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Cereal Aphids - Are They a Concern?

Surprisingly even with how cold it has been, cereal aphids have been active in the wheat crop. It is common to find aphids in the wheat crop every year but there are a few fields in the Blenheim area that were close to threshold last week. What could have happened is that the cold weather over the last few weeks was a bit too cold for the predators, parasitoids and pathogens that attack aphids but somewhat okay for the aphids. This week should help turn things around though with the warmer weather but scouting the crop is advised to ensure thresholds are not reached before the crop heads.

Just the mere presence of aphids does not mean a spray is necessary. It does depend on crop stage as to their impact. Prior to heading, the threshold is 12-15 aphids per stem. Once the crop is heading and beyond, the threshold increases to 50 aphids per stem. Look for natural enemies including aphid mummies caused by parasitoids. If there is a lot of activity by the natural enemies, spraying may not be necessary. Scout more then once before making a management decision to help you determine if the aphids are still on the increase or will be kept at bay by the natural enemies so that the crop can head and get you out of the risk period.

Figure 1. Bird Cherry Oat Aphids on Wheat
Photo Credit: J. Obermeyer, Purdue University

Figure 2. Cereal aphid mummies (parasitized by a wasp)
Photo Credit: Manitoba Agriculture, Food and Rural Initiatives