University of Vermont Extension
Department of Plant and Soil Science
Dr. Leonard Perry, Extension Professor
University of Vermont
Nematodes are very tiny,
microscopic “worms” that mostly live in soils, although “foliar”
in leaves. While some species harm plant
roots, others are beneficial by attacking and killing pests such as
our lawns and gardens. They are easily
applied, but the right timing and conditions are needed for them to
nematodes are becoming much more popular for soil pest control. They
over 200 pests from up to 100 insect families.
These pests are ones that either directly injure our desired lawn or
plants, or immature grub stages of insects before they mature to
Being natural, beneficial nematodes
are safe to use around humans, children and pets. Being natural,
they’re safe too for soils and
wont harm non-target organisms such as bees or pollinators. They’re
easy to apply (no protective gear is
needed), quick to work (often within a couple days), and cost
effective. While you may need 20,000 or so to treat a
square foot, they are so small that for under $20 you should get
million—enough to treat 1,500 square feet.
“mode of action” of beneficial nematodes is like something from a
(at least for the target pests). Once
applied, the tiny juvenile stages seek out their specific prey. One
uses an ambush strategy, waiting for the prey to come close before
attacking. Another nematode (Heterorhabdtis) uses a
strategy, seeking out and destroying pests.
They either follow the trail of excrement of the pest, or seek it
in temperature and carbon dioxide levels.
found, the beneficial nematodes enter the grub or other pest through
body openings, such as the mouth or openings to the breathing
tubes (“spiracles”). These juveniles
carry a bacterium (safe for plants and the environment) that they
the pest blood. These bacteria multiply,
killing the pest in two days or often sooner, and converting host
food for the nematodes. Since these
bacteria work to help their host-- the nematodes-- they are called
change from a beige-white to reddish brown when infected, die and
and are soon hard to even find. The
nematodes feed on the dead pest from within (hence they are called
“entomopathogenic”), and can go through several generations of
adults in a
couple weeks. Once their food source is
gone they exit and move on to new prey.
are a couple main types of nematodes you’ll find (Steinernema,
Heterorhabdtis), and a couple or more species of
each. Each targets specific pests, so it
helps to know what pests you have in order to buy the right
nematode. For instance, one species of the former (S.
carpocapsae) is effective on larval
stages of armyworm, weevils such as black vine, caterpillars,
cutworm, and sod
webworm. Another species (S. feltiae) is used for larvae of
cabbage maggot, onion maggot, raspberry crown borer, and thrips.
Both species are effective on larvae of codling
moth, corn earworm, and cucumber beetle. You’ll want a species (H.
bacteriophora) of the other nematode
for larvae of tree and vine borers, European chafer, Colorado potato
corn root worm, flea beetles, and grubs including those of the
and ones damaging lawns.
Your local garden center, master gardener
programs, online resources, books, and state extension diagnostic
are all good resources to identify target pests. Labels and online
descriptions will then
guide you to the appropriate nematode product.
If you’re not sure what pest you have, you may need to apply a
different nematode products.
type can affect the nematodes. Some work
best in cultivated soil (Steinernema)
while others work best in undisturbed soils (Heterorhabdtis).
species works best in clay or silt (S.
feltiae), another works best in sandy soils (S. carpocapsae).
isn’t crucial for the other main beneficial nematode (Heterorhabdtis).
you’ve chosen the right product, to be effective you must apply it
properly. Timing of the season is
important, as the soil stages of your target pest need to be present
nematodes to work on them. Late summer
into early fall is a good time for many grubs of plants, crops, and
lawns. This is a great time for lawn grubs, as then
they are usually small, with thin skins the nematodes can penetrate,
they’re feeding on grass roots near the soil surface. It is when
armyworms fall to the ground to
change stages (pupate) as well.
that the nematodes are living organisms, so should be applied very
you get them. They like moisture, so if
it hasn’t rained, water thoroughly both before and after
application. You can apply during the rain too. If they come on a
wet sponge, rinse them from
this into cool water. Then use this as a
concentrate to water or spray on according to label directions.
Then keep the soil moist for a week to 10
days after, if it doesn’t rain.
overcast weather is good for another reason—nematodes are quite
the UV in sunlight, and can be killed within a minute or two if
it. So you’ll often see recommended to
apply in early morning or late afternoon.
They’re sensitive to temperature too, with ideal temperatures
and 100 degrees (F).
prevention, you can apply 2 to 3 times a year, such as in spring,
fall. For control of existing pests,
apply every 2 weeks until the infestation lessens or goes away.