The bean leaf beetle has been a major concern this spring, most notably in early-emerging fields where their numbers reached economic thresholds or in areas where the bean pod mottle virus caused problems last year with green stem. In both of these situations I received reports of insecticides being used to prevent economic damage from the beetles.
It appears that winter survival of the bean leaf beetle was fairly good in some areas, probably because of the continuous snow cover that lasted more than 100 days across northern and central Iowa. The overwintered beetle population in central Iowa is now on the decline and this is good news for farmers with late-emerging soybean fields. I would not expect any field with soybean plants emerging after mid-June to have overwintered beetles reach the economic threshold. Another benefit of later emerging soybean is that the populations of both the first generation (July) and the second generation (August and September) are often relatively small and usually do not cause economic damage, especially to the pods. However, fields still should be scouted in late summer for bean leaf beetle pod injury regardless of the soybean emergence date.
This article originally appeared on page 122 of the IC-486(15) -- June 25, 2001 issue.