Insects Affecting Tomato Leaves

Caterpillars

• Several species of caterpillar feed on the leaves of tomato plants. The tomato hornworm -- distinguished by the curved "horn" projecting from its posterior and eight diagonal stripes on its back -- can badly defoliate plants, as can the beet armyworm. Since these caterpillars are large, you can handpick them from plants or use a biological or conventional insecticide.

  Despite its name, the tomato fruitworm also feeds on foliage and may burrow into the leaf midrib. They feed on leaves inside the buds and cause distorted growth.

Aphids

• Aphids extract sap from the leaves of plants with their slender mouthparts. Greenish in color and tiny in size, they occur in large multitudes, and their feeding activity can cause leaves to curl and distort. They also spread diseases that can kill plants. Plants shed blossoms, then turn brown and die from the top down. Low-toxic insecticides like insecticidal soap will kill aphids.

Whiteflies

• Whiteflies primarily affect greenhouse tomatoes. Like aphids, these tiny bugs suck sap from foliage and spread diseases to tomatoes. Leaves may develop yellow spots, then begin to wilt. Whiteflies also excrete honeydew, which can cause a secondary sooty mold infection to develop on the leaves and further reduce plant vigor.

Psyllids

• Psyllids can cause severe damage to tomatoes. The tiny insects suck sap from the leaves, simultaneously injecting a chemical that arrests growth of the leaves, which twist and discolor. Young psyllids are green and resemble aphids, while adults are black-and-white striped and jump when disturbed. Treating psyllids is essential to protect plant health and should incorporate sulfur dust, insecticidal soap or an approved insecticide.

Flea Beetles

• Minute flea beetles hop away readily when disturbed, earning their name. These tiny foliage feeders leave small holes in the leaves of tomato plants that give the leaves a lace-like appearance. Flea beetles pose the greatest risk to seedling plants that cannot withstand the hundreds of tiny nibbles inflicted on them by this pest. Mature plants can usually withstand infestations. Since insecticides aren't effective on this pest, trap-crop during the seedling stage by planting radishes near your tomato seedlings or use a repellent like diatomaceous earth, horticultural oils or neem oil.

Leaf Miner

• Leaf miners burrow between the layers of leaf tissue, leaving a squiggly trail of yellow tissue visible on the leaf surface. Leaf miners can cause stunted growth and reduced yield in tomatoes. Yellow sticky traps can attract and capture leaf miners before they damage your plants.