Assessing whether or not to spray soybean aphids?

There’s an app for that, but farmers still need to scout and take beneficial insects that prey on soybean aphids into account

Uncertain about applying an insecticide to control soybean aphids?

There’s an app for that.

It’s called the Aphid Advisor and it not only takes into account the soybean aphid population, but the population of six main insects that prey on soybean aphids.

“Instead of having a fixed, economic threshold like we are used to having for pests, what we now have is what is called a dynamic action threshold,” Jordan Bannerman, an entomology instructor with the University of Manitoba, said in an interview July 11 on the sidelines of this year’s Crop Diagnostic School hosted by Manitoba Agriculture and the University of Manitoba at its research station here. “The dynamic action threshold… is available in an app that has you enter not only counts of soybean aphids but also the predators of soybean aphids and you use both sets of information to decide whether or not to spray, or to wait, or not spray.”

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The app — a joint effort by the University of Guelph and Ontario Ministry of Agriculture, Food and Rural Affairs — is available for Apple’s iPhone and iPad and BlackBerry smartphones. (Go to www.aphidapp.com to get the app, which won’t come up when you search Apple’s App Store.)

The economic threshold for spraying soybean aphids has been an average of 250 per plant and rising, but that number is probably too low if the field also has a good population of insects that attack soybean aphids, Bannerman said.

“What this new tool does through this app is says if you have 300 aphids per plant and you also have one lady beetle… per five plants, you may not actually be above the threshold because we know that predator is going to help reduce the population so you wouldn’t necessarily have to spray,” he said.

There are two main steps when using the app, Bannerman said. One is getting a good representative sampling of the soybean aphid population. The second is doing the same for the main six insects that prey on them. The app has photographs of each of those predatory and parasitic insects.

“So even if an agronomist or grower is not very familiar with these (beneficial insects) photos help a lot because you can actually use this right in the field to help make sure that you are accurately identifying the predators and parasites that you need to effectively use this tool,” Bannerman said.

Manitoba Agriculture extension entomologist John Gavloski, who worked with Bannerman at the diagnostic school, discussed the main insects that attack soybean aphids. They are:

Lady beetles (adult and larvae)

Everyone knows what an adult lady beetle looks like. And most know they eat aphids. But juvenile lady beetles also eat soybean aphids.

“The juvenile lady beetles look like miniature black alligators,” Gavloski said in an interview. “(T)hey can individually eat about 100 soybean aphids per day per individual. They are very good predators.”

Seven spotted lady beetle larva.
photo: John Gavloski, Manitoba Agriculture

Lacewings (adult and larvae)

“Lacewings as adults are fairly large green insects with lacy wings as the name would indicate,” Gavloski said. “Their larva look like miniature brown alligators.

“They are also fairly aggressive aphid consumers.”

Lacewing larva eating lygus bug.
photo: John Gavloski, Manitoba Agriculture

Hover fly (Syrphid larvae)

Adults look a lot like bees or wasps, but have no stinger and can hover.

In the juvenile stage hover flies are slug-like and brown, green or sometimes pale in colour. Hover fly larvae use their hook-shaped mouth to impale aphids and suck their fluid out, killing them.

Hover fly larvae.
photo: John Gavloski, Manitoba Agriculture

Minute pirate bugs (Orius), (adults and nymphs)

Theses are very tiny insects with black and white patches. They appear early in soybean fields and initially may feed on pollen and plant sap, but they don’t cause economic damage to the soybeans, Gavloski said.

“When suitable prey such as soybean aphids arrive they are there waiting for them,” he said. They’re another highly beneficial insect.”

Minute Pirate Bug.
photo: John Gavloski, Manitoba Agriculture

Aphidoletes

This is a small midge fly whose larvae feed on aphids. The yellowish to orange larvae are small too — only a couple of millimetres long.

“They are small and legless but they can squirm around pretty good and can get themselves into an aphid colony and start devouring the aphids,” Gavloski said. The slug-like larvae inject a toxin into aphids’ leg joints to paralyze them and then suck out the aphid body contents through a hole bitten in the thorax. Larvae can consume aphids much larger than themselves and may kill many more aphids than they eat when aphid populations are high.

Aphid Mummies

‘Mummies’ (see photo at top of page) are caused by parasitic wasps that lay their eggs in aphids resulting in the aphid’s death as the eggs hatch and transform into larvae, Gavloski said.

“Eventually the soybean aphids become inflated and brown or black, depending on the species of wasp that is parasitizing the aphid,” he said. “They look kind of bloated and they change colour and eventually you will have a hole in the end of the aphid where the wasp popped out after it developed.”

Mummies need to be included in the count of natural enemies present in the soybean field when using the Aphid Advisor app.

About the author

Reporter

Allan Dawson

Allan Dawson is a reporter with the Manitoba Co-operator based near Miami, Man. Covering agriculture since 1980, Dawson has spent most of his career with the Co-operator except for several years with Farmers’ Independent Weekly and before that a Morden-Winkler area radio station.

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