Holes in tomato leaves

Work from the damage and the droppings, because the culprit is often hidden: hornworms are well camouflaged, and slugs feed at night and hide by day. Whole leaves missing from the top of the plant down, with dark green or black droppings on the leaves and ground below, is a hornworm. Small round shot-holes, mostly under 1/8 inch, scattered across the leaf are flea beetles. Irregular holes with smooth edges and shiny slime trails are slugs. A tomato can tolerate some leaf loss — UC IPM advises treating hornworms only when foliage damage is extensive or they are feeding on fruit — so the question worth answering is whether the fruit is next.

1. Tomato hornwormManduca quinquemaculataMost likelyWhole leaves eaten, often down to bare midribs, starting at the top of the plant and working down, with dark green or black droppings on the leaves and soil beneath. The caterpillar grows up to 10 cm long and is bright green and well camouflaged, so look for the droppings first and search the stems directly above them.Full pest profile →
2. Colorado potato beetleLeptinotarsa decemlineataAlso commonLeaves chewed away, with yellow adults carrying ten black stripes, clusters of orange eggs under the leaves, or humped red to salmon larvae with two rows of dark spots along each side. Potato is its preferred host, but tomato is on its host list.Full pest profile →
3. Cabbage looperTrichoplusia niLess oftenLarge holes chewed in the leaf, usually away from the edge, and a smooth pale green caterpillar with white side stripes that arches its back into a loop as it walks. It grows to about 1½ inches, far smaller than a hornworm.Full pest profile →
4. Flea beetlesPhyllotreta, Epitrix & other AlticinaeLess oftenDozens of small round shot-holes, mostly under 1/8 inch, and shallow pits, worst on seedlings and young plants in spring, with tiny dark or metallic beetles that jump when the plant is touched. Damage is usually not serious once plants are past the seedling stage.Full pest profile →
5. SlugsDeroceras reticulatum and other speciesLess oftenIrregular holes with smooth edges, made at night or in damp, cloudy weather, with shiny slime trails on the leaves or soil nearby. Low growth and ripening fruit close to the ground are the most exposed.Full pest profile →
6. Corn earwormHelicoverpa zeaLess oftenThe tomato fruitworm is a fruit pest: young larvae enter green fruit at the stem end and leave a watery cavity full of cast skins and droppings. If the leaves are intact and the fruit is holed, this is the one to look up.Full pest profile →