University of Vermont
Department of Plant and Soil Science
LAWNS: THE PEST PARADE
Dr. Leonard Perry, Horticulture Professor
University of Vermont
If you maintain a lawn, you may encounter several key pests during the
summer. Knowing which pests you have from the symptoms they cause, how
to control them, and even if control is needed, will ensure you keep a
healthy lawn with no negative environmental impact.
In his book, The Lawn Bible, author (and Fenway Park master
groundskeeper) David Mellor makes the important point that lawns are teeming
with insects, most either beneficial (eating the bad insects, nature’s “pest
patrol” as he puts it), or causing no harm. The few bad insects get
all the attention and, by trying to control all insects, you may be killing
helpful ones and many innocent bystanders. The bottom line: you
don’t want an insect-free lawn.
There are specific types of damage—symptoms—to watch for from the
undesirable lawn pests, each narrowing down your choice of culprit.
Underground insects destroy the roots, so the plant dies from being unable
to take up water and nutrients. Other insects feed on the “crown” of
grass plants—the part at the soil surface from which the grass leaf blades
arise. Others either chew leaves and stems or, in the case of chinch
bugs, suck the nutrients out of the grass blades. Other pests such as
skunks and raccoons dig up lawns in search of underground insects.
Since several lawn problems masquerade as those from pests, but are from
culture, you’ll need to get right up close and inspect your grass on hands
and knees for pests. Grass injured from drought or diseases may, at
first, appear to be from insects. A dull mower blade may tear and
brown grass blades, appearing as if chewed by insects.
Since pests feed on live grass, any insects you find in dead patches likely
are not to blame. Look on grass blades, at the plant crowns, and in
the thatch layer (the layer of organic dead and living plant parts at the
soil surface) for lots of the same pest. Get a spade and gently lift a
section of turf to see if any are feeding below ground. If the turf
pulls up in your hand without any help from a spade, you likely have a grub
Once you’ve determined you have lawn pests, you need to identify them.
There are many online resources for such, or check with your local
full-service garden center, Extension master gardener helpline (www.ahs.org/gardening-resources/master-gardeners),
or plant diagnostic clinic (www.nepdn.org/home).
Just because you have a known pest still doesn’t mean you must control
it. Just a few munching on your grass won’t cause much problem and you
can coexist with them. Consider options to deter pests from feeding,
and least toxic products.
Chemical controls are abundant, often seen advertised, and can be quite
toxic as well to beneficial insects, wildlife such as pollinators and fish,
your pets, and even your family. Common ones you’ll see include the
ingredient diazinon for chinch bugs, cutworms, billbugs, white grubs, and
sod webworms. Other products may contain the toxic ingredient carbaryl
for white grubs and billbugs. Usually found in the product Sevin, carbaryl
is one of the most widely used pesticides and is one of the most toxic to
bees. For any controls, chemical or otherwise, make sure to read and
follow label directions to ensure their safe and effective use.
Biodegradable, and nontoxic to humans, are insecticidal soaps. These
come from salts of fatty acids, and are used on soft-bodied pests such as
white grubs, chinch bugs, billbugs, and sod webworms.
Increasingly popular are botanical insecticides made from plant
materials. They break down quickly, so must come into contact with the
pest soon, and are not very effective on underground pests. Pyrethrin
products derive from the chrysanthemum plant, and should be used carefully
as they kill beneficial insects too, as well as fish.
Biological controls are those that use one organism to fight another.
Since they are living, make sure to follow the label on their storage and
use so they don’t die. Beneficial nematodes are microorganisms that
attack larvae of such soil pests as white grubs (Japanese beetles),
cutworms, and sod webworms. “Bt” is the common name for a bacterium
that kills some of these same soil pests. Endophytic fungi are
actually beneficial diseases that live within the grass plant, producing
natural compounds toxic to pests and deterring those that chew. You
can buy some grass seeds already inoculated with them; look for the word
“endophyte” on labels.
The key pests your lawn may encounter are those already mentioned above
under controls. White grubs are the larvae stage of any of several
beetles that live in the soil. They’ve been described as small
C-shaped white croissants with legs, and brown or yellow heads. They
cause irregular shaped dead patches of turf, usually in late spring or early
fall, which easily peel up like a rug. Digging for these by skunks is
another sign you have them.
You need to treat for white grubs when you find six or more grubs per square
foot of soil. Use a spade to gently lift a square foot section of
turf. Stir around the exposed soil to a depth of two inches, and count
the grubs you find.
Mature sod webworms are grayish caterpillars, about 3/4-inch long when
mature. You’ll probably see the moths first, which lay the eggs,
flying up as you mow. These larvae live in silky webbed tunnels (hence
the name) in thatch by day, and feed by night. If you have small, up
to two-inch, patches of dead grass, the blades chewed off just above the
thatch layer, you should see these by flashlight feeding at night.
Treat sod webworms if you have more than 15 per square foot. To find
out, flush them out, literally. Mix two tablespoons of dish detergent
(lemon-scented is best) with a gallon of water and saturate a two-foot
square area of lawn. In about five minutes, count how many webworms
have come to the surface.
Adult billbugs are small weevils—a type of beetle—about 1/8-inch long.
They are elongated, black, and have long snouts. The larvae or grubs
in soil, which cause the damage, are white, legless, and have orange-brown
heads. They cause circular dead spots where grass stems lift easily
away from the crowns. Do a “tug test”. Pull on dead grass stems,
and if they easily break off at the crown, this is a good clue to billbugs
and not sod webworms. Look in the crown and around roots for debris
resembling sawdust—another billbug clue. Check the soil as you would
for white grubs, and treat if more than one larva per square foot.
Adult chinch bugs are small, only about 1/5-inch long, with black bodies and
white wings. They have a distinctive triangular-shaped mark on each
wing. They produce large, circular, yellow to brown patches of turf
from sucking the juices out of plant parts. To see if you have these,
and sufficient numbers to treat, get a bottomless coffee can. Push it
two inches into the soil at the edge of an affected area, and fill the can
with warm water. Any chinch bugs will float to the surface in 10
minutes or so. Do this on the edge of several affected areas.
If, on average, you figure you have 15 to 20 chinch bugs per square foot,
it’s time to treat.
Cutworms are moth larvae that curl up into a tight circle when
disturbed. They’re plump, up to two-inches long, and either brown,
black, or gray. They cut the grass blades off at soil level, hence
their name. Usually it takes many to damage a lawn. Use the dish
detergent test to bring them to the surface and, if you count more than 10
larvae per square foot, it’s control time.
More on these pests, others, lawn diseases, and culture for a healthy
lawn, can be found in the book by David Mellor. A healthy lawn will
better resist pests, and recover more quickly.
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