Mid-July is bringing the emergence of yield-robbing corn and soybean diseases and pests that Iowa farmers should be on the lookout for, experts from Iowa State University said last week.

Tar spot, a leaf disease caused by a fungus, has been confirmed in 12 Iowa counties in central and eastern Iowa. It’s recognizable by its small, slightly-raised, round-to-irregular-shaped black spots scattered across the leaf surface.

“It stops the plant from photosynthesizing efficiently, so ...