New soybean variety offers aphid resistance

Saturday, September 20, 2008

by SUSAN MANN

Soybeans have been grown on Dave Ferguson’s farm in Lambton Country for 35 years by both himself and his father but it was only six-to-seven years ago that aphids showed up in the crop.

At that time no one really sprayed insecticides to control them except on test strips. “They devastated the soybean crop,” he recalls. “We lost 10 to 15 bushels an acre.”

Since then they’ve had to spray once or twice during the past few years. “We learned very quickly that it’s economically feasible to spray when you get that critical mass,” he says. Today his controls involve monitoring fields for aphids and only spraying when they’ve reached threshold levels.

Starting in November soybean growers will have a new option to control aphids. That’s when Syngenta Seeds Canada Inc. launches its new integrated management system for aphid control. It includes a seed with built in aphid resistance, the seed is treated with an insecticide that lasts the first 60 days after planting, and finally there’s the continued need for regular field monitoring and spraying if threshold levels are reached.

“The whole system’s developed to work with the biological controls that are out there now, which are the ladybugs and the natural predators of the aphid,” explains Syngenta crop manager David Townsend.

The seed treatment is the first line of defense, while the seed with build in resistance offers protection for the whole growing season. The seed itself and the seed treatment do not affect the beneficial insects, notes Townsend.

The benefit of Syngenta’s new system is it works much earlier than just using sprays. “This system works so much earlier that we think it’s a better system,” he says. “It holds them (aphids) back enough for the beneficials to really help out.”

About yields, Townsend says the seed with built in aphid resistance doesn’t have any yield reduction compared to seeds without the resistance. “When we tested it in the field there doesn’t appear to be any yield difference”

That’s important to farmers like Ferguson. He sees Syngenta’s system as another tool in farmers’ tool chests. It may mean one less trip with the sprayer, which may save money. But he believes yield is king. “I won’t try a soybean variety only because it has aphid resistance. It still has to show me top yield.”  

Aphids were quite low in numbers this year mainly because the abundant rain enabled natural enemies and fungus that controls them to keep up, says Tracey Baute, field crop entomologist with OMAFRA. In fact, weather conditions were ideal for the beans to get big and healthy.

This year’s low aphid numbers was surprising, she says. “I think it would have been different had the weather been a bit different because aphids were definitely here and able to try and colonize.”

In previous years there have been fairly substantial infestations in certain areas of Ontario every year. In some years the infestations have been fairly widespread across Ontario, while in other years there are hotspots.

Any area where there are buckthorn shrubs, from West Lorne to Quebec, is more at risk. Aphids are a concern, she explains, because they can spend the winter in the province on buckthorn shrubs in addition to being carried in from the Untied States.

Aphids damage bean plants by sucking out nutrients. If the plants are stressed by drought or disease they then don’t have enough energy to put into the seeds in the pods so they’ll be as big as they could be or to put enough seeds into the pod. On average it can cause a 10-bushel-per-acre loss in yield.

“It certainly can have quite a substantial impact,” she says. But that impact has been mitigated by the development of thresholds. “We do know when to go in and spray. That has reduced the impact the aphid has had on the crop.”

Farmers have to routinely scout their fields to stay ahead of the situation and respond before there’s significant damage. The threshold is 250 aphids per plant on 80 per cent of the plants in the field. Growers should also be looking to see if those populations are increasing past threshold levels.

Monitoring fields regularly for increases in aphid populations is important, Baute says, because natural enemies can keep them below threshold levels. But sprays can kill off natural enemies that help keep aphids down. BF