US: Ugly caterpillar causes havoc among tomatoes

When it comes to ugly, few garden pests rival the tomato hornworm. They look like something out of a 1950s Japanese horror flick: a fat, green caterpillar with bulging eyes and a red spike on its head -- hence, the name. Hornworms, aphids, fruitworms and blossom-end rot are formidable opponents this time of year. Unlike Rodan and Godzilla, they needn't get the upper hand.

Tomato hornworms reach 3 to 5 inches when mature, fueled by tomato leaves. They seemingly arrive overnight and strip plants bare in two days. Beneath bare stems, you'll see piles of dark, uniformly shaped droppings.

Deer and rabbits sometimes get the blame because we are unable to see what's really going on. If you find piles of droppings on lower leaves, check the undersides of denuded branches. There you will likely see the hornworm clinging to the underside of the stem. They're tough to see because hornworms -- the larvae of a largish brown moth, are the same color as the plant leaves.

"With this perfect camouflage coloration, tomato hornworms may go unnoticed until they reach nearly their full size -- 3 to 4 inches," said Walter Pett, a Michigan State University entomologist. "At this point, they can defoliate whole plants virtually overnight. Suddenly, leafless stems and fecal pellets on the plant and on the ground beneath it tell you tomato hornworms have been at work."

The best method of control is to simply pick them off. They hold on tightly, so give 'em a good yank. They'll curl up to let you know of their discontent. Keep checking to make sure new recruits haven't arrived.

A non-chemical alternative is to spray plants with Bacillus thuringiensis kurstaki, a bacterial disease of caterpillars formulated as an insecticide. Thoroughly cover the plant and reapply after a rain or overhead watering. It works best on smaller caterpillars, so don't wait until you see extensive damage, Pett said.

Other tomato pests include the tomato fruitworm, which are like finicky kids at a buffet. They move from tomato to tomato and damage several without eating the equivalent of a single fruit.

Tomato fruitworm moths arrive in Michigan from the south about mid-August and lay their eggs on the undersides of tomato leaves. As soon as the egg hatches, the caterpillar finds a tomato and bores in unless it comes into contact with an insecticide while it's moving.

"These are the same insect that we call corn earworm when it's in sweet corn and cotton bollworm in cotton," Pett said. "They're rarely a significant problem in tomatoes in Michigan."

Higher on the scale of problematic insects, and not just for tomatoes, are aphids. These small, soft-bodied insects suck plant sap and multiply quickly when the weather is hot, so it's been a banner year.

Tomatoes can handle high infestations, though aphid feeding can stunt plants. Use a forceful spray from the garden hose or insecticidal soap to control aphids without pesticides.

You don't need the hose or pesticides to battle a common problem of tomatoes called blossom-end rot. Tomato, cucumbers, pumpkins and peppers are susceptible. It is marked by dark sunken areas at the bottom of fruits.

This one is rooted in soil conditions and watering habits. Large amounts of water followed by prolonged dry spells cause blossom-end rot. It is best not to let the soil dry out completely before tomatoes are watered again. Mulch spread around the root zone -- but not packed against the stem -- can help.

Calcium deficiency is another cause, but can be remedied easily by adding bone meal to the soil. Another organic approach, from garden expert and author Jerry Baker, is called eggshell tea. Crush egg shells into little pieces and put them into a gallon milk container filled nearly to the top with water. When the brew starts to smell like rotten eggs, dilute it with an equal amount of water and pour at the base of tomato plants.

The aroma might ward off other pests, from neighbors or hornworms. Remember, hornworms have a single red spike on their head, not two.

Source: mlive.com

Publication date: 8/14/2007

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