Master Gardeners - Lettuce Problems

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LETTUCE PROBLEMS

Nancy Garrison, Horticulture Advisor

WHAT THE PROBLEM LOOKS LIKE PROBABLE CAUSE HOW TO DEAL WITH PROBLEM REMARKS

Curled or distorted leaves. Stunted plants. Aphids. Tiny green, pink or black soft- bodied insects that cluster on underside of leaves or roots. Through, forceful spraying of plants with water will reduce infestation. Apply malathion only for severe infestations, coverage of under surface of leaves is essential.

Leaves with ragged holes. Leaves devoured holes bored into heads of head lettuce. Cabbage looper. Pale green measuring worm (inchworm) with light stripes along back. Grows to 1 1/2 inches long. Alfalfa looper. Dark green with 3 dark stripes along back. Grows to 1 inch long. Hand-pick worms or apply Dipel or Carbaryl (Sevin). Alfalfa looper is common along the coast than inland.

Leaves skeletonized or almost totally destroyed. Loose webbing between leaves. Beet armyworm. Color of mature worms (1 to 1 1/2 inches long) ranges from bright green to purplish green. Most common color is light olive-green with dark dotted or lined stripe and two paler stripes lengthwise on back. Hand-pick or apply Carbaryl (Sevin).

Small holes in leaves, or leaves heavily skeletonized Vegetable weevil. Larvae (immatureweevils) are green, legless grubs 3/8 inch long when full grown. Adults are brown or gray snout beetles 3/8 inch long. Both larvae and adults move slowly and sluggishly. Because adults do not fly, infestation of new areas takes place slowly and damage is usually spotty. This insect also attacks other vegetables, including carrots, radish and turnip.

Inner leaves of head lettuce black and slimy on edges. Hot weather Do not plant lettuce for harvest in warmest months.

Speckles or mottled leaves of head lettuce. Stunted growth. Mosaic Virus Buy and plant virus-free seed if available. No practical control after symptoms on plants occur. Plants showing symptoms near harvest are edible. Plants which show symptoms early may produce no or only small heads.

WHAT THE PROBLEM LOOKS LIKE	PROBABLE CAUSE	HOW TO DEAL WITH PROBLEM	REMARKS
Curled or distorted leaves. Stunted plants.	Aphids. Tiny green, pink or black soft- bodied insects that cluster on underside of leaves or roots.	Through, forceful spraying of plants with water will reduce infestation. Apply malathion only for severe infestations, coverage of under surface of leaves is essential.
Leaves with ragged holes. Leaves devoured holes bored into heads of head lettuce.	Cabbage looper. Pale green measuring worm (inchworm) with light stripes along back. Grows to 1 1/2 inches long. Alfalfa looper. Dark green with 3 dark stripes along back. Grows to 1 inch long.	Hand-pick worms or apply Dipel or Carbaryl (Sevin).	Alfalfa looper is common along the coast than inland.
Leaves skeletonized or almost totally destroyed. Loose webbing between leaves.	Beet armyworm. Color of mature worms (1 to 1 1/2 inches long) ranges from bright green to purplish green. Most common color is light olive-green with dark dotted or lined stripe and two paler stripes lengthwise on back.	Hand-pick or apply Carbaryl (Sevin).
Small holes in leaves, or leaves heavily skeletonized	Vegetable weevil. Larvae (immatureweevils) are green, legless grubs 3/8 inch long when full grown. Adults are brown or gray snout beetles 3/8 inch long. Both larvae and adults move slowly and sluggishly.	Because adults do not fly, infestation of new areas takes place slowly and damage is usually spotty. This insect also attacks other vegetables, including carrots, radish and turnip.
Inner leaves of head lettuce black and slimy on edges.	Hot weather	Do not plant lettuce for harvest in warmest months.
Speckles or mottled leaves of head lettuce. Stunted growth.	Mosaic Virus	Buy and plant virus-free seed if available. No practical control after symptoms on plants occur.	Plants showing symptoms near harvest are edible. Plants which show symptoms early may produce no or only small heads.