing them and contaminating them with frass.

Saltmarsh caterpillar
Saltmarsh caterpillar
Identification tip: Early instars are various shades of yellow-brown with long, dark hairs.

Silverleaf whitefly
Silverleaf whiteflies
Identification tip:
Adults are tiny 0.06 inch (1.5 mm) long, yellowish insects with white wings.

Corky root
Corky root damage
Identification tip:  Roots show reduced feeder roots and a rough, pitted taproot.

Lettuce dieback
Lettuce dieback
Identification tip: Outermost leaves are extensively yellowed. The younger, inner leaves often remain dark green in color but can be rough and leathery in texture.

No photo available.

Fusarium wilt
Identification tip: Leaves turn yellow and develop tipburn. The vascular system is brown to black in the leaves and a reddish brown discoloration develops in the cortex of the crown and upper root. Plants may be stunted and fail to form heads.

Big vein
Big vein damage
Identification tip: Veins in leaves become enlarged and clear; easily seen if leaf is examined with the light source behind it. Enlarged veins cause the rest of the leaf to be ruffled and malformed.

Lettuce drop causes the older leaves to wilt.
Lettuce drop

Identification tip: Older leaves wilt; eventually the entire plant wilts and collapses, making it unharvestable.

Lettuce mosaic
Lettuce mosaic
Identification tip: Symptoms of lettuce mosaic vary greatly based on the lettuce variety and the stage of lettuce at time of infection. One symptom is the development of a mottling pattern on leaves.

Downy mildew
Downy mildew damage
Identification tip: Light green to yellow angular spots develop on the upper surface of the leaf.

Downy mildew
Downy mildew damage
Identification tip: Underneath the leaf, immediately below these angular spots, white fluffy fungal masses grow. With time lesions turn brown and dry up.

Anthracnose
Anthracnose damage
Identification tip: Small, water-soaked spots (less than 3 mm) on outer leaves eventually enlarge, turn yellow, and become irregular and angular in shape.

Anthracnose
Bottom rot (Rhizoctonia diseases)
Identification tip: Brown sunken lesions form on midribs in contact with soil. Lesions may expand to rot lower leaves.

Ammonium toxicity
Ammonium toxicity
Identification tip: Discolored vascular tissue caused by ammonium toxicity.
Powdery mildew
Powdery mildew damage
Identification tip: Appears as a white, powdery growth on both upper and lower sides of lettuce leaves.
Powdery mildew
Powdery mildew damage
Identification tip: Severe powdery mildew infection on iceberg lettuce.
Lettuce chlorosis
Lettuce chlorosis
Identification tip: Symptoms of lettuce chlorosis and lettuce infectious yellows are virtually identical. Leaves exhibit severe yellowing, rolling, brittleness, and vein-clearing.
Tomato spotted wilt virus
Tomato spotted wilt
Identification tip: Iceberg lettuce develops necrotic lesions on leaves.
Varnish spot damage
Varnish spot (Pseudomonas cichorii) damaged head
Identification tip: Leaves exhibit dark brown spots that are firm and shiny.
 

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