Reports of yellowing in small grains have started to reach me. There are several reasons why young wheat, barley, or oat plants have a pale green/yellow color. Some of the more common causes of early season yellowing are:
§ Nitrogen deficiency
§ Sulfur deficiency
§ Early tan spot infections
§ Herbicide injury
§ Barley yellow dwarf virus (BYDV) infections
Nitrogen (N) deficiencies can readily be identified as the symptoms are worst on the oldest leaves and start at the tip of the leaves, progressing towards the base as the deficiency gets worse. The causes of the N deficiencies are several, all which have common denominator, namely excess precipitation. Excessive rainfall causes leaching, denitrification, and an inability of the plants to take up available N.