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

On this page
  • Armyworms
  • Loopers
  • Corn earworm
  • Leafminer
  • Green peach aphids
  • Anthracnose
  • Lettuce drop
  • Corky root
  • Tomato spotted wilt
  • Ammonium toxicity
  • Big vein
  • Fusarium wilt
  • Downy mildew

See also, pests of other regions: Central Coast 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
Identification tip: Armyworm 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 damage
Identification tip: As larvae mature they develop distinct stripes, but the overall color is variable.

Leafminer damage
Leafminer damage
Identification tip: Larvae mine between upper and lower leaf surfaces, creating winding, whitish tunnel.

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

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.

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.

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.
Ammonium toxicity
Ammonium toxicity
Identification tip: Discolored vascular tissue caused by ammonium toxicity.
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.
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.
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.

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