Wednesday, June 27, 2012

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.

Drought-stress from at the
edge of an irrigated field. 
Irrigated corn with little water stress.
This is in the same row as the corn
in the previous image. 
Two corn ears from the same hybrid and  row in the field.
The smaller ear is not irrigated.
The larger ear is irrigated. Rows of kernels are the same (14) but length of rows are different. This water stress started when row length was being determined. 

In other cases, the tassels may drop pollen before they are fully emerged from the whorl. If the silks are emerged, pollination may occur. If too much of the pollen is trapped in the whorl, then pollination will suffer.

Tassel mostly in the whorl, but dropping pollen. 
Moist silks are a must for good pollination.

Corn yield losses should be expected in most of these fields. The potential number of kernels was beginning to be determined somewhere around V8 growth stage. As the dry weather stressed the corn crop, the potential number of kernels dropped. Expected complications with pollination increases the probabilities of lower yields.

In some of the fields exhibiting the most severe drought stress conditions, farmers may want to look at salvage opportunities such as feeding the corn as a silage. Proper ensiling requires the proper whole plant moisture (around 65 to 70% for most ensiling conditions). This season, whole plant moisture is more important than crop stage to deciding when to harvest.

Related Articles:
The next big hurdle: pollen shed and silking
Irrigation Management for Corn


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