A looming “tsunami” of baby boomer retirements could decimate the management ranks and hobble productivity at many corporations unless companies intensify efforts to develop younger talent, according to a new study.

Many executives are aware of the coming “gray drain,” according to the study conducted by Ernest & Young, an accounting company. But not enough of them have taken steps to head off skill shortages and turnover that could hurt the bottom line.

“The demographics are irrefutable and irreversible,” said William Arnone, one of the survey’s authors, “and companies need to plan for it.”

The U.S. Bureau of Labor Statistics predicts that 43 percent of the U.S. labor force will become eligible to retire before 2012.

The skills and institutional knowledge lost when older workers retire won’t be easily replaced, Arnone said. Management shortages already are appearing in some sectors that have experienced a number of early retirements, including utilities and hospital nursing staffs.

Companies able to differentiate themselves as “older worker-friendly” will be poised to reap dividends, he said, while those that don’t face the prospect of “serious financial and productivity issues” as managers scramble to plug staffing holes when experienced employees retire.

Of the human resource managers Ernst & Young surveyed, 43 percent said they needed to do more to train and develop their managers.

A lack of succession planning will hit middle management particularly hard, according to the report.

Arnone and his colleagues urge companies to identify managers eligible to retire in coming years, decide who should replace them and then begin training those individuals.

Because the post-war generation “has defined work as a way to be a winner in the game of life,” he said, boomers have been hesitant to hand over the reins, one expert said, forcing organizations to keep younger workers on the sidelines.