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University
of Rhode Island GreenShare Factsheets
Biological
Control of Turf Insects
Many
turf managers are looking for ways to reduce their dependence on
traditional insecticides and to incorporate more "biopesticides"
or other biological control options into their insect control programs.
"Biopesticides" are living organisms which are handled and applied
in a manner similar to traditional insecticides. Examples include
entomopathogenic nematodes, bacteria, and fungi. Entomopathogenic
("entomo" = insect; "pathogenic" = causes disease)
nematodes are nematodes which carry bacteria inside their bodies.
When the nematode penetrates an insect victim, it releases bacteria,
which break down the internal tissues of the target insect, resulting
in a massive infection ("septicemia"). As the insect dies, the
nematodes reproduce within the cadaver. The juvenile nematodes
pick up some
of the bacteria, and move on in search of new target insects. Entomopathogenic
nematodes are available commercially and appear to be effective
at suppressing populations of several turf insects. The most common
commercially available nematode is Steinernema carpocapsae,
available under a variety of trade names and formulations. This
nematode appears to be effective against various turf caterpillars,
such as webworms and cutworms, as long as the nematodes are applied
when the caterpillars are still relatively small (less than half
an inch long). The nematodes are sensitive to desiccation, so applications
should not be made in the middle of the day and should be watered
in immediately, either with irrigation or rainfall. Other
species of nematodes are under development for use against white
grubs. The one which shows most promise is Steinernema glaseri,
which has reduced grub populations 50 to 70% consistently over several
years of testing. However, this nematode is a bit larger than its
cousin, S. carpocapsae, and has proven difficult to produce
in a form which can be applied through traditional application equipment.
Entomopathogenic
nematodes are being used to suppress populations of many different
kinds of insects. One species is proving very effective against
mole crickets in Florida and the southeastern United States. Another
is being used to control fungus gnats in greenhouses and mosquitoes
in certain outdoor settings. Still another shows promise against
black vine weevil larvae in nursery settings. Some
bacteria cause diseases in insects. The most common bacterium used
against turf insects in Bacillus thuringiensis var. kurstaki,
or "Bt," for short. It is effective against several kinds of caterpillars.
Bt is much less sensitive to desiccation than the nematodes, so
can be used as a foliar spray against caterpillars like the gypsy
moth as well as cutworms and webworms in turf. Bt produces a toxin
which paralyzes the insect gut, so the insect stops feeding shortly
after ingesting treated plant material (although it may not die
for several days). Bt works much more slowly than most traditional
insecticides, and should be applied when the target caterpillars
are still relatively small (less than half an inch). The strain
of Bt used against caterpillars is quite specific, and so does
not
interfere with most of the beneficial insects in the area. A
new strain of Bt (var. japonensis and called "bui bui")
appears to be effective against some species of white grubs. The
product
has not been tested widely in field conditions, and is not expected
to be available commercially for several years. This strain of
Bt
appears to be on of the strongest candidates for biological control
of white grubs. Another
species of bacterium causes a disease in Japanese beetle grubs.
Bacillus popilliae causes "milky disease" in the grubs. Infected
grubs take on a very milky appearance and are very flaccid. Use
of milky disease in New England is somewhat controversial, because
there are no data to indicate whether the disease actually suppresses
grub populations. If the disease becomes established, it usually
takes a few months to have a noticeable effect on the grubs in the
area, but may remain "active" for three to five years in that area. B. popilliae is specific to Japanese beetle grubs and seems
to have little effect on other grub species, such as the European
chafer or oriental beetle larvae, which also damage turf. Milky
disease is available commercially, but there have been some problems
with quality control in recent years. One company produces the bacterium
by collecting grubs in the field, bringing them back to the laboratory,
infecting them with Bacillus spores, and grinding up the
infected grubs. This process is labor intensive and expensive, but
works quite well, so the quality control is very good. Some fungi cause
diseases in or on insect bodies. Several such fungi occur naturally
in New England, and others are being developed in
laboratory settings after having been located in other parts of
the world. One of the "native" fungi is Beauveria bassiana,
which attacks chinchbugs and billbugs in turf settings in New England.
Particularly in cool, wet springs these insects may be found covered
with tiny strands of materials that looks like cotton candy. These
strands are mycelia of the fungus, which has invaded the insect
body and attacked the internal tissue. At least one company is not
marketing a strain of this fungus, which may suppress chinchbug
or billbug populations in the field settings. Another
fungus, Metarhizium anisopliae, appears to be quite effective
against white grubs in the soil. The main challenge currently is
to find a way to "package" the fungus so that it is not sensitive
to sunlight and can be applied through conventional application
equipment. Several companies have shown interest in this fungus,
and it should be available commercially by the end of the century. Insect growth regulators
(IGRs) are chemicals which occur naturally within an insect,
governing the natural molting process. In some
cases an IGR will signal an insect that it is not time to make
the final molt to the adult stage. As long as such an IGR is
present,
the insect will not molt to an adult. It may complete a few "extra" molts
as an immature, but will not become an adult. As a result it is
unable to reproduce, and ultimately the reproductive cycle
is interrupted. Most IGRs of this sort are very specific, governing
the actions of a particular species or group of closely related
insects. Several IGRs have been developed for such insects as whiteflies
and mosquitoes, and at least one is being tested for white grubs. Other
IGRs are more general in their action. Azadirachtin, a derivative
of the neem tree, is a growth regulator which appears to interfere
with a part of the molting process in which an insect develops
new
chitin for the exoskeleton ("outer shell"). Insects which have
been exposed to azadirachtin exhibit some peculiar shapes, such
as half
larva and half pupa or half pupa and half adult. The end result
is the same--healthy adults do not emerge. Finally, there
are some species of grasses which contain endophytes, which are
fungi which produce substances which are toxic to certain insects.
Endophytes occur in some perennial ryegrasses and fescues, and have
been incorporated into some commercial cultivars. They are effective
in the suppression of chinchbugs and billbug populations, and are
active against cutworms and webworms as well. Turf managers who
are looking at renovating turf areas should consider including some
endophtic grasses in the renovation. Note that endophytes are also
toxic to grazing stock, such as sheep and cattle, and so should
not be used in pasture settings. See GreenShare
Factsheet on Endophyte-enhanced grasses for more information.
Adapted
from the University of Massachusetts Extension, 1999
Pesticides
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
For more
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
University
of Rhode Island Cooperative Extension provides equal program
opportunities.
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