How I control Asparagus Beetles

Every year I get visited by Spotted Asparagus Beetles (Crioceris duodecimpunctata). These guys mate, lay eggs and the grubs that emerge eat my asparagus bare.

Poor photo of spotted beetle, and of the bare ends of my asparagus plants.

Spotted asparagus beetle grubs on my asparagus. They can clear a branch in a day. They are hard to pick up and squish easily.

They attract lady bugs and these help to control them.

Big Breakthrough this year in controlling the Asparagus Beetles

I rotate my planting in the garden. This helps keep pests down. Last year I had the parsnips near the asparagus plants. No noticeable effect. This year, I noticed that one of the parsnips had not been dug up and was starting to flower. I left it there thinking I would collect and try the seeds next season.

Parsnips are biannual which means they flower on their second year. They are notoriously poor germinators. I hoped that fresh seeds would work better.

There are oodles of bugs that make a living in my garden. The newly opened parsnip flowers attracted the usual pollinators, hoverflies, bees and wasps.

One day I walked by and noticed it was covered with large iridescent black and blue wasps with tiny waists. I'd seen them before on queen anne's lace flowers. Adult wasps eat pollen so they are regular visitors.

These Thread waisted wasps are common in my garden and they make mud tunnels on my porch.

Although the adults prefer pollen, the wasp larva live on insect grubs. The mother goes and finds a nice grub, carries it away and lays an egg on it. The wasp larva gradually eats the grub. I knew that they helped control the asparagus beetle larva because in previous years I had watched wasps carry off the asparagus beetle grubs but now that they were congregating and feeding just a couple of feet away, all they had to do was have a good meal then hop over to the asparagus and catch a grub.

I noticed that although I could see adult Spotted Asparagus Beetles on the plants having a merry old time, so I knew they were around, but I could not see any grubs, and, my asparagus was not eaten.

Chance had made me plant the parsnip near the asparagus, and allowed one plant to survive and flower. I was lucky to reap the benefit.

Companion Planting at its Best

Here is a perfect example of companion planting at it's best. One plant provides food for a pollinating wasp with pollen. The wasp then goes and removes grubs from the asparagus plant to feed it's babies. The wasp is happy because both it's babies and itself are fed, the parsnip is happy because it's being pollinated, the asparagus is happy because he's not getting eaten and from my point of view, I'M HAPPY because my asparagus is thriving and I get asparagus, and parsnip seeds.

Although gardeners speak of companion planting, scientists speak of INTERCROPPING.

Intercropping can work in many ways. I had another great example of another mechanism of plant protection at work in my garden. Read about how the turnips I planted near the swiss chard attracted all the slugs and snails and kept the swiss chard and beets clear of holes. Plus I got turnips! All I had to do was collect the concentrated slugs and snails from the turnip leaves.

Since these wasps also like queen anne's lace planting a few around your asparagus patch might work just as well. They have the benefit of also attracting black swallowtail butterflies whose caterpillars like to eat the leaves.

In order to get a parsnip flower you either need to plant a parsnip and wait a year, OR you can go to the supermarket, find a nice healthy parsnip root and plant this. I think planting a root in late summer or early fall would work best. If it did not come up in the spring, then planting again with another parsnip root might work just as well.

I've had good luck with parsnip. They take a while to germinate and you have to expect only about half will come up so plant more than you need an thin later. An important thing to consider is to plant a heirloom plant so it can flower and produce seeds. No flowers, no wasps.

You also need to take care of the wasps!

For this to work you also need to take care of the wasps. Since they are not particularly aggressive they don't usually bite. What they do though, is make little mud houses. If you want wasps to come and eat your grubs you have to let them build their houses. They don't make huge nests like the yellow jackets and I've never had any of these guys chase me or bite.

Here is another bunch of wasps feeding on dill flowers. This lot spends their time patrolling the garden. I'm not sure what they are looking for but I have seen a grand total of 5 cabbage worms this year so someone is taking care of them. I suspect these wasps are doing the job helped by the birds. That's why I allow a few dill plants to grow here and there in the garden for them.

What I learned from this lucky break: WASPS ARE MY FRIENDS

From now on I will have parsnip and queen anne's lace around the asparagus to make sure the wasps are attracted to the area. I will also keep planting dill to look after the other wasps. I'm lucky, I have a large area I've planted with flowers and all summer long it is a buzz with insects that help pollinate and keep my vegetables clean.

Small Print

This information is for general knowledge. I don't claim to be an expert on anything. The information on this page comes from personal experience.

email: Christine