Quick Facts...
- Black grass bugs are
native to western rangelands and exist at low populations on native
range.
- Severe infestations
are primarily associated with rangeland reseeded to introduced
wheatgrasses. Problems are especially obvious on roadsides seeded with
wheatgrasses.
- Black grass bugs
compete directly with livestock for forage grasses and may be major problems
in some areas and years.
- Cultural and chemical
control measures may be effective for many seasons if timed correctly.
Black grass bugs have caused considerable damage to certain western range
grasses over many years. These small black true bugs are native to western
rangeland, being first collected by the Hayden expedition in Colorado in
1871. The bugs apparently caused little damage to native plants before
rangeland improvements were attempted. The first reports of damage to range
grasses were in 1938, when many western ranges were seeded with introduced
wheatgrasses. Monocultures of these grasses provided a habitat that was
conducive to population explosions. Losses in heavily infested range may
exceed 90 percent of the forage. Even moderate infestations of black grass
bugs may offer significant competition with livestock for rangeland forage.
Several species of black grass bugs exist in Colorado, with the most
common being Labops hesperius Uhler. A second species, Irbisia
brachycera (Uhler) may be locally abundant. Thirty-four species of Labops
and Irbisia are known from North America. Black grass bugs are about
1/4 inch in length when mature and black in color over most of the body. L.
hesperius has buff coloration on the outer margins of the wing covers. I.
brachycera is jet black in color, with no markings. Immature stages are
similar in appearance to the adults, but smaller.
Black grass bugs damage plants in the spring by piercing and sucking the
contents of cells. Within seconds of the start of feeding, a whitish spot
appears at the site from the destruction or removal of chlorophyll. The bugs
begin feeding at the leaf tip and proceed downwards, feeding with the head
pointing down. Most feeding is done on the upper surface of the leaf. Damaged
leaves may appear straw colored, as if they have been damaged by frost.
Certain amounts of damage to the leaves seem to repel cattle or make the
grass unpalatable. Heavy infestations may prevent seed formation, and black
grass bugs often are pests of grass seed production fields. Most damaged
plants will eventually recover if there is adequate moisture, but drought
conditions coupled with severe black grass bug damage may cause some plant
mortality.
The host range of black grass bugs is quite broad. They feed primarily on
grasses, but will feed on some broadleaf plants in the absence of
grasses.There are definite host preferences, with wheatgrasses being among
the most preferred species. A time delay of four to seven years usually
exists between the reseeding of a pasture and the appearance of significant
numbers of black grass bugs. It appears that infestations are due to
increases in populations already in an area, and not from dispersal from
other areas.
The life history of black grass bugs allows several management strategies
to be effective. The winter is spent as an egg laid in the stems of host
grasses. The eggs hatch in the spring when the grasses begin to grow. Egg
hatch occurs early in the spring at lower elevations, and progressively later
at higher elevations. One generation of black grass bugs is produced each
year. Nymphs feed and molt five times before becoming adults. It usually
takes four to five weeks from egg hatch to the appearance of adult insects.
Bug numbers begin to decline about four weeks after adults appear as they lay
eggs and then die. The time span of the population is regulated by
temperature, with adults maturing more quickly at higher temperatures. Most
females in a population do not have fully developed wings, which means they do
not readily disperse to and colonize new areas.
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| Figure 1: Labops black grass bug. The whitish flecking of the leaf is typical black grass bug damage. |
It is important to identify an infestation of black grass bugs early in
the spring so chemical control measures may be applied before extensive
damage is done or egg laying begins. insecticides will kill the adult bugs
but will have no effect on eggs laid in grass stems. If enough eggs are
present, a reinfestation may occur in the next growing season. One well timed
application of insecticide may reduce bug numbers to a non-economic level for
many years. If control is successful, the insecticide cost is spread over
many years. Several insecticides are labeled for black grass bug control on
rangeland and grass seed production.
Timely grazing or burning dead grasses in the fall are management
techniques that destroy black grass bug eggs
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| Figure 2: Grass severely
affected by black grass bug feeding. Note the general whitish appearance of
the foliage. |
and may limit the need of
chemical control. Graze wheatgrasses heavily for a short time in the late
fall or early spring of each year. Wheatgrass pastures that are not fully
utilized by grazing or haying provide egglaying sites, winter protection, and
a habitat that favors black grass bug survival. Mowing and removal of hay may
be a management technique for reducing the number of eggs in some
circumstances.
Black grass bugs will move into wheat planted adjacent to infested areas.
Movement is usually limited to field edges closest to the source of bugs,
with field centers rarely infested. Damage to the wheat appears as a whitish
stippling on leaf sites where bugs have fed. Wheat plants usually are able to
sustain quite a bit of black grass bug feeding without significant loss in
yield. The yield loss to wheat is correlated to the extent of damage to the
flag leaf. Once the flag leaf is damaged, the damage is irreversible. Wheat
that is stressed by moisture, fertility or other pests will be affected more
severely.
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