Detection
and management of thatch dwelling worms such as webworms, armyworms and
cutworms are essentially the same.
Because the brown patches caused by these worms can superficially
resemble those caused by other pest
insects or diseases, accurate diagnosis is important. Mature armyworm
caterpillars are 1 1/2 - 2 inches long, and vary in color from grey to
yellowish green. Light stripes run the length of their
bodies. Monitoring or detecting armyworms can be accomplished by visually
examining the thatch layer or by using a
soap drench to flush them out.
Thatch-dwelling insects such as armyworms can be found in the layer of dead grass just above the soil line. They are present if: grass blades in the damaged
area are actually missing and not just dead; there are green fecal pellets in
the thatch; you find larvae in
silk-lined tubes in the thatch. You can
use a small hand trowel to loosen the thatch. Soap drenches are a useful tool
for monitoring and detection. To do
this: Mark off two or three 2 feet square
sections of lawn in both damaged and undamaged areas. Mix 2 tablespoons of liquid soap or detergent in 1 gallon of
water in a sprinkling can, then pour the mix evenly over each area to be
sampled. The soap irritates the caterpillars, causing them to crawl to the
surface. Keep a close watch on each
test area for about 10 minutes. Brief
movements alone may indicate the worms are present. Where the thatch is thick,
it may be necessary to pour several more gallons of soap solution on the test
area to reach the worms. If the thatch
is saturated but no catapillars appear, the damage is probably due to disease or
another type of insect.
If
your lawn is in good condition and growing vigorously, the presence of 2 or 3
worm larvae per square foot is probably
not cause for concern. If your lawn is
under stress, the presence of as few as 1 larva per square foot usually
indicates the need for treatment.
Indirect
strategies for armyworm control include planting resistant grass varieties,
managing horticultural stresses on your
lawn and conserving native biological controls. Kentucky bluegrass variety "Windsor" and
"Park" show some tolerance for thatch-dwelling worms. If thatch dwelling worms are a chronic problem,
however, you should consider replacing grasses with Indophytic grasses (grasses
that contain beneficial fungi within their tissues). Grasses with endopytic fungi that repel caterpillars or worms include the perennial ryegrass
types: Citation II, Commander, Penant, Regal, Repell, Sunrise, turf type tall
fescue grass types include: Apache and Kentucky 31. Check with your local distributor
for others. Reducing the horitcultural stresses on lawns inlude reducing the
thatch level in your lawn if it is thicker
than 1/2- 3/4 inch. Over fertilizing,
fertilizing at the wrong time or poor watering techniques can cause thatch
build up. Natural organic fertilizers
are preferable because they provide food for both soil and plants over time,
build up the soil water infiltration rate, increase water holding capacity, and
make your lawn healthier. Good lawn
management should encourage the presence of the natural enemies of
thatch-dwelling worms. Certain ants,
flies, spiders, vespid wasps, native earwigs, bettles and birds prey on these
pests.
Direct
control includes soap drenches and raking to remove moderate populations. For
higher populations beneficial nematodes may control the infestation or an
application of the microbial insecticide Bacillus Thuringensis (BT).
The
key lies in maintaining a healthy soil.
Pesticides and synthetic fertilizers kill natural soil organisms that
are essential for healthy soil. Without
a healthy soil, your grass will become dependent on expensive, toxic quick
fixes that cause a host of problems for your lawn. Synthetic fast release
chemical fertilizers are problematic because they: leach from the soil quickly,
run-off into streams or groundwater, burn grass because their nitrogen is too hot,
provide no food for soil microorganisms or earthworms, repel worms because they acidify the soil,
slow down bilogical activity in the soil, increase susceptibility to pests and
disease, increase soil compaction, lesson organic material so that soil structure
declines, reduce water holding capacity of the soil, and lead to chemical
addiction where more chemicals must be added with every application. Using organic lawn care methods will make
your lawn care job easier over time because it will make your lawn healthier,
less weedy, and more disease and pest resistant.
Sources: 1.Common Sense Pest Control, William
Olkowski, Sheila Daar & Helga Olkowski
2. Preserve Your Lawn's Health with Organic Lawn Care
by Charyn Grandau,
Education/Resource Conservationist; Soil and Water
Conservation District,
St. Louis County
Missouri-SMPL,
Inc.
PO
Box 27
Morse
Mill, Missouri 63066-0027