DES MOINES -- Growers now have a new tool in their arsenal to manage soybean aphids.

Soybean breeders with Pioneer Hi-Bred International Inc. have rated Pioneer(R)-brand soybean varieties for their natural ability to ward off soybean aphids by reducing their life span or inhibiting reproduction. This offers growers better information to prioritize field scouting and, if needed, aphid insecticide spraying.

Certain soybeans can naturally reduce the rate of growth, survival and reproduction of aphids feeding on soybean plants. This type of resistance is called "antibiosis." Pioneer has developed a screening technique for aphid antibiosis in collaboration with Kansas State University and now is making these ratings available to growers.

"Since 2000, when aphids were first found in the United States, this insect has been a costly pest for soybean growers," said Leon Streit, Pioneer soybean breeder. "These ratings give growers a leg up. When used as a management tool, they can help growers determine when to scout and when to spray."

Growers benefit from ratings

Streit notes that by knowing a variety's rating, growers can more efficiently scout soybean fields for aphids. Pioneer soybean varieties are given one of the following designations for soybean aphid management -- exceptional, above average, average or below average.

"Based on ratings, growers first can scout fields planted to varieties with a below-average rating and with greater frequency than fields planted to varieties with average, above-average or exceptional scores," he said.

"According to our screening and characterization studies, aphids will reproduce faster on varieties rated as average or below average than on varieties with exceptional or above-average ratings," said Streit. "It's important to note these ratings are relative comparisons.

"Varieties with an exceptional antibiosis rating can come under attack or be damaged by soybean aphids. It's just that varieties with exceptional ratings display much lower aphid reproduction than those with average or below-average ratings."

Streit says soybean researchers are not certain as to the mechanism that causes aphid resistance. Insects pull nutrients from the phloem tube of a plant, which may play a part in resistance. The location and accessibility of the phloem tube or the taste of the sap may keep aphids at bay.

Soybean aphids have needlelike sucking mouthparts, which they insert into soybean tissues to remove plant sap. If aphid numbers are high, leaves may become yellow and distorted, the plant may become stunted and plant parts may be covered with a dark, sooty mold. Yield losses often accompany these symptoms.

Soybean aphid antibiosis ratings are available on Pioneer soybean varieties sold for 2006 planting. For information on these aphid antibiosis ratings, contact your local Pioneer sales professional.

Pioneer researchers are focusing on identifying exceptional sources of antibiosis and incorporating this trait into an increasing number of Pioneer varieties in the upcoming years.

Pioneer Hi-Bred International Inc., a subsidiary of DuPont, is the world's leading source of customized solutions for farmers, livestock producers and grain and oilseed processors. With headquarters in Des Moines, Iowa, Pioneer provides access to advanced plant genetics, crop protection solutions and quality crop systems to customers in nearly 70 countries.

SOURCE: Pioneer Hi-Bred International.