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Lettuce

Pests and their Damage—Rosette to Heading (Desert)

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

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

Check for stand uniformity and wilted plants and inspect plants for pests and pest or abiotic 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.

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.

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

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.

Lettuce drop causes leaves to die.
Lettuce drop
Identification tip: Older leaves wilt and eventually the entire plant wilts and collapses, making it unharvestable.

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.

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

Corky root
Corky root damage
Identification tip:  Roots show reduced feeder roots and a rough, pitted taproot.
Ammonium toxicity
Ammonium toxicity
Identification tip: Discolored vascular tissue caused by ammonium toxicity.
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.

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