How to Identify, Control, and Prevent Asparagus Beetles

Asparagus is a great crop to grow. This perennial produces delicious spears every year in the spring. But there is a downside to growing this phenomenal edible: the asparagus beetle.

You might not be alarmed when you see the first beetles. But if they’re not dealt with quickly, your problem will multiply. It’s important not to let these beetles get out of hand in the garden, particularly if you want to save your crops.

I’ll tell you everything you need to know about asparagus beetles and how to get rid of them.

What Are Asparagus Beetles?

While technically there are four known types of Crioceris, only two have been recorded in modern times.

If you see an odd-colored beetle that’s a bluish-black in color with red and white, it might be the common asparagus beetle, Crioceris asparagi.

The common asparagus beetle is mostly blue-black, but has cream-colored or pale yellow spots along its back, and an orangish or reddish border to its wings. It has an elongated head with feathery-looking antennae. This is by far the most common asparagus beetle and the one the most devastating around asparagus plants.

The spotted asparagus beetle is often mistaken as a weird ladybug, but this is no beneficial insect.

Often seen as a pumpkin-colored orange beetle with black spots in the western United States, or a medium to dark red beetle with black spots in the east, it is similar in some regards to a ladybug. That is, until you look at its elongated head and almost feathery-looking antennae.

The spotted asparagus beetle is not as destructive to asparagus, but still feeds on it, as I’ll explain a little further on.

Spotted asparagus beetle larvae are typically darker in color than the common asparagus beetle larvae. Both are grey-green in color. Finding them requires close attention, as they blend in with the foliage of your plants.

Life Cycle

The beetle likes to overwinter in leaf litter or other debris near its food. It can even overwinter inside the hollow stems of older asparagus plants.

As spring comes, the adult beetle will also emerge from its winter hiding space. They start by having a snack to replenish themselves, feasting lightly on the tips of the new shoots.

Once satiated, adult asparagus beetles will begin laying brown, pill-shaped or oval eggs in neat rows. These will be either on the spears themselves (for the common asparagus beetle), or on the ferns or flowers (both types). It should be relatively easy to see these eggs as they visibly jut out from the fern or spear, creating an almost spiky-looking line along it.

The eggs hatch within three to eight days, and small larvae emerge. The common asparagus beetle larvae migrate to the ferns and begin to feast upon the plants. The spotted asparagus beetle’s larvae prefer the berries that are formed by the flowering plants.

Approximately two weeks after emerging from the egg, the larvae are now prepared for pupation. They drop from the plant down into the soil, dig under the surface, and form a cocoon there. It takes a week or two for the larvae to pupate and then emerge as adults to begin the cycle again.

Two to five life cycles can happen in a year’s time, depending on the weather conditions where the plants are. Colder climates have fewer life cycles.

Common Habitats

Both types of asparagus beetle inhabit North America, but the spotted asparagus beetle is far more common in the eastern half. The common asparagus beetle is present throughout the country.

As a general rule, the beetle spends the majority of its life around asparagus plants. What time isn’t spent around asparagus is generally spent trying to locate a new asparagus plant.

What Do Asparagus Beetles Eat?

While I would say the answer to this question is pretty obvious, it’s not. That’s because the spotted asparagus beetle is more culinarily diverse than its cousin.

Common asparagus beetles are fixated on only asparagus plants, which makes them a major problem for farmers of the crop. But the spotted asparagus beetle has been known to get a taste for cucurbits. It can occasionally lay eggs on the flowers of these plants, where larvae will snack on newly forming melons or squash.

However, it really prefers the berries of the asparagus fern. That’s why it’s most likely to be found there, where all its nutrition needs are fully met.

Holes or pits in the leaves, stalks, or plant structure indicate a beetle problem. These areas will turn brownish in color. The tips of the spears themselves may also turn brown. After excessive feeding, the plant may appear shriveled and stunted.

How To Get Rid Of Asparagus Beetles

Now that you know what you’re looking for and what it’s likely to be attacking, how do you eliminate these annoying little beetles from your perennial beds?

Organic Control

A spray insecticide can help you kill beetles and their larvae. But it’s best to use these options in limited amounts, especially on young asparagus stalks. Spot-treat when you discover adult or larval asparagus beetles, rather than doing widespread spraying when it’s not necessary.

Remember that some insecticides are harmful to bees. While there are options less dangerous to pollinators, avoid spraying the asparagus spears when the tops have gone to bloom.

Pyrethrin sprays are an option for asparagus beetle control. These work extremely well against most beetles, caterpillars, and a host of other common pests.

Environmental Control

Use beneficial insects to help keep the egg population down. Ladybugs and lacewings will happily eat the asparagus beetle eggs, preventing reproduction.

There is a beneficial parasitic wasp that is naturally attracted to asparagus in the wild. This tiny wasp, Tetrastichus asparagi, will lay its eggs in asparagus beetle larvae. When the eggs hatch, the larvae will be consumed by the young wasps. As long as you do not use any pesticides that are harmful to wasps, this insect will arrive on its own and take up residence nearby.

Birds love to eat both the adult form and the larvae of asparagus beetles. If your asparagus patch is bird-friendly, they will help you with asparagus beetle control.

Beneficial nematodes are another great thing to have in your soil. These microscopic soil organisms will help you by killing the larvae in their pupa beneath the surface of the soil or in leaf litter. They also protect against other pupating insects such as potato bugs, fungus gnats, and cutworms.

Preventing Asparagus Beetles

Watch your plants closely in late April and early May as the new stalks start to appear. Catch the overwintering adults quickly after they make their way out of the surrounding soil and hand-pick them off the plants to prevent egg laying.

Harvest spears as soon as they’ve reached a reasonable length to discourage beetles. If the adult beetle can’t eat the fresh asparagus tips, it won’t stick around. However, be check your plants as you harvest to ensure there are no eggs on the plant or on the stalks you’re cutting.

Use a soft-bristled brush to knock eggs and larvae off of the plant. Most larvae dislodged this way will lack the energy to climb back up and return to eating, dying on the soil’s surface.

If you’re sure you don’t have overwintering beetles in your soil, keep a floating row cover over your plants. After all, you don’t want to secure the plants with their natural predator right there!

Frequently Asked Questions