| | Wheat midge populations in some parts of Alberta are at levels that indicate a need for producers to monitor their fields for wheat midge. This is the most extensive at high enough levels to cause concern back at levels to be of significant risk for wheat producers in Saskatchewan. The 2006 wheat midge Forecast Map indicates that densities of this insect pest have increased compared to previous years.
The annual fall survey for wheat midge has identified a number of areas with high numbers of cocoons in the soil. Following a few years of relatively low populations of the wheat midge, the cooler, moist environmental conditions in 2004 and 2005 have resulted in conditions favourable for resurgence of this agricultural pest.
The Counties of Sturgeon and Lamont have the highest numbers of midge based on the soil samples with a “hotspot” in the county of Lamont. Moderate numbers were also found in the counties of Minuburn and Two Hills and also at a point in Flagstaff county. Other moderate points scattered across the map indicate the midge is present in most of the survey area and scouting should be taking place in much of east central Alberta.
Producers should note that where the midge has become established previously in an area it is unlikely to completely disappear. For example, low lying and moist areas of field are more conducive to midge survival and provide “reservoirs” for this pest even if conditions have not been ideal elsewhere in a field.
Areas of infestation indicated on the forecast map of over 600 wheat midge per square metre may result in significant damage and yield loss. Wheat midge larvae feeding on kernels can affect final yield, grade and grain quality. Severely damaged kernels that are lost during threshing will lower yield whereas moderately-damaged kernels that are harvested will reduce grade. All areas, even those indicating less than 600 midge per square metre, may result in significant crop damage. In areas indicating levels greater than 1200 midge per square metre, wheat producers are advised to include the cost of insecticide application as part of their 2006 budget.
Parasitism of midge larvae by small wasps has been important in keeping wheat midge populations below the economic threshold. Factors that affect parasitism rates are climatic conditions and presence of the host insect in an area. The wasps tend to have better success under warm, dry conditions. The midge density on the forecast map is adjusted for parasitized larvae.
Monitoring wheat fields will be very important during the 2006 growing season when the midge are flying. In all areas where wheat midge is present growers are urged to monitor wheat fields during the susceptible period (emergence of the wheat head from the boot until flowering begins). 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 biological control agents (parasites).
The distribution of wheat midge as illustrated in the 2006 Forecast map is based on cocoons present in soil samples collected in a 2005 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 2006. 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 (310-3276)) during the 2006 growing season.
The wheat midge survey was conducted by AAFRD, Battle River Research Group, Lakeland Applied Research Association, M.D. of Wainwright and County of Vermillion River. Harvey Anderson a private contractor from Saskatchewan analyzed the samples. The survey was funded by Dow AgroSciences Inc.
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