Bean leaf beetles and soybean planting date

Considering the enormous bean leaf beetle populations in recent years, many soybean growers are interested in options for managing this pest. Cultural control, such as planting date, could be very useful for managing bean leaf beetle. Studies conducted by Larry Pedigo and Mike Zeiss at Iowa State University (1998-1992) quantified the effects of soybean planting date on bean leaf beetle abundance, soybean pod injury, and soybean yield. Treatments were planted at Ames, Iowa, the first through the last week of May. Bean leaf beetle and soybean developmental stage were determined twice weekly and pod injury and yield were measured at harvest.

Results indicated that soybean planted toward the end of May had fewer bean leaf beetles throughout the season compared with those planted the first week of May. Lower beetle populations resulted in significantly fewer beetle feeding days (a feeding day is one adult feeding for 1 day) during pod development and thereby reduced pod injury for 3 of the 4 years of study. Overall, soybean yield potential was not reduced significantly by later planting in May. However, beetle dispersal from early- to late-planted soybean plots during 1 year caused greater pod injury.

The cultural control tactic of later planting resulted in fewer beetles, less pod injury, and similar yields. One risk, though, was that the beetles moving out of earlier maturing fields into later planted soybean could cause late-season damage. Therefore, scouting during pod stages is still necessary, regardless of when soybean is planted.

This article originally appeared on page 51 of the IC-490 (6) -- April 28, 2003 issue.

Updated 04/27/2003 - 1:00pm