Farmers say soybean yields are OK despite very low moisture content, but disease pressure has led to disappointing corn yields in many areas. 

With warm and dry weather the past two weeks, harvest is moving along quickly in Iowa. But in many cases, farmers say corn yields are coming in below expectations, as what was thought to be a history-making crop has shrunk due to disease pressure.

Unseasonably warm temper­atures, nearing 90 degrees in some parts of Iowa during the first week of October, are also zapping moisture out of soybeans and causing yield...