Be a Better Farmer: Understand
the Living Soil
Part 2 - Good Bug or Bad?
Originally Printed in Country Guide, Spring 2001
Table of Contents
This second installment in our living soil series focuses on 4 soil-dwelling creatures that often get confused with each other. It is important to be able to identify them, however, so you know whether to control them or help them thrive.
The bad actor in this group is the wireworm. A crop pest, it feeds on seeds, germinating seedlings and roots of corn, soybeans, wheat and edible beans.
Often confused with millipedes and centipedes, wireworms are the larvae of click beetles, which you may fine attracted to lit areas around your house in late July. These adults do not damage crops.
The larvae have long, hard cylindrical bodies that are copper-brown in colour. True insects, they have only 3 pairs of legs. Click beetles can have a long life cycle, some remaining as larvae and potentially doing damage for 3 to 5 years. So if they were there the previous season, they'll probably still be in your field this year. They prefer reduced or no-till fields, sandier soils or fields where sod, small grains or alfalfa have been plowed under.
Seed treatments containing lindane protect germinating seed against this pest. If populations are high, an in-furrow or banded insecticide may be needed to protect the growing seedling. No rescue treatment is available.
Millipedes, in contrast, are beneficial. They shred organic matter and mix it through the soil. This gives smaller soil organisms like fungi and bacteria greater surface area to work on, and speeds residue breakdown.
Millipedes have hard cylindrical bodies, usually dark brown, gray or black in colour, and between 30 and 400 pairs of short legs. When disturbed, they usually curl up. They're easily confused with wireworms and centipedes. The key here is the number of legs and the body shape.
Absolutely harmless to humans and buildings, they may occasionally feed on garden plants if a garden is over-watered or has high amounts of plant debris and rotting material on the surface. But take a walk at dark to make sure the damage isn't caused by earwigs.
Because millipedes need moist, cool soil with lots of decaying residues, they respond well to reduced tillage.
Centipedes are also good (but ugly) bugs. These predators feed on pests such as slugs, symphylans, spiders, flies and cockroaches. Usually yellow to reddish brown, they're flat-bodied and have one pair of long legs per body segment. With at least 15 pairs of legs, centipedes are not true insects. They are rather shy and run very fast when found.
Their favoured habitat is dark, moist, protected areas under leaves, logs and residue. As with millipedes, farming systems that leave crop residues on the soil surface and involve a variety of crop rotations will encourage centipede populations.
Often confused with millipedes, centipedes can be identified by their flat body shape and leg arrangement. They won't harm humans or buildings. Centipedes are actually good to have in your house. They hunt less welcome visitors like cockroaches and spiders.
Fourth on our list come symphylans. These bugs are both good and bad. Occasional pests of corn, they feed on germinating seed, gouging kernels. They may also feed on roots and root hairs of corn, alfalfa, carrots, and potatoes.
On the other hand, they mostly survive by scavenging nutrients from plant debris. By shredding residue for faster breakdown, they keep plant nutrients cycling through the soil.
You'll find symphylans in damp, high-organic, sandy soils usually when crops are germinating slowly from a cool, wet spring. They are small (usually less than 1.5 cm long), white to brass coloured, and have only 12 pairs of legs (one pair per segment like centipedes). Their distinctive antennae are jointed to form a Y shape. They are often confused with wireworms and centipedes.
It's not known whether symphylans can be controlled with seed- or soil- applied treatments, but they seldom reach crop-pest levels in Ontario. A steady supply of crop residues and less soil disturbance (no-till) encourages these creatures to be good soil citizens.
Since many of the good critters in your soil look like bad guys and vice versa, it's important to recognize them all.
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