Home & Garden

Caterpillars make a mess of your tomatoes

Let me begin by asking you all to NOT send me specimens in the mail. At least, not in a regular envelope.

The sorting system used by the U.S. Postal Service runs these envelopes through rollers that crush anything in them. Couple that with the fact that I go to the Sun Herald only on Fridays to pick up my mail, and you can see the problem.

Last Friday, an envelope was waiting for me that contained a plastic bag (thank goodness) that contained the rotting remains of what had once been two caterpillars. If it hadn’t been for the fairly good description of the damage they’d done, I would have been at a complete loss as to what they were. As it was, I narrowed the culprits down to two species, first cousins in the family Noctuidae.

The gentleman who sent the crushed caterpillars was having a problem with them consuming his Better Boy tomatoes and was asking what he could do about them.

Fortunately, since they were first cousins, what would work for one would work for the other.

The species in question were the tobacco bud worm (Heliothis virescens) and the tomato fruit worm (Helecoverpa zea). Both of these are major pests of row crops such as tobacco, cotton and corn and have been studied extensively.

I spent 12 years studying H. virescens in cotton in the Mississippi Delta, where they were the No.1 problem.

The eggs of these pests are fairly unnoticeable, measuring about the size of the period at the end of this sentence.

Depending on temperature, the young hatch in from two to 10 days. When fully grown, the caterpillars range from black, brown and green pink to yellow with tan heads. The color often is determined by what they ate.

The young caterpillars begin their feeding at the base of the stem of the tomato. Once you’ve harvested your tomato, you will see tunneling, and the interior may contain rotted areas along with frass (caterpillar poo). When they’ve finished eating, they gnaw their way out and burrow into the soil, where they form a pupal case, emerging in less than two weeks to start the whole cycle over again. Here in South Mississippi, the entire cycle can take as little as four weeks, with up to five generations a year.

To control these pests, you have to begin by collecting and disposing any infested berries (yes, tomatoes are fruit, not veggies). One of the best control methods is to introduce a bacterium called Bt. This is a biological control that kills only caterpillars. The benefit of Bt is that, once consumed, the caterpillars stop eating, causing no more damage. Bt, commonly sold under the name Dipel, has to be applied often. Irrigation or a good rain will wash it away.

Your second option is applying pesticides. Most of the synthetic pyrethroids work well.

Find an insecticide labeled for garden use that contains bifinthrin, beta (or lambda) cyhalothrin, cyfluthrin or pyrethrin. These have good residual activity and fruit can be picked and eaten, for the most part, in 24 to 48 hours after application. Traditional pesticides such as Sevin dust are more problematic and need 25 or 50 times the percent of active ingredient and require that you not eat the tomatoes for two weeks after treatment.

If you have a big enough infestation in your garden (check your bell peppers and corn as well), you may find these same pests infesting your flowers. They have a particular taste for ageratum, geraniums, marigolds, nicotiana, petunias, snapdragons and zinnias — just to name a few.

Be vigilant and, please, if you have to send me specimens, put them in a small box. You wouldn’t believe the smell of a smushed bug after a week in the mail.

Tim Lockley, a specialist in entomology, is retired from a 30-year career as a research scientist for the U.S. Department of Agriculture. For answers to individual questions, please send a stamped, self-addressed envelope to Tim Lockley, c/o Sun Herald, P.O. Box 4567, Biloxi MS 39535.