Pests and their Damage—Heading to Harvest (Central Valley)

On this page
  • Armyworms
  • Loopers
  • Corn earworm
  • Green peach aphids
  • Botrytis crown rot
  • Big vein
  • Lettuce dieback
  • Powdery mildew
  • Lettuce drop
  • Tip burn
  • Anthracnose
  • Corky root
  • Lettuce chlorosis
  • Tomato spotted wilt
  • Varnish spot

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

Beet armyworm larva feeding on lettuce crown
Identification tip: Larvae are variable in color but are usually dark green or gray, with three thick stripes running down each side.

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

Color variations of tomato fruitworm
Corn earworm
Identification tip: As larvae mature they develop distinct stripes, but the overall color is variable.

Green peach aphids
Green peach aphids
Identification tip: Green peach aphids are dark green to yellow and have no waxy covering.

Crown damaged by Botrytis rot
Botrytis rot damage
Identification tip: Damaged heads show gray spores on wilted, outermost leaves.

Tip burn damage
Tip burn (warm weather)
Identification tip: Leaf tips turn brown.

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 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.

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.

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

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.

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

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.
Powdery mildew
Lettuce chlorosis
Identification tip: Symptoms of lettuce chlorosis and lettuce infectious yellows are virtually identical. Leaves exhibit severe yellowing, rolling, brittleness, and vein-clearing.

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Statewide IPM Program, Agriculture and Natural Resources, University of California
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