Tomato Plants Targeted by Insects and Disease

Protect Garden Favorite From Hornworms, Aphids and Blossom-End Rot

Aug 4, 2009

The satisfaction that comes from harvesting home-grown tomatoes can be tempered by fruit-marring diseases and the destruction of plant leaves by tomato hornworms.

This formidable garden pest is difficult to spot when young, but in a matter of days can strip plants bare of leaves. By this point, hornworms are easier to see, having developed into fat, green caterpillars up to five inches long with bulging eyes and a red spike on its head.

Tomato Tormentors

Hornworms, the larvae of a large brown moth, are the same color as plant leaves and difficult to spot. Look for piles of dark droppings on lower leaves and inspect the undersides of denuded stems.

“With this perfect camouflage coloration, tomato hornworms may go unnoticed until they reach nearly full size,’’ Michigan State University entomologist Walter Pett said in a news release. “At this point, they can defoliate whole plants virtually overnight.’’

Getting Control

The best method of control is to simply pick them off. They hold on tightly, but gentle pressure while pulling at it will cause the hornworm to lose its grip. Inspect each plant daily to ensure new recruits haven’t moved in.

For people squeamish about handling the large caterpillar, hornworms can be controlled with Bacillus thuringiensis kurstaki, a bacterial disease of caterpillars formulated as an insecticide. Thoroughly cover the plant and reapply after overhead watering. It works best on small caterpillars, so don’t wait until you see extensive damage, Pett said.

Other Tomato Foes

Tomatoes may also be bothered by the tomato fruitworm, which moves from tomato to tomato, damaging each with selective feeding.

They typically begin to show up in mid-August and lay eggs on the undersides of tomato leaves. As soon as the egg hatches, the caterpillar finds a tomato and bores in unless it comes in contact with an insecticide while it is moving.

“These are the same insect that we call corn earworm when it’s in sweet corn and cotton bollworm in cotton,’’ Pett said.

Aphids are another plant-damaging insect that feeds on juices and multiplies quickly in hot weather. Tomato plants will tolerate some infestation from soft-bodied aphids, though prolonged feeding can stunt plants. Use a forceful spray from the garden hose or insecticidal soap to control aphids without pesticides, Pett said.

Blossom End Rot Ruins Fruits

A common disease of tomatoes, cucumbers, pumpkins and peppers is blossom-end rot, which appears as dark sunken areas at the bottom of fruits. Blossom-end rot 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, will help conserve moisture and keep soil-borne diseases from splashing onto foliage and fruits.

Micronutrients Help Plants Thrive

Calcium deficiency is another cause for blossom-end rot, but can be remedied by adding bone meal to the soil. Organic gardeners also advocate mixing pulverized egg shells with water and pouring at the base of plants.

Some liquid organic fertilizers, such as fish emulsion, contain micronutrients to keep plants and fruits healthy, John Venman, owner of Venman's Landscape and Soil-Alive Fertilizers in Rockford, MI, said in an interview.

"If you can tolerate the temporary odor, fish emulsion is a good all-around organic fertilizer for plants,' Venman said. "It is also good for the soil and healthy soil is the key to gardening sucess.'

The copyright of the article Tomato Plants Targeted by Insects and Disease in Garden Pests & Diseases is owned by John Hogan. Permission to republish Tomato Plants Targeted by Insects and Disease in print or online must be granted by the author in writing.