Pictures of Orange Wheat
Blossom Midge Application Recommendations
for LagonR ,LorsbanR
The orange wheat blossom midge is found
around the world
wherever wheat is grown. In recent years, significant damage
to wheat crops has been reported in Alberta,
Dakota and several
regions of British Columbia.
All wheat varieties are currently susceptible to wheat midge
but some are more seriously affected than
others. Although the midge also attacks other
members of the grass family including barley,
couch grass, intermediate wheat grass and
rye, infestations on these plants are usually not serious enough to warrant
The midge may exist at low population
levels for several years before it becomes a significant problem. But if conditions
become favourable, populations can reach epidemic
proportions quickly. Producers often mistake
the symptoms of an infestation and report that
frost or drought has reduced
wheat yields or grain quality.
Crop damage occurs during
the larval stage. After hatching the midge
larva feeds on the developing
wheat kernel, causing it to shrivel, crack and
The damage to the crop is not readily
apparent because there are no visible changes in colour,
size, or shape of the affected wheat head.
Damage can only be detected
by inspecting the developing seed
Damage to wheat kernels will vary within a single head.
A few kernels may be aborted entirely. Others
will not fully develop and
will be so small and light, they will pass
through the combine with the chaff during
harvest. Still others may be only slightly damaged.
Some may not be affected at all.
The loss of individual
kernels will lower yield, whereas damaged
kernels will reduce the grade
of the harvested wheat. Standards
established by the Canadian
Grain Commission limit midge damage
in No. 1 CWRS and No. 2 CWRS to two per cent
and eight per cent respectively before grade
Life Cycle and Identification
Adult - The adult
midge is a very small, fragile orange fly
about half the size of a very small, fragile orange fly about half the size of
a mosquito, approximately 2 - 3 mm long (1/8 inch) (Figure 1). Two black eyes cover much of its
brown head. The midge
has three pairs of legs which are long relative to its body
size. Its wings are oval shaped, transparent
with fine hairs.
Adult midge emerge from
the pupal stage in late June or early July. During
the day, adults
remain within the crop canopy where conditions
are humid. In the evening, females become
active at the top of the wheat canopy, laying their eggs on the newly emerged
heads of wheat. Female midge
lives for less than seven days anddeposit an average of 80 eggs.
- Egg laying takes place after 8:30 p.m. when wind
speeds are less than 10 km/h (6 mph) and
the air temperature is greater than 15o C (59o F). Eggs
are laid singly or in clusters of three or
four eggs on the florets or in grooves on the florets. The egg stage lasts four
to seven days.
- Upon hatching, the small orange larvae (Figure 2) feed
on the surface of developing kernels.
Frequently, there are
larvae per floret but in severe infestations, there may be as many as 26 larvae
feeding on a single kernel.
Larvae feed anddevelop for about two or three weeks, by which
time they grow to about 2 - 3 mm long (1/8 inch).
In dry conditions,
larvae do not shed
their last larval skin but shrink back inside
it and stop developing.
In this state, the larvae appear to be enclosed
within a transparent envelope. The larvae can survive in this protected
state for up to two months. When moisture conditions
improve, the larvae become active, crawl off the wheat heads,
find their way to the ground
and bury themselves in the soil.
Most larvae remain within the top 5 cm (2 inches) of soil but some may
burrow 10 cm (4 inches) below the soil surface. The larvae spin round
cocoons which are about half the size of a polish-type canola seed
(Figure 3). Overwintering
larvae may remain dormant until conditions
are fabourable for development,
whether the following spring or several years later.
- Once temperature and soil
the overwintering period,
the larvae become active and move to the soil
surface to pupate. Depending on the conditions,
the larvae will pupate with or without a cocoon. Adult
flies begin to emerge from the pupae in late June or early July. Emergence may
continue for about six weeks.
Monitoring Careful, close monitoring of the wheat field
is necessary in order
a wheat midge
to take the appropriate action.
Recent studies indicate
that wheat heads are more susceptible to damage
when egg laying occurs during
heading. Kernel damage
is reduced by
20 to 25 fold between heading
and early flowering. Therefore, fields
should be inspecteddaily from the time wheat heads
emerge from the boot leaf until anthers are visible on the heads.
Exception:Glenlea wheat remains
very susceptible to damage after flowering.
Monitor this variety carefully throughtout the heading
and flowering stages.
Field inspections should
be carried out between and when female midge are most
active. Femailes are more active when the temperature
is above 15o C (59o F) and
wind speed is
less than 10 km/h (6 mph).
Midge populations can be estimated
by counting the number of adults present on
four or five wheat heads. One midge
adult for each four or five heads
usually warrants control measures.
Inspect the field in at least three or four
locations. Midge densities
and plant growth stages at the edge
and centre of fields
may be very different. The highest densities
are often next to fields where wheat was grown
in previous years or in low spots where soil moisture is favourable
to midge development.
Don't confuse wheat midge with lauxanids
Not every small fly in the crop will be a wheat midge.
The wheat midge may be mistaken for another
small fly that is common in wheat - the lauxanid (Figure 4).
At 2.5 - 4 mm in length 1/10 - 1/6 inches), the lauxanid is a little larger than the mmidge. It is yellowish-brown in colour
compared to the predominantly
orange colour of the midge.
may be observedduring
the day and
early evening resting on the wheat leaves or on the awns. When disturbedduring the day,
it will fly above the crop canopy. At rest, its body
will be oriented in the horizontal position or
with its head pointed
towards the ground.
In contrast, the midge is not active during
the day. Wheat midge
tends to flutter from plant to plant and
assumes a vertical position with its headpinted
skyward when resting on the plants.
Pest Management Biological, cultural and
chemical controls affect wheat midge
Wheat midge populations are often held
in check by a small, 1 - 2 mm long (1/25 - 1/12 inches) parasitic wasp calledMacroglenespenetrans
(Kirby) (Figure 5). This small wasp emerges
from its pupa about the same time as its host and
lays its eggs inside those of the wheat midge.
The wasp egg and the midge
egg hatch about the smae time and
the tiny wasp grows slowly inside
the midge larva. It remains dormant
within the midge larva over winter.
In the spring, the parasite grows rapidly, destroying
the midge larva. Under
natural conditions, this parasitic wasp
controls about 40 per cent of the over-wintering population of wheat midge
The effectiveness of two additional
parasites - one from Europe and
one from Britich Columbia - is currently being
researched in Saskatchewan.
Meanwhile, in Winnipeg, wheat
varieties resistant to wheat midge are being
examined. If there two research initiatives
are successful, the opportunities for biological and
cultural control of wheat midge will be
Continuous wheat cropping should be avoided
because this practice favours the buildup
of midge populations.
When wheat midge populations are high in the
soil of a particular field, it is best to
switch from wheat and plant crops that are not
susceptible to midge, such as oilseeds
and pulse crops. Cereals crops such as barley,
oats and annual canary grass can also be grown
with little or no risk of damage.
For spring wheat varieties, damage from a
wheat midge infestation can be minimized
by selecting early infestation can be minimized
by selecting early maturing varieties, increasing seeding
rates to two bushels per acre and seeding
as early as possible. By seeding early, the
crop may head and
flowers before peak adult midge
An insecticide application is recommended
if the action threshold has been reached
before the crop has flowered. The timing of
the application will vary with the insecticide.
Consult the specific recommendations for the
product being used.
All insecticides should
be applied in the evening when female midge are most active at the top of the crop canopy. However,
early morning applications may also produce
Application during the advanced
stages of flowering is discouraged
because plants in this growth stage are no longer susceptible to attack and
the insecticide will have a negative impact on
4E andPyrinexR, are registered
for the control of wheat midge in wheat in Canada.
with ground or aerial equipment provides
effective contact control of adults and
some residual control. It does
not control eggs. Application should be made
within 24 hours of reaching the action threshold
- while the adults are still active. If adult
midge persist, a second
application may be required, provided
the crop has not started to flower. LagonR should
not be applied within 21 days
LorsbanR 4E and PyrinexR effectively control both adults and eggs. Because these insecticides
control eggs, they do not have to be applied within 24 hours of having reached
the action threshold as is the case with LagonR. In fact,
application should be delayed up to four days after the recommended action
threshold has been reached to allow the emergence of the maximum number of
wheat heads from the boot.
Application rates for Lorsban andPyrinex are lower for ground
sprayers (830 - 1000 mL/ha or 336 - 405 mL/acre) than for aircraft (1000 mL/ha
or 405 mL/acre). Uniform insecticide
coverage of wheat heads is essential for the
control of eggs. Evening application is recommended
although early morning applications can provide
should not be used
within 60 days of harvest. Do not re-enter the
for at least 48 hours.
Application - Field
sprayers equipped with flat fan (F) nozzles,
oriented at a 45o angle forward,
provide the best coverage. Boom height should
to comply with recommendations of the nozzle
manufacturer. The insecticide should
be applied at 240 - 275 kPa
(35 - 40 psi) in the highest recommended
water volumes. High water volumes (75 - 100 L/ha) provide
better protection than low water volumes (25 - 50 L/ha).
Application - Insecticides should
be applied in the evening using water volumes
of 18.7 - 37.4 L/ha (2.0 - 4.0 U.S.
gal./acre). Coverage and
kernel protection improve with higher water volumes.
This publication has been produced
as a combined effort of the following agencies:
Agriculture andAgri-FoodCanada, Saskatchewan Agriculture & Food,
Manitoba Agriculture, Alberta Agriculture, North Dakota State Agricultural
Extension Service, and Minnesota Extension Services.