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Cabbage Worm Calendar

Several caterpillars feed on cabbage-family crops. A weekly check from transplanting to harvest catches them while they are small.

Which caterpillars are called cabbage worms?

The term covers several species that feed on brassicas such as cabbage, broccoli, kale, collards and cauliflower. The imported cabbageworm is a velvety green caterpillar that comes from a white butterfly. The cabbage looper moves in a looping way. The diamondback moth larva is small, wriggles when touched and feeds on leaf undersides.

Each species has a slightly different timing and damage pattern, so learn to identify them with extension photographs. Alabama Extension's crucifer scouting guidance describes scouting methods that apply across species. Learning the three species on sight saves time, because a quick look at the caterpillar tells you where on the plant to search and how fast the problem may grow.

When do cabbage worm problems begin?

Adults, which are butterflies or moths, arrive once brassicas are growing and the weather is mild. Female butterflies lay eggs on leaves, and the larvae hatch and start feeding in a few days in warm weather. The first sign is often a few white butterflies fluttering over the crop.

Spring plantings may face their first flight soon after transplanting. Fall plantings often face heavy pressure in the first weeks, because summer populations are large. In many regions, populations also decline in the heat of midsummer.

For example, if you set out fall broccoli during a warm spell and see white butterflies the same week, expect eggs within days and start leaf checks immediately instead of waiting a week.

How do you scout cabbage worms?

Check a set number of plants in several locations once a week, starting at transplant. Look at the undersides of outer leaves and into the center of each plant. For heading crops, check the wrapper leaves and the head itself near maturity. Count eggs, small larvae and large larvae.

Frass is a useful clue. Fresh green droppings show larvae are present. Alabama Extension's guidance and many other state guides recommend a regular sampling pattern and written records.

Record the percent of plants with eggs or larvae and the largest larval size seen. Those two numbers show whether damage is about to rise.

• Start at transplanting, then weekly
• Check undersides and plant centers
• Count eggs and larvae by size
• Watch for frass and ragged holes

How do thresholds depend on crop stage?

Young plants can be set back by feeding, while plants close to heading may need protection of the head itself. Extension thresholds often vary with crop stage, expressed as a percentage of plants infested. Use the version for your state.

For example, a grower selling heads for fresh market has less tolerance than one selling for processing, and a grower of kale leaves has a lower tolerance for any leaf damage. Heading crops can often tolerate feeding on outer wrapper leaves, so check what your buyers will accept before you set a limit.

What natural controls help?

Parasitic wasps attack cabbageworm larvae and pupae and are active in many fields. Predators such as lady beetles, lacewings and ground beetles feed on eggs and small larvae. Some caterpillars die of naturally occurring diseases in humid weather.

Protecting these allies means avoiding broad spectrum treatments where you can and following local guidance.

A field edge near flowering brassica weeds or last season's remaining plants often shows the earliest activity, so check there first.

What cultural steps reduce damage?

Floating row covers placed at transplanting and sealed at the edges keep butterflies and moths from laying eggs. Remove crop residue after harvest, since leftover plants allow populations to carry over. Rotate brassicas, and manage wild mustards and other brassica weeds that feed larvae.

Hand picking works in small plantings and is especially effective when larvae are still on outer leaves.

Cover only plants that will not need insect pollination, which includes most leafy brassicas grown for foliage or heads.

What about treatment and labels?

Biological and conventional products exist for caterpillars, and each has a label that sets crop, timing, pre-harvest interval and pollinator precautions. The label is the law. Resistance has been documented in diamondback moth, so rely on current local recommendations. Applicator licensing varies by state.

Your county extension office can recommend what fits your market and your certification, if you grow organically. Rotate which products and methods you use over the seasons, since repeated use of one approach speeds the loss of its effectiveness.

Last reviewed: November 2026. Educational information, ranges only. Confirm timing with your county extension office.

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