How to Control Cabbageworm and Moths in your Organic Garden

Along with slugs, cabbage moths and cabbageworms can do extensive damage to cabbage plants, and other brassicas such as broccoli, cauliflower or kale. But there are some effective ways to control cabbageworm in your organic garden.

There are several varieties of cabbage worms, moths, and loopers, but control is the same for all. The worm, or larvae, feed on tender leaves. Look for holes in leaves, but be sure to also look underneath leaves for newly hatched larvae.

Preventing Cabbageworm and Cabbage Moth Damage

Adult cabbageworm butterflies, or cabbage moths begin laying their eggs in the spring. If you are seeing these moths, you can be sure that they are laying eggs.

Thoroughly examine your plants, and hand pick worms and crush any eggs found on the leaves. The eggs resemble small yellow or white bullets most commonly found on the underside of leaves.

A very effective control is to cover your cabbage and other brassica with floating row cover before cabbage moths appear in the early spring. (This is the same type of cover you can use for frost protection). Row cover will prevent the moths from laying their eggs on your plants. These plants do not require pollination to reproduce, so it is safe to leave the row cover on throughout the growing season. Do keep in mind that this practice may raise the temperature under the cover, and brassicas do prefer cool temperatures. On the plus side, that means you may be able to plant your cabbage a week or so earlier than normal.

Especially in northern climates, turning your soil over in the fall will expose the moth chrysalises to freezing weather. We practice no-dig gardening and do not ever turn our soil over, but if I had a severe problem with cabbageworms and moths, I would certainly consider employing this method of control.

Another practice that I have used with some success is to sprinkle my plants with cornmeal. The worms eat the cornmeal, causing them to bloat and die.

Interplanting your brassicas with other vegetables or flowers can also be quite effective in controlling insect damage. For example, if I plant radishes alone, they are damaged by cabbageworm. If, however, I interplant them with lettuce, they remain pest-free.

Organic Products that Control Cabbageworm and Cabbage Moth

It is best practice to start with preventive measures like row covers, or hand picking to control cabbage worm, cabbage loopers, and cabbage moth. Only then is it advised to move on to organic products.

Bacillus thuringiensis (Bt) is a naturally occurring bacterium that paralyzes the digestive system of leaf feeding caterpillars. The leaves should be sprayed in early morning or evening since sunlight will degrade Bt. In addition, results are not immediate; it may take a few days for starvation to occur.

Cautions: Bacillus thuringiensis does not harm adult butterflies but will kill their larvae (caterpillars).

Spinosad is another naturally occurring bacterium used to control cabbagemoth, and other insects, by causing paralysis.

Cautions: Spinosad is moderately toxic to earthworms, and highly toxic to bees when still wet. Spray when bees are not active.

Neem Oil is extracted from the seeds of the neem tree, found in India. It is most cost-effective to purchase concentrated neem oil, which must then be diluted and mixed before spraying onto plants. For cabbage moths, neem oil is best used preventatively as a repellant as it is not as effective as a killer.

Cautions: Neem oil is generally considered safe, but must be applied correctly, or can cause harm. Spray only in the evening when beneficial insects are not active since it can kill them if directly sprayed with neem oil. Otherwise, it will not harm beneficial insects. In addition, neem oil can burn your plants if sprayed while it’s sunny.

Lastly, neem oil must be mixed properly. Since it does not mix with water, an emulsifier like dish liquid, or other liquid soap must be used. Add 1 teaspoon of liquid soap to 1 gallon of water, and 1 tablespoon of concentrated neem oil.  Shake well before spraying.

Harvesting Insect Damaged Brassicas

There is no harm in eating plants that have been damaged by cabbageworm. But be sure to soak these vegetables in salt water. The worms will die and float to the top of the water. This works for slugs and snails as well.

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