Norwest Equity Partners has sold seed treatment company Becker Underwood Inc. for $1.02 billion to German chemical giant BASF in one of the largest deals in the private equity firm's 50-year history.

The cash deal closed last week, Norwest said Wednesday. Most of Becker Underwood will be part of BASF's crop protection unit, with Becker Underwood's animal nutrition segment joining BASF's nutrition and health division.

Minneapolis-based Norwest Equity Partners is the middle-market investment arm of Wells Fargo & Co. and the state's largest private equity firm, managing nearly $5 billion through a series of debt-and-equity funds.

It acquired Becker Underwood in 2004, helping the Ames, Iowa, company quadruple its sales over that period to annual sales of $246 million, partly through eight acquisitions.

"We pushed the R&D and we really worked to grow this company," said Tim DeVries, Norwest Equity Partners' managing general partner.

Becker uses naturally occurring bacteria to enhance the performance of seeds and is probably best known for "Vault HP," a treatment to enhance soybean yields by improving the plant's nitrogen intake.

It has been an active year for Norwest.

The company has invested $300 million in five companies, including Minnesota Rubber & Plastic, and sold three including Becker.

Jennifer Bjorhus • 612-673-4683