Posted 16 May 2010. Plant Health Progress.
Early Scouting Recommended for Soybean Aphids
Pioneer Hi-Bred experts say cool, wet conditions may foster 2010 outbreaks
Source: Pioneer Press Release. www.pioneer.com
Des Moines, Iowa (April 29, 2010)--It’s difficult to predict when and where soybean aphids may pose a serious threat this season. Therefore, scouting should be a top priority, especially if these economically damaging pests show up in nearby counties, says an expert at Pioneer Hi-Bred, a DuPont business.
“Last year we saw high aphid infestations in late-planted regions and also where the growing season turned relatively cool,” says Paula Davis, Pioneer senior manager for insect and disease traits. “The buildup time for aphid populations typically is late June through July, but last year it occurred later, from July into September in some places. Illinois especially got hit with later flights of aphids.”
Growers who struggled with aphids in the past may need to watch conditions closely to avoid a similar fate. Pioneer provides antibiosis ratings and resistant varieties to help growers prioritize scouting in the most susceptible fields. Varieties without resistant genetics or with below-average antibiosis scores may need to be scouted more intensely. Diligent scouting also helps determine whether spraying will be cost effective.
“Many areas hit by aphids last year were cooler than normal,” Davis says. “We potentially could face that problem again this year depending on weather conditions.”
Pioneer scientists and local entomologists currently are watching for early indicators of aphid population growth, particularly in northern states. Aphids first appeared in the Great Lakes states around 2000. A decade later, the pest spans nearly all soybean-growing areas in the U.S. and Canada. Previously regarded as an every-other-year problem, aphids now jeopardize yields every season. It remains difficult to estimate when, where or how heavy infestations may be this season.
If the weather turns hot during the traditional buildup phase, it may help keep populations at bay, Davis says.
“Aphids do best in the 80- to 85-degree range, which is why the northern Corn Belt can be affected easily during the summer,” Davis says. At first growers may not see much visible damage from aphids, but scouting early and often may prevent an explosive expansion later in the season.
“Watch your fields, especially from late June through July,” she says. “Aphids can increase rapidly if conditions are favorable.”
Davis suggests a multipronged solution to combat aphids. Choose varieties with resistant genes adapted to the specific growing region and apply a treatment such as DuPont™ Asana® XL or Lannate® LV insecticide when needed.
“You still need to scout even if you’ve chosen a resistant variety because, although it may lessen the pressure, fields occasionally still need treatment,” she says.
Growers also must consider the presence of biological predators. In particular, lady beetles are natural enemies to aphids, and they may help keep aphid populations from escalating.
Pioneer experts suggest waiting to treat until the pest reaches the economic threshold, or an average of 250 aphids per plant per field. Growers may find clusters of individually infested plants although surrounding plants may not be affected.
“When aphids reach the threshold of 250 aphids per plant, it’s time to consider management options,” Davis says. “Growers can consult with their Pioneer sales professional or local agronomist to help determine next steps.”
Pioneer researchers continue to look for longer-term solutions to aphids by cultivating varieties with genetic resistance as well as developing varieties with strong antibiosis properties. Antibiosis refers to natural characteristics that discourage aphids from feeding and reproducing, and it provides some general protection from all biotypes. Specific resistant genes may guard against one or two biotypes. Researchers score antibiosis ratings as exceptional (E), above average (AA), average (A) or below average (BA).
“There are several aphid biotypes present today,” Davis says. “With antibiosis, aphids may not find the plant as enticing. Resistant varieties are fairly specific, so Pioneer is working to combine resistant genes to enhance durability across multiple biotypes.”
Pioneer has a designated research team for evaluating aphid antibiosis and improving aphid resistance. The team screens diverse aphid collections across North America to find resistance to various aphid biotypes. Drawing from many sources allows Pioneer to determine the right product for the right acre, or to see which varieties excel in specific soybean-growing areas.