Paula Davis, Pioneer senior manager for insect and disease traits, says she expects higher aphid populations in 2011 than in the 2010 growing season, but environmental conditions in the coming weeks will be key to determine the extent. Growers should plan on scouting in late June through mid-August.
Although soybean aphids are a threat every year, outbreaks tend to be on a two-year cycle, Davis says.
"Overwintering populations, natural enemies and environmental conditions are the main factors that impact outbreaks," she says. "However, during an outbreak, late-planted fields can be at higher risk. I think it's too soon to tell what 2011 will bring, but scattered outbreaks are likely. The weather in the next few weeks could really enhance or reduce the risk. With cool conditions, aphids could be a problem. Aphids don't like it really hot."
Long-range forecasts, such as the USDA 90-day outlook, suggest weather temperatures may be cooler than average across the upper Midwest from May to July.
"The optimum temperature for aphid reproduction ranges from 68° to 82° F," says Eric Zumbach, Pioneer area agronomist based in Marion, IA. "If the weather stays in this optimum temperature range, and aphids are present, then it's important to intensify the scouting regimen. If temperatures exceed 90° F, aphid reproduction slows down, which helps keep populations at bay. If growers find 250 aphids/plant, it's time to pull the trigger with spraying.
"If growers are concerned about aphids, they should sample 10-20 plants in 10 different areas of the field," Zumbach says. "The more samples, the better to see what kind of pressure exists in the field. Also look for other signs such as ants or colonies of ladybugs in the field as they both feed on aphids."
Pioneer experts suggest growers leverage antixenosis/antibiosis ratings and select soybean varieties with native tolerance as the first line of defense. Antixenosis and antibiosis refer to natural characteristics that discourage aphids from feeding and reproducing, respectively, and these varieties provide some general protection from all aphid biotypes. Aphid ratings range from exceptional (E) and above average (AA) to average (A) and below average (BA).
Antixenosis and antibiosis evaluations also can help growers prioritize scouting. If an aphid outbreak occurs, growers can concentrate on fields with below-average ratings and save above-average fields for later in the process. This approach continues to be one of the best defenses against aphid damage.
Zumbach says this type of prioritization strategy helps growers who have many acres to cover. He adds that growers can call on Pioneer sales professionals to help determine which varieties to scout first. If growers encounter aphids, it may be necessary to apply insecticide.
While Pioneer researchers continue to look for improved ways to fight soybean aphids, including the development of resistant varieties, growers should continue to be proactive in their aphid management approach.