- Created: Thursday, 03 July 2014 19:29
|Virulence and Seed Technologies7
Certain wheat varieties have an Sm1 gene which are resistant to wheat midge.
This provides a 14.8% yield advantage over non-resistant varieties.8
A small proportion of wheat midge are unaffected by the Sm1 gene and are considered virulent. Thus, growing only resistant varieties would cause virulent midge selection, compromising Sm1 gene resistance.
Therefore, 10% of a seed lot needs to be non-resistant to act as a refuge.
An evenly spaced refuge variety allows susceptible midge to survive and mate with virulent midge, keeping the virulent midge population from becoming dominant (non-virulence is the dominant trait).
A Midge Tolerant Wheat Stewardship Agreement must be signed to be able to grow midge tolerant varieties which states: farmers cannot use the seed past certified seed more than one generation to ensure there is enough refuge seed within the tolerant seed so that virulent midge strains do not reach high levels
- Emerge from pupal stage in late June – early July with 50% emerging after 784 DD (+/-2.5 days)3 accumulated with males emerging a few days before females.
- Usually begin laying eggs on second day of emergence.
- Females lay an average of 80 eggs over their 7 day lifespan.
- Eggs usually laid after 8pm, when wind is <10km/h, and temperature >15°C.4
- Laid either on florets, within grooves of florets, or on external surface of glumes.1
- Usually laid in clusters of 3-4 eggs.2
- Hatch after 4-7 days depending on environmental conditions; especially temperature and move from outer surface of wheat head inward to feed upon developing wheat kernels.
- Larvae develop into 3 instars over 2-3 weeks growing 2-3mm in length.
- Upon growth completion, larvae drop and bury to 5 cm in soil, forming a protective cocoon to overwinter.
- With adequate moisture and temperature, larvae move to near soil surface to pupate, but may exist for two years in soil if conditions poor.
Insecticide application recommended when there is one adult midge for every 4-5 wheat heads, which would reduce yields 15%. Evening application recommended, when wheat midge is most active.
Application during advanced stages of flowering is discouraged, since the larvae inside wheat florets are unlikely to be affected, and the wheat is not susceptible to additional attack.
Insecticides containing chloropyrifos or dimethoate are registered for wheat midge control in Canada.
Dimethoate affects only wheat midge adults.
Should be applied within 24 hours of reaching the action threshold.
Chloropyrifos affects adults and eggs.
Application should be delayed up to and no more than 4 days after action threshold in order to maximize the number of emerged wheat heads.
Uniform insecticide coverage of wheat heads is essential for egg control.
Insecticides can have a negative effect on wheat midge parasites.
Can be dangerous: wheat fields should not be re-entered for at least 48 hours upon the spraying of Chloropyrifos.
Midge monitoring is occurring during anthesis throughout Alberta. Many of our local producers have agreed to assist in this by hosting traps on their land and monitoring these traps daily. This information will be processed daily and posted.
The wheat midge forecast for 2016 indicates a general decrease for midge risk. Individual fields throughout Alberta may still have economic levels of midge. Each producer also needs to assess their risk based on indicators specific to their farm.
This forecast is not intended to take the place of individual field monitoring. The forecast for Alberta shows areas of risk for midge damage in 2016. It is important to note that over such a wide range, populations in individual fields can be and often are highly variable. Producers should plan to monitor their fields when the midge adults are flying and their wheat is in the susceptible stage. In all areas of the province growers are urged to monitor their wheat fields from wheat head emergence to anthesis (the susceptible stage) for the presence of midge adults. Regular field scouting on multiple nights in succession is important in understanding the population in a particular field.
Although a number of factors influence the overwintering survival of the midge, the survey and map provide a general picture of existing densities and the potential for infestation in 2016. Weather conditions, specifically temperature and moisture will ultimately determine the extent and timing of midge emergence during the growing season. Temperature and wind also play critical roles in egg laying activities of the adult female wheat midge. The level of damage from wheat midge is determined by the synchrony of wheat midge emergence and wheat coupled with the number of wheat midge. Parasitism of midge larvae by a small wasp species (Macroglens penetrans) has been important in keeping wheat midge populations below the economic threshold in many areas. These beneficial wasps tend to thrive in warm, dry conditions. Parasite populations increase and decrease with changes in the midge population and are very important in moderating population levels in Alberta.
It is important to understand that once midge has established in an area it unlikely to ever completely disappear. Low lying and moist areas in a field provide a refuge, enabling the population to survive even when conditions are not favorable in the rest of the field. These low population levels, however, also help sustain a population of natural enemies.
- Wheat Midge Agdex 2507
Information all producers should know about the Orange Blossom Wheat Midge. This article includes some cool photos, life cycle and identification, monitoring, pest management and cultural control.
Produced as a combined effort of :
- Alberta Agriculture, Food and Rural Development
- Saskatchewan Agriculture and Food
- Manitoba Agriculture and Food
- British Columbia Agriculture and Food
- Agriculture and Agri-=Food Canada
Images courtesy of Saskatchewan Agriculture and Food
- Midge Tolerant Wheat
This site is an excellent source of information on Midge tolerant wheat varieties. It explains the refuge system and how fragile this protection is. It also explains why it is important to follow the rules for seeding the midge tolerant varietal blends.
The Midge Tolerant Wheat Stewardship Team is a broad industry coalition representing plant breeders, government, seed growers, seed distributor and producer groups. The team is committed to maintaining the viability of midge tolerant wheat by educating Canadian wheat producers on the importance of proper stewardship of the technology.
- Canadian Grain Commission Official Grain Grading Guide Section 4-19
This section deals with midge damaged kernels and grain grading.
- Integrated pest management of the Wheat midge in North Dakota
Another source of information on host plants, identification, life cycle, damage, identifying fields at risk, degree days as a tool for scouting, monitoring in the field, economic thresholds, methods of detecting wheat midge in the fields, integrated pest management and resistant varieties.
- Other Wheat Midge Information
Prairie Soils and Crops Journal Management Practices for Wheat Midge