Know when to say when on corn yields

Chad Lee, Extension Agronomist, University of Kentucky

While many farmers have already given up on the corn crop this season, others are waiting a little longer. Identifying the success of pollination in a field can go a long way to determining whether or not to give up grain yield goals.

Figure 1. Pollination on this plant is completed
based on  the exposed stamens. A shake of
the tassel shows no evidence of additional pollen. 

Anthers fully exposed across the entire tassel indicates that pollination is nearly complete (Figure 1). Pollen release normally begins near the middle of the tassel and then upwards and downwards. If the plant is still pollinating, a gentle shake of the tassel should release some of the small pollen grains. If there are no pollen grains, then pollination is probably complete.

Brown silks on are an indication that pollination is complete as well (Figure 2). These indicators are important, because in many fields, pollen drop has occurred before silk emergence.

Gently cutting open the husks around the ear can reveal the silks and developing ear. Once pollen travels down the silk and fertilizes and ovule, the silks detach from the young kernel. A gentle shake of the ear will help you identify the amount of pollination that has occurred. As kernel development progresses, identifying pollination success becomes easier. Developing kernels are easy to see (Figures 3 and 4) while the blanks are easy to see as well. An ear where all almost all kernels are developing is evidence of excellent pollination (Figure 5).

Temperatures near 100 F can kill pollen. Since June 28, 2012, many corn fields in Kentucky, including the ones in these pictures, have experienced seven days above 100 F.  Pollen drop normally occurs for about a week or two. However, peak pollination is normally about the third day of pollen drop. Based on the ears in Figures 3 and 4, pollination was severely impaired by the high temperatures. In both of these cases, those ears represented less than half of the ears in the field. The other half had not released silks, yet. With pollination complete in those fields, that means that half of the ears will not be fertilized at all. In fields such as these, salvaging the crop as a silage is probably the best option. Be sure to check with your crop insurance agent before making any decision to cut the crop for silage. 



Adding insult to injury, those fields received a little over 1 inch of rain yesterday and temperatures have now dropped into the mid 80 s F. In other words, about one week after pollination, the weather is now ideal for pollination. Corn planted later and just now going through pollination still has a chance to make excellent yields. Based on the latest USDA-NASS crop progress report, 66% of the corn was silking last week.That leaves a small percentage of corn acres in Kentucky that have a chance to make decent yields.   

Figure 2. Brown silks indicate that
pollination is complete. 

Figure 3. Pollination is done in this field and about
half of the ear was not fertilized.  Less than 20% of the ears
in this field looked this good. 

Figure 4. Pollination is complete in this field and
 less than 10% of the ear was fertilized.
This ear has almost no yield potential. 

Figure 5. This ear has excellent yield potential,
with excellent fertilization.