Agriculture and Agri-Food Canada (AAFC) is testing a new aphid app in the field this summer, which should be widely available by next growing season.
The cereal aphid app is the first smartphone app developed by AAFC, says Dr. Tyler Wist, a federal research scientist based in Saskatoon. It will guide cereal growers and agronomists through the scouting and sampling process, Wist says, and tell them whether crops are at a stage that leaves them vulnerable to aphid damage. It will base control recommendations on economic thresholds that will depend on the grower’s comfort level with aphids, though 12 aphids per tiller will be the recommended target. The app will also include photos of the three most common cereal aphid species to help people identify them.
But the app’s most interesting feature is that it will take into account the field’s population of the aphids’ predators, including lady beetles, green lacewing larvae, damselbugs, minute pirate bugs, and parasitoid wasps.
“Having natural enemies of aphids in the fields can prevent the aphid population from reaching a damaging level and the app works to incorporate those natural enemies into the mathematical prediction model,” says Wist.
Wist says the app will recommend people keep sampling until a proper sample size is reached. It will then recommend sampling again soon, recommend people not to worry about aphids, or suggest people consider an insecticide application.
Wist says the idea for the app came out of a project funded by the Pest Management Centre in 2012 and 2013. Researchers surveyed natural aphid enemies in cereal fields so they could incorporate those beneficial insects into the thresholds.
Wist adds they were inspired by a University of Guelph smartphone app, called Aphid Advisor, which looked at soybean aphids and their natural enemies. In 2015, Wist and his AAFC colleague Erl Svendsen received funding from the Pest Management Centre to refine the model that took into account natural predators, and use it in a smartphone app.
Wist says it’s been a test project for how to develop these types of apps within AAFC. Several others were involved in building the app, he says, including Elham Karimi, Kirby Frackleton, and Jackson MacDonald.
Wist and his students will be field-testing the app across multiple platforms this summer. Provincial entomologists Scott Meers, Scott Hartley, and John Gavloski will also be putting the app through its paces, along with agrologists recommended by the provincial agrologists.
Scouting tips in the interim
Farmers and agronomists won’t be able to download the cereal aphid app until next year. In the meantime, Wist has some scouting tips.
“Cereal aphids can be a problem wherever the winds bring them,” says Wist. Farmers and agronomists should start scouting as soon as the crop is starting to head.
“Lately, we’ve been seeing aphids in crops from mid-July with a peak in the first week in August,” says Wist. “That three to four week period is the most critical for aphid surveys.”
When the migratory aphids land in a field, they might be confined to a few hot spots at first. However, once they start feeding and reproducing, they can spread through the field.
The first step is to figure out if aphids have landed in the field. Scouters can use a sweep net in a few spots in the field. If they don’t have a sweep net, they can tap plants over a white tray, to see if any aphids fall onto the tray, Wist says. Wist advises checking a few different areas of the field to try to catch any aphid hotspots.
If farmers or agronomists find aphids, Wist says they’ll want to check more systematically by counting aphids on tillers. The economic threshold is an average of 12 to 15 aphids per tiller.
“This threshold is based on previous research on small cereals grains that indicated that this many aphids per head prior to the soft dough stage would reduce yield enough to warrant the cost of an insecticide application,” says Wist. Once crop is past the soft dough stage, aphids can’t damage yields and there’s no need to control them, he adds.
Wist recommends looking at a total of 100 tillers per field. It’s important to make control decisions based on the average over many tillers, rather than a few tillers that have many aphids, he adds. Agronomists and farmers should randomly select 20 tillers from five areas in the field, avoiding headlands and field margins. The sampled areas should each be separated by about 50 paces, he adds.
Top three cereal aphids
There are several cereal aphid species found in the Western Canadian Prairies. English grain aphids and birdcherry-oat aphids are the most common, and often the most damaging. For example, the English grain aphid’s reproductive rate doubles once it starts feeding on the heads.
Greenbug aphids are sometimes found in Western Canada as well. Wist says they cause additional damage to crops because their saliva is toxic to plants.
It’s not essential to identify different aphid species for most scouting purposes, Wist says. But the app will use slightly different growth rates for each species.
Wist has also discovered that the main parasitoid wasp won’t attack the birdcherry-oat aphid, but loves the English grain aphid. That particular insect makes up 98 per cent of the parasitoids that Wist has found so far. Wist is still monitoring aphids and running experiments in the field to figure out how important that parasitoid is in controlling English grain aphid populations, he adds.