Rain Not Likely To Halt Pollination

Expert says there is little chance that pollen is washed off silk when tassel is wet.

Published on: Jul 30, 2013

You would be amazed at how much the scientists know about pollination. Peter Thomison, Ohio State University agronomist, addressed some of the fine details of pollination in comments made last week in C.O.R.N. Newletter.

Most importantly: Will the heavy, protracted rainfall and root lodging which has occurred recently in some areas adversely affect pollination?

ThomisonPollen shed is not a continuous process. It stops when the tassel is too wet or too dry and begins again when temperature conditions are favorable. Pollen stands little chance of being washed off the silks during a rainstorm as little to none is shed when the tassel is wet. Also, silks are covered with fine, sticky hairs, which serve to catch and anchor pollen grains. Most root lodged corn has recovered with the upper portions of plants resuming a vertical growth pattern through "goosenecking" so negative effects on pollination should be limited.

Rain Not Likely To Halt Pollination
Rain Not Likely To Halt Pollination

How does the timing work?
Thomison: Most corn hybrids tassel and silk about the same time although some variability exists among hybrids and environments. On a typical midsummer day, peak pollen shed occurs in the morning between 9:00 and 11:00 a.m. followed by a second round of pollen shed late in the afternoon. Pollen may be shed before the tassel fully emerges.

Where does this happen?
Thomison: Pollen shed begins in the middle of the central spike of the tassel and spreads out later over the whole tassel with the lower branches last to shed pollen. Pollen grains are borne in anthers, each of which contains a large number of pollen grains. The anthers open and the pollen grains pour out in early to mid morning after dew has dried off the tassels. Pollen is light and is often carried considerable distances by the wind. However, most of it settles within 20 to 50 feet. 

How long do you have for pollination to take place?
Thomison: Under favorable conditions, pollen grain remains viable for only 18 to 24 hours. However, the pollen grain starts growth of the pollen tube down the silk channel within minutes of coming in contact with a silk and the pollen tube grows the length of the silk and enters the female flower (ovule) in 12 to 28 hours. A well-developed ear shoot should have 750 to 1,000 ovules (potential kernels) each producing a silk. The silks from near the base of the ear emerge first and those from the tip appear last. Under good conditions, all silks will emerge and be ready for pollination within 3 to 5 days and this usually provides adequate time for all silks to be pollinated before pollen shed ceases.