Richard Taylor, Extension Agronomist;rtaylor@udel.edu
As we transition into May, the small grain crop will soon reaching heading and enter the booting stage followed by head emergence. Recognizing the actual growth and development stage is critical for fungicide applications since timing is so important when applying these products. Before the crop actually reaches these important reproductive stages, it will be worth your time to review descriptions of the actual stages.
There are two scales that describe growth and development that are commonly used by consultants and agronomists. The first scale is the Feekes’ scale most often used in the United States. It is a numerical scale and begins at 1.0 and ends at 11.4 with 1.0 representing when the first leaf is visible through the coleoptile of the germinating seed and 11.4 representing a mature plant ready for harvest. Second is Zadoks’ scale which some consultants use but is more often used in Europe. Zadoks’ scale is a decimal code for the growth stages of cereals and goes from 00 to 100 with 00 representing dry seed and 100 representing a mature crop ready for harvest. In the discussion below, I’ll use both scales indicating first the Feekes’ scale and then in parentheses the Zadoks’ scale code.
I will start at the early boot stage which is between 9 and 10 on the Feekes’ scale (Zadoks’ 40). At this stage the observer can detect the flag leaf sheath extending out of the leaf below the flag leaf. This stage is called the early boot stage. Feekes’ stage 10 (Zadoks’ 45) occurs when the boot is swollen. The boot is the enclosed leaf sheath below the emerging flag leaf and it becomes swollen as the seed head or inflorescence begins to expand and move up through this leaf sheath (See Photo 1). Although inflorescence is the scientific term to describe the wheat seed head with all its spikelets and flowers, I think most producers and consultants would prefer to call it the wheat seed head and I will use that term below to indicate the wheat inflorescence.
Photo 1. Early- to mid-boot stage in soft red winter wheat showing the seed head causing a swelling of the leaf sheath in which it is growing. Note the internode elongation above the node where the flag leaf attaches to the main stem.
Photo 2 illustrates the end of the boot stage as the seed head is about to emerge from the leaf sheath of the flag leaf. In awned wheat varieties, this stage is easily detected since the awns precede the seed head but in non-awned varieties, the stage is often indicated by the leaf sheath splitting partially open below the leaf collar (the junction of the leaf blade and the leaf sheath which is often a pale yellowish-white color and is where the observer can see the auricles of the leaf). This is still considered Feekes’ stage 10 but is Zadoks’ stage 47 to 49.
Photo 2. Although this photo is of a cereal rye plant, it does show how at the end of the boot stage in awned varieties, the awns will emerge from the leaf sheath of the flag leaf.
The next few stages refer to the emergence of the seed head. Because wheat plants in a field will not all emerge from boot stage at the same time, the following subdivisions apply or are assigned to a field when 50 percent of the plants have reached the decimal designation described below. At Feekes’ 10.1 (Zadoks’ 50) the very first spikelet of the seed head is just visible emerging out of the leaf sheath and collar of the flag leaf. When one quarter of the seed head is visible above the flag leaf collar, the plant has reached Feekes’ 10.2 (Zadoks’ 52). When one half of the seed head is visible above the flag leaf collar, the plant is now at Feekes’ 10.3 (Zadoks’ 54). At three quarters emergence the growth stage moves to 10.4 (Zadoks’ 56). The wheat field is said to be at Feekes’ 10.5 (Zadoks’ 58), when the seed head has emerged completely and is above the collar and auricle of the flag leaf on 50 percent of the plants in the field.
The development of winter wheat from the end of Feekes’ 9 (Zadoks’ 39) when the flag leaf ligule and collar is just visible out of the next lower leaf sheath to the beginning of flowering or Feekes’ 10.5.1 varies depending on the weather conditions but generally will occur during a 9 to 16 day window. Anthesis or beginning of flowering which is Feekes’ 10.5.1 (Zadoks’ 60) usually is detected when anthers begin to emerge from out of the spikelets (Photo 3 and 4). Feekes’ 10.5.1 is considered the optimum time to apply fungicides to suppress Fusarium head blight (scab).
Photo 3. Wheat seed head at beginning of flowering with pollen-containing anther visible near the center of the seed head.
The Feekes’ scale does not differentiate stages within flowering as does Zadok’s scale. Zadok’s scale designates the beginning of anthesis as 60, anthesis occurring half-way over the seed head as 64 (Photo 4) and anthesis complete as 68. Once flowering begins, pollination is completed in about four to five days which some sources refer to as Feekes’ 10.5.3.
Photo 4. Wheat seed head about half-way through anthesis or flowering showing the emerging anthers.
Once flowering is complete and pollination has occurred, the crop enters the ripening stage beginning with Feekes’ 10.5.4 (Zadoks’ 71) which is when the wheat kernels are watery ripe. When the watery consistency changes to a milky consistency and there’s a notable increase in the solids of the liquid endosperm when the seed is crushed between the fingers, the crop has reached Feekes’ 11.1 (Zadoks’ 75). It often takes several weeks to complete the ripening process and timing is somewhat weather dependent.