Soybean aphid numbers hit threshold in many areas of Ontario

Soybean aphid numbers are building quickly in several fields in Ontario, and farmers have already had to book an insecticide pass to get ahead of the pest.

In this week’s Wheat Pete’s Word, host Peter Johnson says reports have come in from the Milverton area and Eastern Ontario with aphids at or above threshold.

It has been a few years since soybean aphids have been a major issue, largely because predator and beneficial insect species do a good job of keeping numbers in check. However, this year, numbers in early planted beans are climbing rapidly, which means farmers need to be scouting.

Tracey Baute, field crop entomologist for the Ontario Ministry of Agriculture, Food, and Rural Affairs posted an aphid update in June, warning that a dry year could mean aphids become an issue.

As for control, aphids are best controlled during the R1 to R5 stages of soybeans, when 80 per cent of the plants in the field have at least 250 aphids per plant, and it is apparent that the population is on the increase.  This threshold gives an approximate seven- to 10-day lead-time before the aphids would reach the economic injury level (~600 aphids per plant), where cost of control is equal to yield loss, Baute says.

Often a second spray is necessary when an initial spray is needed early, at R3 or before, says Johnson. This is because available pesticides have killed both aphids and also predators. A new-to-soybean aphid control product, Sefina, gives excellent control of aphids with low impact on beneficials. In an early spray situation, this low impact on beneficials could potentially prevent the need for a second application, but scouting will be key.

Remember when scouting to use the Aphid Advisor app, which takes beneficial population counts into consideration.

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