Parsley Worm Caterpillars

Daniel Gill  |  8/8/2015 3:10:26 AM

Dan,

I have a problem. I love parsley and use it a lot in cooking - so I grow a lot as well. Over the past two years I have been plagued with these pale yellow caterpillars with stripes and orange horns. They can eat all the parsley in a pot overnight. I don’t know where they come from. I had the pots on a fence with pot clips. Most recently, I had them in hanging baskets hanging from my shed far away from anything and covered with netting - and then they suddenly appeared again yesterday.

First off, where do they come from? Secondly, how do I protect my parsley from these pests?

I’ve met you a couple of times at shows, read your weekly column, and really appreciate what you do for the community. Thanks for any guidance you can give.

- Dave C.

These are called parsley worms. They are the larvae of the black swallowtail butterfly, one of our lovely native butterflies. Butterfly gardeners plant parsley (as well as dill and fennel) in butterfly gardens in hopes that female black swallowtail butterflies will lay their eggs on the plants increasing the population of the butterflies. People tend to have a soft spot when it comes to butterflies.

The female butterfly can fly, of course, and this allows her to lay eggs anywhere she can find parsley plants, even in pots and hanging baskets. If you had a plant covered with netting, either the eggs were laid before you covered the plant or the female butterfly somehow managed to get under the netting or laid her eggs on leaves by sticking her abdomen through the netting.

When the caterpillars compete with you for your parsley and cause more damage than is acceptable, you may choose to kill them – even though they do grow up to be butterflies. But, you need to do it at an earlier stage instead of waiting for them to eat, grow large and cause so much damage.

When the parsley worm caterpillars hatch from the egg they are tiny. They eat and gradually grow bigger over time. When they are small, the damage is not as noticeable. Once they get large, they can cause a lot of damage quickly. But, it takes a while for that to happen. If you will observe your plant frequently and carefully for early signs of feeding and small caterpillars, you can pick them off and destroy them before they cause so much damage.

The other option is to spray the plants constantly with an insecticide to kill any caterpillars that show up to feed on your parsley. I’d recommend an organic biological insecticide with Bt, such as Dipel, Thuricide and other brands. Spray your parsley plants about once a week to keep them protected.

Dan Gill
Consumer Horticulture Specialist

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