From Butterflies to Brassicas: Identifying and Controlling the Imported Cabbage Worm - Megen Toaldo, Sales Associate  

Have you ever noticed small white butterflies circling through your garden?  After you have admired their graceful garden dance, check the undersides of the leaves of your brassica plants, such as cabbage, broccoli, kale, collards, and brussels sprouts.  You are likely to find this garden pest in its larval form, commonly referred to as the cabbage worm.  They are small, green, velvety, and have a resemblance to inchworms. 

It is possible that you may have already noticed the damage to your plants.  The Cabbage worms, the larval form of the Cabbage White Butterfly, build their chrysalis in the fall and hatch as butterflies in the spring.  The butterfly feeds on nectar and then lays single eggs on the undersides of brassica leaves.  The eggs hatch in about one week and the larva feed ravenously on the leaves of the host plant leaving it full of holes and dark green droppings that are easy to see as you wander through your garden. You may also keep your eye out for entry holes on the heads of cabbages where the worms will burrow their way in for a heavier meal. 

This common pest can be a nuisance, but can usually be identified early enough to control before the problem gets out of hand.  Check your plants frequently for worms, especially if you spot the butterfly fluttering about.  You can also use floating row cover as a preventative measure in the spring and early summer when egg laying activity is high.  Some folks recommend slipping a nylon stocking over the heads of your cabbage plants to prevent the worms from burrowing in.

While a serious infestation can lead to the death of the host plant, minor infestations can be easily controlled by picking off the worms and destroying them.  If the infestation becomes more than you can handle, Dipel, a biological insecticide containing the bacteria Bacillis thuringiensis (bt), is approved for organic use and can be sprayed on your plants (being sure to cover the undersides of the leaves as well). Once the worms ingest a lethal dose, they will stop feeding within the hour and die within 3 days.  For the best effect, alternate the use of Dipel with Entrust, which is spinosad (a fermented byproduct of a soil dwelling bacterium Saccharpolyspora spinosa.  With Entrust, the worms cease feeding and become paralyzed just moments after ingestion.  Alternating use of these two biological controls will help to limit tolerance to one or the other.

Now that you are in the know, you can enjoy helping your garden grow!