Field reports from ISU Extension crop specialists indicate that the bean leaf beetle population is now moving into emerging beans, except in the northern two to three tiers of counties. The populations appear to be fairly large in some central and southern Iowa fields and beetles are feeding on soybean seedlings as soon as they crack the soil. Fields with emerging seedlings should be scouted closely during the next couple of weeks. See last week's newsletter (pages 73-74 ) for suggestions on managing this pest and the bean pod mottle virus that it may transmit.
Bean leaf beetles also can be found in soybean stubble in fields that have not yet been planted. The occurrence of beetles in these fields is not uncommon because approximately 20 percent of bean leaf beetles overwinter in the duff of a soybean field.
Bean leaf beetles also are being found in young corn but they are not a pest of this crop. Beetles in corn may be either searching for a suitable host or simply obtaining moisture from the whorl. Corn is a poor-quality host for female beetles and for those that feed only on corn, the average life span is substantially reduced to 7-14 days compared with beetles that feed on either alfalfa or soybean. Likewise, female beetles that fed for 7 days on corn had their average rate of egg laying decreased by half; beetles that feed on corn for 14 days produced no eggs even when transferred to soybean.
This article originally appeared on pages 83-84 of the IC-486(10) -- May 21, 2001 issue.