Cabbage Worms

During the warmer months, the caterpillars like to emerge. You might see pretty small butterflies around your plants! Take note because they are laying eggs that will later become tiny caterpillars - what we like to call cabbage loopers. We provide all the details for how to detect and eradicate these pests that can often be a nuisance in organic gardens!

Identification & Lifecycle:

The imported cabbage worms are actually the larval stage of a butterfly or moth! And believe it or not, there are multiple varieties!

Many people use the names "cabbage worms" and "cabbage loopers" interchangeably. However, they are actually two distinct species.

The imported cabbage worm (Pieris rapae) is a white butterfly with a black spot at the top of each wing. They are most active during the day and lay small oblong eggs that are almost yellow in color. The eggs can be laid on either the underside or topside of leaves. The caterpillars are green with a light yellow stripe running down their sides.

The cabbage looper (Trichoplusia ni) is slightly larger than the cabbage worm. It is actually a greyish-brown moth that is nocturnal. The eggs are small and white and are usually laid only on the underside of the leaves, usually towards the base of the plant. The caterpillars are light green with a whitish line running down it. They don't have legs in the middle section of their body, so they move in an "inchworm" fashion.

The adult moth/butterfly of these species lay their eggs on their target plant and fly away. Once the egg hatches, a small caterpillar emerges. The caterpillar feeds on the host plant as it grows and matures. After weeks of feeding on the plant, the caterpillar will transition into a pupae inside of a chrysalis (similar to a cocoon). Finally, it will then emerge as a flying insect.

Crops Affected:

Regardless of the species, these caterpillars all damage similar crops. Their primary targets are plants in the cabbage (Brassica) family. This plant family includes many common food crops, including:

• Kale
• Broccoli
• Cabbage
• Cauliflower
• Radish
• Turnips

Detection & Damage:

It can be very hard to detect cabbage worms and loopers. Their eggs are very small and often placed in the cracks and crevices of the leaves. The caterpillars can be voracious feeders, eating ragged holes into the leaves of the host plant. Younger caterpillars will usually only eat one layer of the leaf surface while older caterpillars will eat holes clean through the leaf. The holes are usually ragged in appearance. The veins and midrib of the leaves are usually left intact and unaffected.

Young plants are the most vulnerable to their damage. Healthy mature plants can usually sustain a fair amount of feeding before they are negatively affected. Because of this, it's important to protect young plants whenever possible.

Prevention & Treatment 

Manual removal of eggs and caterpillars is the most effective means of control. Check cabbage family plants frequently for eggs and caterpillars. It's important to check both the top and underside of leaves, along with cracks and crevices where they can hide. Use a damp cloth to wipe the leaves to remove the eggs or squish them between your thumb and forefinger. Pick and remove the caterpillars and drop them into a cup of soapy water to kill them.

Thin fabric covers can offer additional effective protection for plants. Called, floating row covers are made of a thin mesh fabric (also known as "tulle") which allows air and light to pass through but prevents the adult insects from coming into direct contact with the plant leaves to lay eggs. You can use a hoop or cage to help hold the floating row cover in place and tuck it around your plant, ensuring there is no access to the plant foliage. Note: Be sure to check for eggs and caterpillars under the row cover every few days after you cover the plant in case any established pests are trapped under the cover!

Insecticidal control may be necessary occasionally for wide-spread control. Effective natural insecticides include Bt (a naturally occurring bacillus bacteria), neem oil (a plant-based pesticide) and spinosads (a naturally occurring soil bacteria). All of these natural insecticides are most effective against young caterpillars and should be applied often enough to disrupt the lifecycle of the hatching caterpillars. Always follow the label on the product to ensure proper usage.