Archived Story

Caterpillars are cleverly hidden [UPDATED]

Published 7:45am Monday, May 19, 2014 Updated 8:46am Monday, May 19, 2014

Did you find protein in your cabbages last summer?

There’s nothing is worse than finding little green worms floating in the water you just cooked your cabbage in unless it’s finding one hidden in the raw broccoli.

This happens because, early last spring, you were visited by that little white butterfly or, perhaps, a dusky brown moth.

Both are the culprits who lay eggs on all the Brassica family. This includes cabbages, broccoli and Brussels sprouts.

The little green worm is the offspring of the white butterfly.

You may also have diamondback moth larvae. These are pale green, too, but have a light brown head.

There is another eater, too. The cross-striped cabbage worm.

He is fatter and has a blue-gray back and yellow stripe on his side.

All of them eat holes in your plants and, even worse, leave their droppings in them.  Yuk.

If you like the cabbage family, but not the worm poop or the worms, you will need to take action now.

Start by finding and destroying any wild mustard, or shepherd’s purse weeds. They can harbor the caterpillars.

As soon as you put your plants in the ground, cover them with a floating row cover.

This may also be called a plant quilt. This is a very light weight white fabric that lets in sun and rain but excludes insects if properly applied. That is the trick here.

The cover can’t just be weighted down with rocks, staples, or other weights. The edges must be buried in the soil.

If you are reusing a row cover, do a careful check to be sure there are no tears or holes in the fabric.

It doesn’t take a very big hole for the pests to enter and feast unnoticed until harvest time.

Encourage the tiny wasps that parasitize all caterpillars by planting sweet alyssum or other small flowered ornamentals in the garden. Don’t forget the dill. It is a favorite of the lady bug larvae.

While these little red dragons don’t kill caterpillars, they do eat many small insects, especially aphids.

If a cover is not practical, head for the poison row in your favorite nursery.

You are looking for BTK. It stands for Bacillus thuringiensis var. kurtski.

Another kind is BTA that has the variety of bacteria, aizawi.

These are bacteria found in soil that kill all caterpillars by paralyzing their gut when they ingest it.

The trick with these sprays is that you need to spray the whole plant including the bottom leaves. It is only effective for 24 to 48 hours and must be reapplied after a rain.

Spinosad is another insect killer but it is not specific to caterpillars.

It will kill butterflies, bees, parasitic wasps and flower flies. It is likely to cause an aphid outbreak if applied more than once.

It lasts about a week before you need to reapply it.

In the fall, clean up all residues of the cabbage family as soon as you harvest them.

This will help reduce pest eggs, pupae or larvae that have been hiding in the crops.

This summer, enjoy worm- and poop-free cabbages. You don’t really need that extra fiber and protein now, do you?


Bev Johnson is a West Otter Tail County Extension Master Gardener.

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