Dissection of a V9 plant shows many ear shoots (potential ears). These develop from every above-ground node except the last 6 to 8 nodes below the tassel. Lower ear shoots grow fast at first, but only the upper 1 or 2 develop a harvestable ear. The number of kernel rows is determined by V9. The tassel begins to develop rapidly. Stalks lengthen as the internodes grow. By V10, the time between new leaf stages shortens to about every 2 to 3 days. Total number of leaves will vary from 12 to over 20 depending on hybrid maturity and genetics. Hybrids of 120-125 CRM have the most total leaves.
The potential of kernels per row is determined by V12 to V15. The top ear shoot is still smaller than the lower ear shoots, but many of the upper ears are close to the same size. This is the start of the most crucial period for determining grain yield. Upper ear shoot development overshadows lower ear shoot development. Every 1 to 2 days, a new leaf stage occurs. Silks begin to grow from the upper ears. By V17 (110 CRM), the tips of upper ear shoots may be visible atop the leaf sheaths. The tip of the tassel also may be visible. Just before tasseling silks from the basal ear ovules elongate first. Silks from the ear tip ovules follow. Brace roots (aerial nodal roots) grow from the nodes above the soil surface to help support the plant and take in water and nutrients during the reproductive stages.
- At about V10, rapid increases in nutrient and dry weight accumulation begin. This continues into the reproductive stages.
- Soil nutrient and water requirements are very high due to the increased growth rate at this stage.
- Moisture or nutrient deficiencies from V10 to V15 significantly reduce kernel numbers, ear size and grain yield.
- Earlier-maturing hybrids progress through growth stages in less time and generally produce smaller ears than later-maturing hybrids. Thus early-maturing hybrids need high plant densities for maximum yields.
- The corn plant is most sensitive to drought stress starting 2 weeks before silking until 2 weeks after silking. Grain yields are most affected from drought during that period. This is a critical period for irrigation.
- The closer to actual silking, the more yield reduction from stresses such as nutrient deficiencies or hail.
- When fields are dry avoid applications of fungicides, pesticides and associated surfactants. (Always read and follow label directions.)
- When the plant is about a week away from silking, ear development is rapid.
- Stress can delay ear and ovule development more than tassel development. Such a delay would mean a lag between pollen shed and silking. Severe stress may delay silking until after pollen shed, resulting in unfertilized ovules.
- Damage (arrested ear development) has been reported from fungicide applications that included non-ionic surfactants prior to tasseling.
GDUs Required** to reach V9 growth stage depends on maturity and is approximately:
** Hybrid growth is influenced by the growing environment. Individual results may vary.
||Larval feeding is most extensive in early through mid-July in most regions of the Corn Belt.
|European Corn Borer
||As the true stalk develops and European corn borer larvae increase in size, larvae can be found tunneling into the stalk.
||V6 through R4. Disease primarily found in northern environments.
||VE through R6. Disease primarily found in Nebraska and portions of other western states.
Click on the insect or disease for more information.
* Information from Pioneer and Iowa State University Extension.