Dry weather and other factors can cause wheat to be yellowish or pale in the fall, instead of a nice, healthy green. When that happens, producers want to know why, said Jim Shroyer, K-State Research and Extension crop production specialist.
Shroyer said the common reasons for yellow wheat in fall are:
* Poor root growth. This may be due to dry soils or poor seedbed conditions at planting time. If the plants have been emerged for several weeks or more and if they can be pulled up easily and have only a couple primary roots visible, then the plants’ root systems are not extensive enough to provide enough nutrients.
* Nitrogen deficiency. Nitrogen deficiency causes an overall yellowing of the plant, with the lower leaves’ dying from the tips inward. Nitrogen deficiency in the fall also results in reduced tillering, top growth and root growth. The primary causes of this kind of nitrogen deficiency are insufficient fertilizer rates, leaching from heavy rains, and the presence of heavy amounts of crop residue that immobilize nitrogen.
* Leaf rust or tan spot. If leaf rust infects young seedlings in the fall, the plants may turn yellowish; fall infections of leaf rust are not common in Kansas but can occur. Tan spot also can cause wheat to turn yellow in the fall. Treating fields in the fall for leaf rust or tan spot rarely if ever pays, even if those diseases do cause yellowing, because cold temperatures in the winter normally cure the problem.
* Low temperatures. When temperatures are quite cold at the time wheat emerges, the result can be yellow banding on the leaves. If so, the symptoms should eventually fade away.