Midge populations may be down, but don’t count them out. In fact, just count them.
That is the message that entomologists are delivering to farmers in areas where the insect pest was a threat last season.
“While there isn’t the threat there was last year, the problem is still out there, especially in some specific areas,” said Scott Hartley of Saskatchewan’s agriculture ministry.
John Gavloski of Manitoba’s provincial department said the oddness of the weather this season may have knocked the midge out of synchronization with the wheat crop, but until spring wheat reaches flowering, the threat won’t be over. He said producers shouldn’t be complacent about the effect orange wheat blossom midge could have on 2009’s cereals.
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Agronomist Mike Grenier of the Canadian Wheat Board said the midge threat should be lower than last year.
“But if you are farming in that Yorkton, Watrous, Saskatoon to Prince Albert area, then you should be taking this pest seriously. And maybe in the Kindersley area west into Alberta, however soil moisture may have an effect on whether midge causes a problem west of Saskatoon.”
Work by Bob Elliot of Agriculture Canada in Saskatoon showed that in areas where less than about 20 millimetres of rain has fallen by the end of May, wheat midge populations are drastically reduced.
Each insect species has optimum growth within a fixed temperature range that is common to the region where they live. Outside those temperatures, development is reduced or suspended. This can take insects like midge out of phase with a vulnerable crop stage.
A specific number of heat units must be accumulated at the right time of the year to support the growth of the insect. Degree days are kept as a running total using a base temperature specific to the insect. The emergence of adult wheat midge from the soil begins at about 700 degree days with peak emergence predicted at about 800 degree days when soil moisture is average.
So far, only in areas of southern Alberta, southwestern Saskatchewan and in the Red River Valley near Emerson, Man., have the degree days reached 625 degree days, a point when midge emergence begins.
Hartley said measuring midge is most effective by observing fields in the evening, after the head of the plant begins to become visible in the boot.
Control thresholds are one adult midge per four to five heads to prevent greater than a 15 percent yield loss and one in eight to prevent a grade loss.
