The flax and barley were smitten Which were not so necessary for human life as the wheat and rye. Thus God sends smaller judgments before the greater. The flax was bolled Grown into a stalk.
Related Commentaries of Exodus 9:31
Exodus 9:31
31 And the flax and the barley was smitten: for the barley was in the ear, and the flax was bolled.