Look for cabbageworms now
Noticeable numbers of imported cabbageworms are starting to show up in southeastern Michigan vegetable gardens.
It’s safe today these pests are public enemy No. 1 when it comes to growing cabbage and related crops including: broccoli, cauliflower, kale, kohlrabi, turnips, rutabaga, chard, mustard and more that I can’t think of right now.
Imported cabbage worms will sometimes feed on other greens too. I’ve even found them on lettuce in the past.
Because the worms are so well camouflaged, beginning gardeners have a hard time spotting them. Their coloring is nearly the same hue as a cabbage leaf and they like to rest along the leaf veins making them even more invisible. Experienced gardeners can sometimes have a hard time finding them too but recognize all too well the damage they cause.
The first signs are small holes in the outer part of the leaves where the caterpillar started its life. Are they put on some weight and bulk, they move to the center of the plant where active plant growth is happening. They grow fast and eat a lot, as a result they also poop a lot. It is their abundant frass voided by the worms that gardeners often notice first.
The imported cabbage worm is a caterpillar so it goes through the same lifecycle as other caterpillars existing as an egg, pupa (chrysalis) and adult butterfly. They can go through their lifecycle two or three times a summer producing a new generation of worms with each cycle.
The adults are those small, white butterflies that can be seen fluttering around any garden that has susceptible plants growing in it. It’s not unusual to see dozens of butterflies in a cabbage patch later in the summer.
A fun game for kids is following a female butterfly and watching where she lands. Every time she briefly touches a leaf, she lays a very tiny, white, elongated egg that soon turns yellow.
After about a week a tiny caterpillar hatches from the egg and starts feeding immediately.
Hand picking the worms from leaves is an effective control if there are only a few plants to deal with. You can develop a pretty good eye for them once you start picking.
The microbial insecticide Bt. is a safe and effective material to control imported cabbage worms and other caterpillars without harming beneficial insect species. Many of those beneficial species are part of the checks and balances that help to lower the caterpillar population.
Avoid using artificial broad-spectrum insecticides, they will readily kill caterpillars but will also take out the good guys at the same time.
You can make a DIY bio-insecticide consisting of a naturally occurring virus extracted from sick caterpillars. Start by collecting sick-looking caterpillars. Drop the worms into a container of water and let them soak to release viruses. Spray the virus solution over worm-infested cabbage. As the caterpillars feed, they will ingest the virus, become infected and eventually die.
Your homemade insecticide will kill caterpillars but will be completely harmless to other insects, birds or mammals.
Whichever insecticide you decide to use, apply it early when the worms are small. The smaller they are, the more effective the insecticide will be.