Wheat Midge
Damage
| Life Cycle and Identification
| Monitoring
| Pest Management
Some provinces and states conduct annual surveys for wheat midge to determine midge
distributions and to warn producers of possible outbreaks. Consult your
local extension office for details in your area.
The wheat midge (Sitodiplosis mosellana) is found in most areas around the world
wherever wheat is grown. In recent years, significant damage to wheat
crops has been reported in Alberta, Saskatchewan, Manitoba, southern
British Columbia, Minnesota, North Dakota and Idaho.
Figure 1. Side view of the wheat midge resting on wheat
spikelets. Photo courtesy Saskatchewan Agriculture and Food. |
![wheat midge](/web/20061229053506im_/http://www.agf.gov.bc.ca/cropprot/images/midge1.jpg) |
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 control. Research and breeding for wheat midge resistant wheat
varieties is underway at the Cereals Research Centre (A.A.F.C. - Winnipeg)
and the Crop Development Centre (University of Saskatchewan).
Damage
Infestations of
wheat midge can reduce crop yields and lower the grade of the harvested
grain.
Midge may exist at low
population levels for several years before they become a significant
problem. But, if conditions become favourable, populations can reach
epidemic proportions quickly. Producers inexperienced with wheat midge
infestations often mistake the symptoms of damage and report that frost or
drought was responsible for reduced wheat yields or grain quality.
Crop damage occurs
during the larval stage. After hatching, the midge larvae feed on the
developing wheat kernel, causing it to shrivel, crack and become deformed.
As there are no visible, external changes in colour, size or shape of the
affected wheat head, the damage to the crop is not readily apparent.
Damage can only be detected by inspecting the developing seed within the
glumes.
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 kernels may not be affected at
all.
The loss of kernels
lowers the yield, whereas damaged kernels reduces 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 2% and 8% respectively,
before grade is affected. Damage tolerances for amber durum are 2% for No.
1 CWAD and 8% for No. 2 CWAD. However, if there is disease
associated with midge damage, referred to as severe midge damage, grading
tolerances are only 0.1% and 0.25% for CWAD No. 1 and No. 2
respectively. More detailed information regarding grading is
available at the Canadian Grain Commission web site. (http://www.cgc.ca/ in Chapter 4 – Wheat,
of the Official Grain Grading Guide)
Life Cycle and Identification
The life cycle of the wheat midge has four stages.
ADULT - The adult midge is a very small,
fragile orange fly about half the size of a mosquito, approximately 2- 3
mm long. Two black eyes cover much of its head. The midge has three pairs
of legs that are long relative to its body size. Its wings are oval
shaped, transparent and fringed 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 eggs on the newly
emerged wheat heads. Female midge, who live for less than seven days, lay
an average of 80 eggs.
EGGS -
Egg laying generally takes place after 8:30 p.m. when wind speeds are less
than 10 km/h and the air temperature is greater than 15°C. Eggs are laid,
either singly or in clusters of three or four eggs, on the florets, on the
external surface of the glumes or in outer grooves on the florets. The egg
stage lasts four to seven days, depending on environmental conditions,
especially temperature.
Figure 2. Wheat midge larvae feeding on developing wheat
kernel. Photos courtesy Saskatchewan Agriculture and Food. |
![wheat midge larvae](/web/20061229053506im_/http://www.agf.gov.bc.ca/cropprot/images/midge0106a.jpg) |
Early stage of kernel development |
![wheat midge mature larvae](/web/20061229053506im_/http://www.agf.gov.bc.ca/cropprot/images/midge0106b.jpg) |
Mature larvae – kernel severely damaged |
LARVAE –
Upon hatching, the small orange larvae move from the outer surface into
the head to feed on the surface of developing kernels (Figure 2.).
Frequently, three to four larvae per floret have been observed, but in
severe infestations, there may be as many as 26 larvae feeding on a single
kernel.
Figure 3. Canola seeds (left) and wheat midge cocoons
(right). Photo courtesy Saskatchewan Agriculture and Food. |
![wheat midge cocoons](/web/20061229053506im_/http://www.agf.gov.bc.ca/cropprot/images/midge0106c.jpg) |
Larvae feed and
develop for two to three weeks, growing to 2 to 3 mm in length, before
crawling off the wheat head to find their way to the ground and bury
themselves in the soil. Under dry conditions, larvae will remain in the
head and, rather than shedding their last larval skin, will shrink back
inside the skin and stop developing. The larvae appear to be enclosed
within a transparent envelope and can survive for some time in this
protected state. The larvae will become active when moisture conditions
improve and may move into the soil. However, the larvae may also remain in
the wheat heads until threshed out during harvest.
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 that are about half the size
of a Polish-type canola seed. (Figure 3) Over-wintering larvae may
remain dormant until conditions are favourable for development, whether
that is the following spring or several years later.
Figure 4. Wheat midge pupae. Photo courtesy Saskatchewan Agriculture and Food. |
![wheat midge pupae](/web/20061229053506im_/http://www.agf.gov.bc.ca/cropprot/images/midge0106d.jpg) |
Actual size 2
to 3 mm |
PUPAE –
Once temperature and soil conditions end the over-wintering 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.
Temperature, soil moisture and geographic location will affect emergence
of the adult flies, which commences in late June or early July. Emergence
can continue for up to six weeks.
Monitoring
Careful, regular
monitoring of wheat fields between heading and flowering is necessary in
order to identify a wheat midge infestation and to take the appropriate
action.
Research indicates
that wheat heads are most susceptible to damage when egg laying occurs
during heading. (Figure 5.) Kernel damage due to wheat midge, declines by
15 to 25 fold between later stages of heading and early flowering or
anthesis (first yellow anthers appear on wheat head). Therefore, fields
should be inspected daily 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 throughout anthesis. Monitor this variety carefully throughout the
heading and flowering stages.
Field inspection
should be carried out after 8:30 p.m. when the female midge are most
active. Females are more active when the temperature is above 15°C (59°F)
and wind speed is less than 10 km/h (6 mph). When wind speeds are greater
than 10 km/h egg-laying may still occur on shorter, tillering heads within
the shelter of the crop canopy. Midge populations can be estimated by
counting the number of adults present on four or five wheat
heads.
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.
Often midge infestations are higher at field edges with populations
declining dramatically toward inner parts of the same field. In these
situations control around the field margins may provide adequate control
and result in reduced cost. However if midge densities remain relatively
constant at all sampling sites control over the entire field is warranted.
Figure 5. Growth stages of Wheat. |
![growth stages of wheat](/web/20061229053506im_/http://www.agf.gov.bc.ca/cropprot/images/midge0106e.jpg) |
Don’t confuse wheat midge with lauxanids
Figure 6. Lauxanid, Camptoprosopella borealis (left) and
wheat midge (right). Photo courtesy Saskatchewan Agriculture and Food. |
![wheat midge](/web/20061229053506im_/http://www.agf.gov.bc.ca/cropprot/images/midge0106f.jpg) |
Not every small fly in
the crop will be a wheat midge. The wheat midge may be mistaken for
lauxanid, another small fly that is common in wheat.
At 2.5-4 mm in length
(1/10-1/6 inches), the lauxanid is a little larger than the midge. It is
yellowish-brown in colour compared to the predominantly orange colour of
the midge.
The lauxanid may be
observed during the day and early evening resting on the wheat leaves or
on the awns. When disturbed during 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
usually not active during the day. Wheat midge tends to flutter from plant
to plant and assumes a vertical position with its head pointed skyward
when resting on the plants.
Characteristics |
Lauxanid |
Wheat Midge |
Size |
2.5 - 4 mm
(1/10-1/6 inches) |
2 - 3 mm (1/12 -
1/8 in.) |
Colour |
yellowish-brown |
orange, brown
head, black eyes |
Active
period |
day and
evening |
primarily
evening |
Movement
habits |
will fly above
the canopy when disturbed during day |
tends to flutter
from plant to plant in the evening |
Stationary
habits |
sits on plant in
horizontal position or pointing down |
sits with head
pointing up |
Pest Management
Biological, cultural and chemical controls affect wheat midge
populations.
BIOLOGICAL CONTROL
Figure 7. Female (with midge eggs). Photo courtesy Saskatchewan Agriculture and Food. |
![female (with midge eggs)](/web/20061229053506im_/http://www.agf.gov.bc.ca/cropprot/images/midge0106g.jpg) |
On the prairies, wheat
midge populations are often held in check by a small, 1 - 2 mm (1/25 -
1/12 inches) long parasitic wasp called Macroglenes penetrans
(Kirby) (Figure 7). In southern B.C. another small parasitic wasp,
Euxestonotus error (Fitch) attacks the wheat midge similar to M.
penetrans.
The 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
same time and the tiny wasp grows slowly inside the midge larva.
Parasitized midge
larvae are still capable of damage to the crop during the current season.
Itremains dormant within the midge larva over winter. In the following
spring, the parasite grows rapidly, destroying the midge
larva.
It is important to
remember that benefits from parasitism will not be realized until the
following year. Therefore, while wheat is susceptible to damage,
control measures should be considered in the current year if midge
populations exceed the economic threshold.
Estimates of parasite
activity, from samples collected for the annual wheat midge surveys
conducted in Saskatchewan, have indicated parasitism rates ranging from 0
to 100% in the province. Generally the highest percentages of parasitism
occur in areas midge populations have been established for a few years.
Conversely, the lowest rates of parasitism are usually seen in areas new
to the wheat midge, but where the parasite has not yet become
established.
CULTURAL CONTROL
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 to 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.
Seeding Dates
Research trials with
early and later seeding dates have had variable results in reducing midge
damage, depending on variety and wheat classes. Tests with traditional
spring wheat varieties showed that early seeding of early maturing
varieties resulted in greatly reduced midge damage. These early maturing
varieties tended to grow through the susceptible stage before the wheat
midge emerged from the soil. However, recent tests with newer spring
wheat, CPS and durum varieties showed late seeding resulted in the least
amount of damage from the midge. This appears to be related to the fact
that the new, higher yielding spring wheat, CPS and durum varieties head
out over a longer period of time and therefore remain susceptible
longer.
For these varieties,
the susceptible stage and midge presence in the field coincided, so early
seeding does not appear to be a viable, non-chemical control option.
Another complicating
factor in the more recent trials is that the testing was done during “el
Nino” years with rather unique environmental conditions. Further testing
will be required before any reliable recommendations can be made. Early
seeding of early maturing spring wheat varieties may still be a useful
method for non-chemical management of midge populations.
Soil type was another
variable identified when considering seeding dates in cultural
control. Days to heading was, on average, five to six days longer on
heavy textured soil than on light-textured soil, therefore extending the
period of time that the wheat was susceptible to midge damage. More
detailed information is available at the Agriculture and Agri-Food Canada
website. (Research Letters at http://res2.agr.ca/saskatoon/)
CHEMICAL CONTROL
Action or Economic Threshold
Yield considerations
- An insecticide application is recommended when there is at least one
adult midge for every four or five wheat heads. At this level of
infestation, wheat yields will be reduced by approximately 15 per cent if
the midge is not controlled. Higher midge densities will reduce yields
even further.
Grade considerations
– The Canadian Grain Commission’s changes to grading tolerances have
prompted re-evaluation of the economic threshold for wheat midge to
maintain optimum grades. In areas where growing conditions are
favourable to the production of No. 1 grade wheat, chemical control may be
required when midge populations reach one adult midge for every eight to
ten wheat heads during the susceptible stage.
Cygon®, Lagon®, Lorsban® 4E, Nufos® and Pyrinex®, are registered for the
control of wheat midge in wheat in Canada. 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
being used. 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 acceptable results.
NOTE:
Application during the advanced stages of flowering is discouraged because
plants in this growth stage are no longer susceptible to attack and any
larvae already inside the florets are unlikely to be affected by an
insecticide. The insecticide will have a negative impact on midge
parasites.
Cygon® and Lagon® applied with ground or aerial equipment provides 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.
Lorsban® 4E, Nufos® and Pyrinex® control 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 Cygon® and Lagon®. In fact,
application should be delayed up to four days after the recommended action
threshold has been reached. This strategy allows a maximum number of wheat
heads to emerge, resulting in increased protection.
Only one application of Lorsban® 4E, Nufos® and Pyrinex® is allowed per
season.
Application rates for
Lorsban® 4E, Nufos® and Pyrinex® are lower for ground sprayers (336-405
rnL/acre) than for aircraft (405 mL/acre). Uniform insecticide coverage
of wheat heads is essential for the control of eggs. Evening
application is recommended although early morning applications may provide
acceptable control.
Lorsban® 4E, Nufos®
and Pyrinex® should not be used within 60 days of harvest. Do not re-enter
the treated field for at least 48 hours.
Application Recommendations |
General -
Evening applications are recommended, although early morning may
produce acceptable results. |
Cygon®
and Lagon® (dimethoate) |
Apply within 24
hours of reaching the action threshold A second application may
be necessary Do not apply within 21 days of
harvest |
Lorsban® 4E,
Nufos® and Pyrinex® (chlorpyrifos) |
Delay
application up to four days after reaching the action threshold to
allow more wheat to head out, resulting in coverage of an increased
number of heads Do not apply Lorsban within 60 days of
harvest Do not re-enter treated field for at least 48
hours |
Ground application - Field sprayers equipped with flat fan (F) nozzles,
oriented at a 45º angle forward, provide the best coverage. Boom height
should be adjusted 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 -
100L/ha) provide better protection than low water volumes (25- 50 L/ha).
Aerial application - Insecticides should be applied in the evening using
water volumes of 18.7- 37.4 L/ha. Coverage and kernel protection improve
with higher water volumes.
New sprayer technology (e.g. air-assisted, Venturi® nozzles) in application of insecticides for control of wheat midge has not been adequately researched to determine
efficacy with lower water volumes.
This publication has
been produced as a combined effort of the following agencies:
Saskatchewan Agriculture and Food
Agriculture and Agri-Food Canada
Manitoba Agriculture and Food
Alberta Agriculture, Food and Rural Development
British Columbia Ministry of Agriculture, Food and Fisheries
Return to Publications Page
Return to Crop Protection Program
|