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.
("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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
from the University of Massachusetts Extension, 1999