How to Control Cabbage Worms

Last week I gave up on brussels sprouts for this year and chopped them all down.  The green cabbage worms won.  I had been diligently checking every leaf every day and squishing – ugh! -the worms, which are actually caterpillars, but I then missed two days and things got completely out of control. 

      The pretty cabbage white butterfly that flits around the garden is the real culprit. She lays her eggs under the leaves of plants in the cabbage family which includes brussels sprouts, cabbage, broccoli, kohlrabi, cauliflower and kale.  When the eggs hatch, tiny green caterpillars chew the leaves to pieces, so much so that they can destroy the plant entirely if they chew the growing point in the center of the plant.  The color of the caterpillar almost exactly matches the leaf color making them difficult to spot.

      I really want to grow cabbage family plants next year, so I began to research ways to control the cabbage white and her offspring organically. 

      First on the list is daily checking and squishing, which as I said, requires diligence.  Covering the plants with floating row covers is a second option.  Make a tunnel with stiff wire or PVC pipe pushed into the ground on both sides of the row or bed.  Use clothes pins or clamps to secure the floating cover onto the supports, making sure both ends of the tunnel are covered and that the material covers right down to the soil line.

      Third, try planting a polyculture, a mixture of plants, to confuse the pests and make it difficult for them to find the cabbage family plants.  There are plants that actually repel cabbage whites and include dill, onions, garlic, marigolds, thyme, oregano, lavender, hyssop, mint, rosemary and sage. The first four in the list are annual plants and probably the easiest to include in a vegetable garden. 

      Bt, Bacillus thuringiensis, is a naturally occurring soil bacteria that can be purchased and sprayed on plants.  It kills the larvae of caterpillars and moths when they consume it.  It is non-toxic for all other insects, mammals, birds and people.  Follow directions on the label.

      I’m not sure of the science behind this final tip but it looks like fun and can’t hurt so I am certainly going to try it next year.  Apparently, cabbage whites are territorial, so if they spot a white butterfly already in the garden, they will look elsewhere.  I found a page of printable templates of cabbage white butterflies on the internet along with instructions on how to make them and place them in the garden.  Search “cabbage white butterfly decoy” for instructions.

      The only satisfaction I got from chopping down the brussels sprouts was the thought of the caterpillars on them starving as the leaves wilted and that the next day the cabbage white butterfly would have no place in my garden to lay her eggs. 

      With the tips above, next year I’ll have brussels sprouts!

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