Why Caterpillars Are Invading Your Vegetable Beds—And How To Stop Them

When you discover a caterpillar in your vegetable garden, you may consider it just as rude as the one Alice encounters in Wonderland. Rude, because they do what they want and eat what they want. While some caterpillars become beautiful butterflies or moths that are welcome pollinators, most of the ones you find in your vegetable patch are just going to cause problems and possibly ruin your crops.

Identifying Caterpillars in Your Vegetable Beds

Even if you don’t see a caterpillar, you’ll know they’ve found your vegetable beds by the feeding holes in leaves, webbed or rolled leaves, excrement, or eggs under leaves.

Here’s how to identify common caterpillars in Southern vegetable gardens:

• Armyworm: The larvae of a moth, the green-striped caterpillar, have a distinctive inverted “Y” on the head and feed on a wide variety of vegetables.
• Cabbage Looper: A 1 to 1.5-inch green caterpillar with white lines. They move like an inchworm and feed on brassica crops like cabbage, broccoli, and kale. When disturbed, cabbage loopers frequently rear up like a cobra.
• Diamondback Moth: Small brown caterpillars just 0.5 inches prior to pupation in loosely woven cocoons on the underside of brassica leaves. When handled, they often drop and hang from a silk thread or thrash about violently.
• Tobacco Budworm: If you live in an area where tobacco or cotton is a field crop, you may find this black, red, or green caterpillar (color depends on what they have eaten). About 1.5 inches long, they are harmful to peppers and tomatoes.
• Tomato Hornworms: The most common pest of tomato plants, these large, green caterpillars develop eight white, V-shaped marks on each side and boast a black projection or “horn” on the last abdominal segment. They damage tomato leaves and fruit.

Reasons for Caterpillar Presence

If you love butterflies and garden moths for their beauty and pollinating abilities, then you have to love caterpillars (even the ones called worms). They hatch from eggs laid by adult butterflies or moths and eat voraciously until they form cocoons and pupate into their adult forms. They are a normal part of the ecosystem that contribute by consuming plant material and breaking it down to release nutrients back into the soil.

Just as monarch caterpillars prefer milkweed, those you find in the garden prefer the leaves and fruit of specific plants. Many species have a small window of activity in the spring, summer, or fall and disappear until the next year.

Impact of Caterpillars on Vegetable Gardens

The most recognizable damage caused by caterpillars is holes in the leaves or fruit of the plant. While a few holes may only affect the look of the plant, feeding damage is more serious on young plants. Too much munching can easily kill the plant, and missing leaves usually mean less produce. If the caterpillar population is allowed to get out of control and mature, there will be more eggs laid and more caterpillars in the seasons to come.

Natural Predators and Control Methods

There are some natural predators that love a caterpillar as a snack. Parasitic wasps, flies, lacewings, spiders, and birds will feed on them. If the idea of inviting more insects into your garden doesn’t appeal to you, add some helpful plants to help with caterpillar control.

Nasturtiums, dill, and mustard are favorite egg-laying targets for moths, so plant them to draw them away from the vegetables you are trying to grow. Another tip is to plant strongly scented flowers like marigolds or herbs, such as lavender, sage, and rosemary, that seem to deter the adults from moving in and laying their eggs.

The simplest control method is a daily stroll through the garden with a bucket of soapy water. Pluck the caterpillars from your plants and drop them in the bucket. If you plan ahead, you can cover crops with insect barrier fabrics (fine netting) to keep moths from landing on crops and laying eggs.

Finally, use a spray of Neem oil or an organic insecticide that contains Bacillus thuringiensis, a bacterial disease that only affects caterpillars and is commonly referred to as Bt. Read product labels to be sure the product is safe to use on vegetables.

Preventive Measures and Garden Management

To help prevent your vegetables from being eaten by caterpillars, follow these tips:

• Control weed growth where many species lay their eggs.
• Plant deterrents like marigolds and strongly scented herbs to keep egg-laying insects away.
• Remove caterpillars when you see them by picking them off by hand or using an organic product to kill them. This will break the cycle in your garden.
• Introduce predatory insects like parasitic wasps that prey on caterpillars and welcome birds in the garden.
• Rotate crops, especially brassicas, each year and till the garden soil well to destroy eggs.