Bore holes in tomatoes

Asked August 5, 2016, 1:26 PM EDT

My tomatoes are starting to get round, bore holes in them. I have not yet found any insect associated with the holes, but I'm sure it has to be one. What can I do to save my tomatoes? I have Captain Jack, a spinosad, that I use for other pests.

Multnomah County Oregon

1 Response

You have helicoverpa zea. I give you the scientific name since it is also known at the tomato fruitworm, corn earworm and cotton bollworm. It attacks all those plants as well as peppers.

It is a moth that is light-yellow olive in color that lays its small eggs on the leaves of the tomato.The newly hatched caterpillar will eat its egg shell and then feed on tender leaves. Older caterpillars feed on older leaves and tunnel into tomatoes. Caterpillars have silk glands and produce silk threads around feeding sites. They also leave excrement in and underneath feeding sites.

The caterpillars bore into the tomato fruit and then out again when they are ready to pupate. The caterpillars eat for 2-3 weeks. The caterpillar crawls down to the ground, and pupates, making a hard brown shell around itself and then emerges as an adult moth in 2 weeks during the summer. The pupaes can overwinter and the cycle from egg to moth can repeat two or three times during the summer.

If you have a lot of holes, you had a lot of caterpillars but they are gone now, pupating in the ground and turning into moths. (I have had holes in my tomatoes and peppers caused by these caterpillars, but like you, I’ve never actually see the caterpillars.)

I can’t find any recommendation to till around the plants to destroy the pupae, so that doesn’t work, There are lures for the adult moths, but I don't know how well they work.

The best you can do is try to stop the next generation. You will want to watch for tiny eggs and tiny caterpillars. A magnifying glass is useful. Searching an entire tomato plant is fairly daunting, but extensive research had been done on this pest since can they destroy a commercial farmer’s tomato crop with the holes in the fruit. Researchers have determined the best place to look for eggs is on the first branch of leaves just below the top-most flowers on the plant. I’ve included pictures of where to look and what the eggs look like.

if you don't want to use insecticides, caterpillars can be picked from plants or collected using a sweep net or drop cloth.

Spinosad, the active ingredient in Captain Jack, is not one of the recommended insecticides for control of tomato fruitworm. This reference includes general information about this pest as well as recommended insecticides. Brand names are not included, so you will have to read the label.

The least toxic insecticides are the ones noted as organic. Bacillus thuringiensis var. kurstaki (Btk) is very effective against caterpillars and generally easy to find, but I suggest not spraying until you see eggs or caterpillars.

If you have any further questions, don’t hesitate to e-mail again.