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2008 Alberta Wheat Midge Forecast | |
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The Alberta wheat midge forecast for 2008 shows a drastic increase in the range and intensity of wheat midge in Alberta. For the first year since Alberta started midge surveys the risk level is very high in large parts of central Alberta. This increase in wheat midge risk has also occurred in Saskatchewan.This forecast agrees with the Canadian Grain Commission harvest unload survey that looks at samples with midge damage noted in the grading.
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The 2007 fall survey sampling was increased to include almost all the counties that have wheat production in central Alberta and along Hi-way 2 as far south as Foothills County (High River). Six (6) new counties (Athabasca, Foothills, Rockyview, Mountainview, Starland and Special Areas 4) were included in the survey this year and 13 counties had the number of samples taken increased for a total of 177 samples. The larval cocoons are washed out of the soil samples and counted, and then dissected to determine if they are parasitized.
The forecast is not intended to take the place of individual field monitoring. Even though the forecast for Alberta shows elevated risk of midge damage over a wide range, populations in individual fields can be highly variable. Producers should plan on monitoring their fields when the midge adults are flying and the wheat is in the susceptible stage. In all areas where wheat midge is present growers are urged to monitor wheat fields during the susceptible period (when the wheat head becomes visible as the boot splits until mid-flowering (anthesis)). Regular field scouting on multiple nights in succession is important in understanding the population in a particular field. Temperature and wind play critical roles in egg-laying of the adult female midge.
An insecticide application is recommended when the crop is heading and adult midge density is one midge per 4-5 heads. To maintain optimum grade, insecticide should be used when adult midge population reaches one per 8-10 heads. Late insecticide applications should be avoided, as it is not cost effective and may adversely affect the parasitic biological control agents.
Parasitism of midge larvae by small wasps has been important in keeping wheat midge populations below the economic threshold. These beneficial wasps tend to have better success under warm, dry conditions. Parasite populations will ultimately rise with increases in the midge populations. The midge density on the forecast map is adjusted for parasitized larvae.
It is important to note that once midge has established in an area it is 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 level populations, however, help sustain a population of natural enemies. Natural enemies have traditionally been very important in managing population levels in Alberta.
The distribution of wheat midge as illustrated in the 2008 Forecast Map is based on cocoons present in soil samples collected in a 2007 fall survey. Although a number of factors influence over-wintering survival of the midge, the survey and map provide a general picture of existing densities and the potential for infestation in 2008. Climatic conditions, mainly temperature and moisture, will ultimately determine the extent and timing of midge emergence during the growing season.
Updates of current conditions and wheat midge emergence will be available through the Ag-Info Centre (310 FARM) during the 2008 growing season.
The wheat midge survey was conducted by Alberta Agriculture and Rural Development with assistance from Lakeland Applied Research Association, Battle River Research Group and the County of Wainwright. Soil samples were processed by Alberta Agriculture and Rural Development. The survey was funded by Alberta Agriculture and Rural Development with support from Dow AgriScience. |
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For more information about the content of this document, contact Scott Meers.
This document is maintained by Shelley Barkley.
This information published to the web on January 24, 2008.
Last Reviewed/Revised on December 15, 2009.
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