Be a Better Farmer: Understand
the Living Soil
Part 3 - The Good, the Bad, and the Ugly
Originally Printed in Country Guide, Spring 2001
Table of Contents
- Introduction
- Wood Lice (Sow Bugs and Pill Bugs)
- Slugs
- Rove Beetle
- Encourage the Good Bugs!
- Related Links
Introduction
Don't be deceived by appearances: that ugly-looking bug might be
your friend.
Take the time to look, and you'll spot many insects and other creatures
living in or on your soil. But most farmers know precious little
about this teeming life just below their feet. Maybe that's because
they figure there are too many different organisms for anyone to
recognize them all.
For sure, countless life forms do inhabit our soils. But some are
common, easily identified, and worth getting to know. This installment
of our "living soil" series looks at some more of the
ugly but interesting soil denizens: wood lice, slugs and rove beetles.
Shy moisture-loving creatures, they're often broadly labelled as
"bugs". Only one is a true insect.
Wood Lice (Sow Bugs and Pill Bugs)
Wood lice are grouped into 2 main categories: pill bugs and sow
bugs. Both are very beneficial to the soil as decomposers. They
feed on dead and rotting plant materials. Wood lice shred organic
material, aiding further breakdown. Opportunistic feeders, they
eat carrion, some insect eggs and other molting wood lice.
Often thought to be an insect, they are actually crustaceans, like
crabs and lobsters. They need to stay moist and usually live under
plant residues, logs, rocks and in other dark damp places. You can
find these armadillo-like creatures throughout the topsoil layer,
especially in no-till fields with well-developed macropores or in
soils with an open structure and lots of cracks.
Sow bugs have 2 pointy tailpieces called uropods that they can
use to take up water. Pill bugs have shorter uropods which don't
help get water but do allow the bugs to curl up into a ball if threatened.
Wood lice are important in many ecosystems. They are food for frogs,
toads and many small mammals. With an affinity for heavy metals
(copper replaces iron in the oxygen-carrying pigment in their blood),
they have been used as environmental indicators in Europe.
Slugs
Slugs, on the other hand, are pests! This is old news for most
no-tillers, and the 2000 crop year was a good one for slugs. They
feed on living or dead plant material, and cause severe damage to
corn and soybeans at germination and in the early growth stages
-- particularly on no-till fields in wet years.
It's hard to confuse slugs with any other pest. Their telltale
silvery slime trails are a dead giveaway. Feeding damage is also
characteristic. Slugs feed by rasping the plant surface with a tooth-covered
tongue called a radula. Crops show holes or shredded sections resembling
hail damage. If slug populations are high, they may also feed on
germinating seeds. Corn can usually grow out of the injury, as the
growing point is not affected.
Slugs are actually snails without shells. Their soft bodies desiccate
(dry out) easily The ideal slug environment is cool and moist, with
temperatures between 18° and 20°C and relative humidity
at 100%. So for obvious reasons, high-residue conditions favour
this crop-eater.
Slugs are active at night or on cloudy, high-humidity days. They
feed every second day and are most active in the spring, early summer
and early fall. Under the dry hot conditions of mid- summer, slugs
go into a dormant state.
Control measures, such as removing decaying crop residue from the
row area, help in some years. Slug baits are generally expensive
and practicable only in home garden situations. Some growers have
achieved a level of slug control in no-till systems through application
of a 10% solution of 28% nitrogen several times, either early in
the morning or at dusk when the slugs are active and exposed.
Control from 28% nitrogen is variable, however, since the solution
acts as a dehydrator and must make contact with the slugs to be
effective. Application must occur when slugs are exposed. Unfortunately,
by hiding in soil debris and feeding only every other day; they
easily avoid contact with the spray.
Rove Beetle
The rove beetle is another beneficial soil creature. This insect,
found in or near decaying plant or animal matter, feeds on other
insects, particularly larval stages like carrot maggot. Some species
of rove beetle feed on crop pests like spider mites and aphids on
low-growing crops such as strawberries. These slender elongated
beetles are very common, but often go unnoticed. They are generally
black or brown and can range in size from very tiny to over one
inch in length. Larvae look much like the adults without wings.
This is very active insect. Rove beetles generally run when disturbed,
raising the tip of their abdomen in similar fashion to scorpions.
They are also good fliers, especially under warm conditions. They
hide in the soil and under plant debris during the day; and are
most active at night.
Encourage the Good Bugs!
It makes sense for farmers to encourage both wood lice and rove
beetles in the soil. They help to cycle organic matter and nutrients,
and reduce pest populations. Like all living things, they need habitat
and food. So cropping systems that provide moist, cool soil with
lots of decaying residue (reduced tillage, for example) encourage
populations.
For more information on identification and management of soil bugs,
refer to OMAFRA publications, including: Agronomy Guide for Field
Crops (Publication 811), and Field Crop Protection Guide (Publication
812).
Related Links
