High Day Temperatures and Corn Pollination

Chad Lee, Extension Agronomist, University of Kentucky

Corn pollen drop is
occurring in many fields. 

Much of the corn in the state is going through pollination right as daytime temperatures are the highest for the season. Fortunately, most pollen drop occurs earlier in the morning and some occurs later in the evening. Soon after pollen comes into contact with silks, it begins pollen tube growth in those silks. As long as morning temperatures stay in the low 70's, pollination should occur without much trouble. Last year, morning temperatures were in excess of 90 degrees, relative humidity was low, the soils were extremely dry and the corn was under severe drought stress. This year, humidity is accompanying the hotter temperatures. The higher humidity will help the viability of the pollen grains.

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. 

Drought Stress and Corn Pollination

Chad Lee, Extension Agronomist, University of Kentucky

Drought-stress corn in western Kentucky. Photo: June 25, 2012. 

Most of western Kentucky is in a severe drought status and that severity is likely to spread to central Kentucky on the next report. Most of the corn is going through tassel and pollination, which is well ahead of the five-year average, and the worst possible time to experience temperatures in the high 90's F (35 C or more). The high temperatures and low humidity dry out pollen and silks faster, both of which need moisture for successful fertilization of the ovules.

In addition to the need for moisture for pollination, the corn plant simply needs more water. Corn around tasseling and silking demands about 0.3 inches (7.7 mm) per day. Most of our fields were at a water deficit prior to tasseling and the water deficit is increasing. The lack of water could lead to the abortion of kernels.

Dry conditions prior to tasseling often result in the tassel emergence and pollen drop before silk emergence. In many cases, the resulting ears may have a few kernels develop near the base of the ear but very few to no kernels near the tip of the ear.

Bad Pollination - Heat a Culprit

Chad Lee, Extension Agronomist, University of Kentucky

Now is a good time check fields for pollination problems. The high temperatures may have caused problems in some fields. See the images below. While we don't expect all fields to look like this, some will. Scouting now will help producers identify some options for this fall (even if the only options left are in marketing).

The blank kernels on these ears are from poor pollination. Heat stress is the most likely culprit. Image source: Nick Roy, Extension Agent, Adair County, Kentucky.

The blank kernels on this ear are the result of poor pollination. Heat stress is the most likely culprit. Image source: Nick Roy, Extension Agent, Adair County, Kentucky.

Check Corn for Pollination and Seed Set

Cory Walters just posted an article about how good prices look right now for corn. In addition, the corn crop looks great from the road. But before you decide to contract that rest of your expected yields, get into the fields and make sure pollination went well.

We have received several reports from county agents of fields with poor pollination. Perhaps the most unsettling report came from Tom Miller, Extension agent in Ballard County, who said that pockets of a field had poor pollination. Plants in the same row had good pollination while others had terrible pollination. (One of his images is attached to this article.) At this point, hot dry weather and slight variations as to when pollen drop occurred appears to be the best explanation. This is unsettling, because the whole field looks excellent from the road.

So, if the silks are dry, then pull back the husks and look at the developing "blisters" or seeds. You know how a good ear of corn should look... even number of rows, pollination from the base to the tip of the ear.

If the silks are still wet, but pollen drop appears to be complete, then you can gently remove the husks and get an estimate of pollination. To do this, make a cut through the husks with a sharp pocket knife along the ear. Start at the base of the ear and slice up to the tip. Make a second slice on the other side of the ear. If you have done a good job making the slices, you should be able to gently pull off the husks without removing the silks. If silks come off with the husks, then get a new ear and start over.

Once you have successfully removed the husks and kept the silks on the ear, hold the ear at the base and gently shake it. You may want to point the top of the ear towards the ground. As you gently shake, silks will fall from the ear if pollination has occurred. Again, you are hoping for all of the silks to fall from the ear. Pollination normally occurs from the base of the ear and then moves toward the top. If you happen to get an ear where the silks near the base fall off, but the silks near the top do not, then pollination may not be complete in the field.