My broccoli plants were destroyed this year by a small green caterpillar, actually hundreds of small green caterpillars. How do I prevent this from happening in the future? SB

The culprit in your case is likely the cabbage looper. Looper is kind of an unusual name, but since the larvae of the cabbage looper only have “true” legs in the front and the rear, they move in a manner similar to an inchworm or move by making a loop…thus the name looper.

Cabbage loopers are fond or more than your broccoli though, they will also enjoy cabbage, collards, cauliflower, turnips, lettuce, spinach, celery, parsley, beets, potatoes, and tomatoes in the home garden.

Loopers primarily overwinter as pupae in the soil but can also overwinter in cocoons on a variety of host plants. Somewhere around mid-April, the adults emerge as moths and mate. The female moths can lay around 300 eggs. With 3-5 generations per season here in Oklahoma, you can see how it won’t take long for them to become a problem pretty quickly in your garden.

The newly laid eggs hatch in about 3 days and begin to feed. Feeding occurs for the next 4 weeks. These caterpillars feed on leaves and tend to leave them “skeletonized” meaning all the leaf matter between the veins is gone.

Bt (bacillus thuringiensis) is a good organic pesticide to help us deal with caterpillars in general and works well on cabbage loopers. There are two strategies you can engage in to help prevent damage from the cabbage looper to your crops.

First, you can preemptively spray your plants every 10 days or so with Bt so that if the loopers show up, you will beat them down early. The downside to this strategy is that you will probably be applying more insecticide than you need over the course of the growing season.

A better strategy would be to keep an eye on your plants. If you see skeletonized leaves, take a closer look and you will most likely see the looper caterpillar. Bt is quite effective, so if you spray them at the initial stages of an infestation, it will work within a day or so. Then you will just need to stay vigilant and repeat the spraying if and when you see additional looper activity.

One thing to be sure to do when using pesticides (even organics) is read the label. When you read the label you not only learn how to use the product correctly, you will learn about the pre-harvest interval. The pre-harvest interval is the minimum period of time between when you can use the product and then harvest your crop for consumption. Typically, we prefer organic pesticides since they tend to have a shorter pre-harvest interval. Knowing your pesticide is key to successful and healthy gardening.

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org.