How to Identify and Deal With This Pest

Uncommon pests are the worst. Not always, of course. In large doses, even the most mundane pests are awful. But those rare, creepy, tiny pests that can wipe out your whole harvest without ever really catching your eye are terrifying.

They haunt the nightmares of farmers all across the world.

Sometimes, they even look the part. Symphylans – tiny, ghostly, soil-dwelling arthropods – look like slender drops of ectoplasm. But these slivers of white can be a powerfully destructive force in your garden. Once they invade, it’s hard to control them.

What Are Symphylans?

Tiny symphylans are distantly related to centipedes and millipedes. They’re not venomous. Most of them are herbivores. Eyeless and colorless, these pale, luminescent-looking arthropods run quickly through the soil. They’re rarely found above ground.

Symphylans live deep in the soil under rotting logs or large stones. Often, you’ll find symphylans in untended land like forests, fields, and near crumbling stone walls.

Since symphylans feed primarily on decaying vegetation, most species aren’t a problem in the garden. But, the nefarious garden symphylan can be a problem. It feeds on the crops that we grow.

The Garden Symphylan

In the garden, symphylans stop being just spectral feeders on decay and become destructive pests. The garden symphylan (Scutigellera immaculate) probably originated in Europe but has spread across most of the world.

Garden symphylans have 12 pairs of legs along their segmented body. They can grow up to six millimeters (0.2 inches) in length, which makes them very hard to see. Symphylans need humidity to survive. They like moist, loose soil because they don’t actually burrow. Instead, they slide through cracks in the soil.

Symphylans can only live in humid soil. If the soil humidity drops under about 75%, most symphylans will die off quickly. In the soil, symphylans feed on garden debris and plant roots.

It’s this feeding on plant roots that makes symphylans such destructive pests. Without ever being seen by you, an invasion of symphylans can wipe out your entire harvest. Garden symphylans tend to feed primarily on beets, lettuceand corn. But they will feed on the roots of almost every plant.

Habitat

Garden symphylans thrive in rich, heavy soil with plenty of organic matter. This soil is generally more moist than lighter soils. It also contains plenty of the composting plant matter that these pests love to feed on.

This heavy soil is also usually home to plenty of earthworms. Symphylans thrive alongside earthworms. They can use the small holes worms make to travel through the soil.

Remember, they also like it moist. That’s why they’re far more common in areas like the Pacific Northwest.

Life Cycle

Adult symphylans spend the winter months deep in the soil. Once the soil temperatures warm up to 45°F or more, the adults move up in the soil until they’re about six to ten inches below the surface. Symphylans hate light, so they’ll never willingly go too close to the surface.

Females lay their eggs near the surface. The eggs hatch about 2 to 3 weeks after laying. The newly hatched nymphs look like miniature adults but with six pairs of legs.

As they grow, the nymphs go through regular molts. After each molt, the nymphs gain another pair of legs until they reach adulthood.

The whole molting process takes about three months. During this time, the nymphs hungrily eat away at everything they can find.

After maturing into 24-legged eating machines, adults stick around, munching up all the decomposing plant matter and new root growth they can find. When soil temperatures dip below 45 °F, the adults retreat back into the soil to await spring.

Symphylan Damage

Seedlings and young plants are at the greatest risk from symphylans. Since they love to eat new root growth, they can weaken or destroy seedlings quickly. The young plants just aren’t mature enough to recover from the loss of new root growth.

Once these pests start feeding on your seedlings, the young plants become stunted. They don’t grow as fast as unaffected plants. Soon, they’ll start looking sickly and weak. Often the seedling never recovers.

In older plants, you’ll start to notice that the plants are stunted, weaker, and less vigorous than they used to be. If you look at the roots, you’ll see gnarled corky growth over small holes. The root will often look twisted. Affected roots are often tough as well. With a scarred, pock-marked texture.

Root crops affected by symphylans are usually smaller, tougher, and uglier than non-affected roots. The corky holes have to be cut away before eating, and often, the whole root is inedible.

Symphylan Control

Unfortunately, there’s no way to effectively treat a symphylan problem while your plants are growing. If your crops are showing signs of damage, start by checking for active symphylans in the soil.

To do this, turn over at least ten shovel-fulls of soil and sift through each one. Look closely for active symphylans. Remember that they’ll want to move quickly away from the light.

If you see an average of one symphylan per shovel of soil, you have enough of a problem that you should treat the area before planting in it again.

In a large field, check a few different areas and mark off the affected parts for treatment. You don’t have to treat the entire field, symphylan infestations are usually contained in small areas.

Control Tillage

One of the best ways to control an invasion is by frequently and deeply tilling the soil. Shallow tilling won’t work here because symphylans can move quickly and they tend to live deep in the soil.

Of course, you can’t til while trying to grow crops. But after harvest – or if you lose your crop to symphylan damage – till up the soil. Tilling not only breaks up the soil, but it also seals off the tunnels your symphylans were using to get around.

Tilling can also kill a few of the symphylans, though they’re small enough to avoid much damage.

If you consistently till up your soil into very fine, seed bed soil, you will help to break up their tunnels. This will kill some of them. It will also expose more of the soil to the air, reducing the soil humidity and killing off symphylans that way.

But, tillage is never completely effective. You just can’t till deep enough to damage all the arthropods. Some of them are close to the surface, some aren’t.

It is always best to till the soil in warm weather, when the symphylans are closer to the surface of the soil, but even then, there will be some out of reach.

Insecticides For Symphylan Control

Another way to manage your symphylan problem is with insecticides. But using insecticides to treat this pest is a bit more complicated than using them for above ground pests, since they hide underground.

Symphylans aren’t insects, and they don’t hang out on the surface of the soil where you can spray them. To treat an infestation with an insecticide, you’ll have to work it into the soil.

Not all insecticides will kill symphylans. But most of them should repel the arthropods from the soil. For the insecticide to be effective, you have to work it into the soil. The best way to do this is to broadcast the insecticide across the affected area, and then till it into the soil before planting.

If you practice low or no-till methods of growing, there are granular insecticides that you can apply. They aren’t quite as effective as broadcasted insecticides, but they will help.

Only one organically approved insecticide has managed to consistently repel symphylans. Aza-direct has successfully and consistently repelled these pests as an organically approved insecticide.

If you’re not interested in growing organically, the insecticides Capture and Mustang have had good results as well.

Other Control Options

While symphylans can feed on a wide variety of crops, crop rotation can discourage them. Potatoes and spring oats can reduce the population of symphylans slightly.

In gardens and other small-scale growing operations, raised beds can help to keep your plant roots out of reach of most arthropods. Especially if there is a barrier of some sort between the raised bed and the ground.

Some farmers have tried flooding their fields to drown out the pest population. In this method, farmers flood a field for two or three weeks in the spring and in the fall to drown these pests. But the jury is still out as to the efficacy of flooding.

It can take a lot of water and a lot of work to flood a field for three weeks. The water has to soak into the soil at least three feet below the surface to be effective against the symphylans.

All too often, the pest population decreases after flood only to swell again a year later