Tomato hornworms on Plants

Diagnosis

Check the soil beneath your tomato plants for large droppings that are black or green. Droppings like these usually indicate that hornworms are present. The host recorded for this problem is tomato, so tomato plants are the place to begin your search. Once you find a hornworm, look at it before you remove it, because not every one needs the same response. A hornworm that carries parasitic wasp eggs has ceased feeding, and the advice is to leave it on the plant. The wasps can emerge from it, and they are described as beneficial. Hornworm pupae live in the soil, and adults develop from them. Natural enemies normally keep hornworm populations under control. Bacillus thuringiensis and spinosad are both listed as effective against smaller larvae, which makes the size of the hornworm worth noting. No other signs of damage are documented for this problem on this page, so the droppings are the one clue to rely on.

Treatments

The treatments follow the order of cultural, organic and then chemical. Handpicking and snipping are the first methods listed, and they use no products at all. You can remove hornworms by hand, either by picking them off or by snipping them with shears. Discing or rototilling after harvest destroys pupae in the soil and prevents adults from developing. Leave any hornworm that carries parasitic wasp eggs on the plant, because feeding has ceased and the beneficial wasps can emerge. Hornworms that carry wasp eggs are the one case where the advice is to take no action against the insect. Natural enemies normally keep populations under control. Those are the cultural methods listed for this problem. Bacillus thuringiensis is the organic option, and it is effective against smaller larvae. Spinosad is the chemical option, and it is also effective against smaller larvae. Each product entry names its active ingredient, which makes it easy to check against the label. The product label is the legal instruction, so follow it for the crop and the site you are treating. Read the label before you buy or apply either product, and use it only on the crop and site it names. This page gives no dose, rate or spray interval, and it does not say either product is safe for pets, children, pollinators or edible crops.

Prevention

Work the soil after harvest, because discing or rototilling destroys pupae in soil and prevents adults from developing. The soil step is timed for after harvest, when pupae in the soil can be destroyed. Leaving hornworms that carry parasitic wasp eggs on the plant lets the beneficial wasps emerge, and natural enemies normally keep populations under control. Natural enemies include parasitic wasps, whose eggs are carried by some hornworms. A hornworm population kept under control by natural enemies is the outcome the source describes. Tomato plants are the recorded host, so these conditions apply to the soil beneath them. Checking under tomato plants for large black or green droppings tells you when hornworms are present. Spacing, watering and fertilizer choices are not documented as hornworm controls here.

Plants most often affected

Tomato is the host recorded for this problem. Large black or green droppings on the ground beneath tomato plants usually indicate hornworms. The treatments below are recorded for hornworms, including handpicking, soil work after harvest, and products for smaller larvae. Natural enemies normally keep hornworm populations under control.

• Garden Tomato