Lettuce
Symptom Cause  
Leaves wrinkled or curled; discolored, stunted, tend to fall off
Aphids
>
Leaves, stems and buds eaten
Armyworms
>
Young seedling pulled and partly eaten
Birds
>
Greenish or water-soaked spots on leaves; sunken lesions possible on stalks;
Blight, Early
>
Greenish or water-soaked spots on leaves; sunken lesions possible on stalks;
Blight, Late
>
Rust-colored spots on leaves
Bottom Rot
>
Holes in leaves
Cabbage Loopers
>
Seedling stems severed
Cutworms
>
Seedlings rot and die
Damping-Off
>
Plant chewed to soil
Deer
>
White powder on leaf bottoms, leaves wilt
Downy Mildew
>
Tiny, black hopping insect, shot holes in foliage
Flea Beetles
>
Plants “bolt”; go to seed
Hot Weather
>
Tip of leaves brown, internal larvae trails visible.
Leaf Miners
>
Leaves curl, yellow or brown, brittle
Leafhoppers
>
Leaves mottled yellow and green, raised dark areas; plant stunted
Mosaic Viruses
>
Plants stunted, yellow
Nematodes
>
Roots eaten, plant may disappear
Pocket Gophers
>
Leaves coated with white powder
Powdery Mildew
>
Seedlings are chewed or eaten entirely
Rabbits
>
Plant chewed to soil
Rabbits
>
Large ragged holes in leaves, often in middle
Slugs
>
Large ragged holes in leaves
Slugs
>
Weakened plant, leaves yellowed, appears like flying dandruff when foliage disturbed
Whiteflies
>
Plant chewed to soil
Woodchucks
>