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