Source: Jim Shroyer, Extension Agronomy State Leader, Kansas State University
Wheat in Kansas currently ranges from late jointing (Feekes 7) or flag leaf emergence (Feekes 8) to the boot (Feekes 10) or early heading (Feekes 10.2) stages of growth.
At Feekes 7, there are two nodes visible on the stems. Shortly after the second node is visible on the stem, the flag leaf will begin to emerge. This is Feekes 8. The flag leaf is the last leaf the stem will produce. Generally, the flag leaf will first become visible when you can see two nodes on the stem. At this point, the young head will be inside the stem, where the second leaf below the flag leaf attaches to the stem. It may be difficult to feel the head within the stem at this stage, but it can be seen by cutting open the stem.
Shortly after the flag leaf begins to emerge, it will begin to extend to its full length. The flag leaf contributes about 75 percent of the nutrients that go into the wheat kernels. Producers should try to keep the flag leaf healthy because leaf diseases can damage leaves and grain yields will be reduced.
This is about as late as producers should apply 2,4-D for weed control. Most of the sulfonylurea herbicides can still be applied until boot stage, but ideally should be applied before flag leaf emergence. Between the time the flag leaf has extended and early heading, foliar fungicides can be applied if needed. Any nitrogen applied at these stages of growth can increase protein levels in some cases, but would only increase yields if the plants are extremely deficient in nitrogen.
The head continues to push upward in the stem after the flag leaf has reached its full length. Soon, you can feel a bulge in the stem just below the flag leaf. At this stage (Feekes 10, or boot stage), the head is about to emerge from the whorl and producers can see awns emerging.
In two weeks, we will have an article talking about the important head emergence and flowering stages of development.