A key factor in yield is pollination success. Across the Cornbelt, field corn enters the critical period of pollination from late June through the end of July. A corn plant is monoecious, which means it contains both male and female flowers on the same plant. The female flower is called the ear and contains the ovules and silks. The male flower is called the tassel and sheds pollen. Many understand the female flower and its importance in yield, but let’s dive deeper into the male flower.
The tassel sits at the top of a corn plant. Each tassel consists of a central tassel stalk and lateral branches. Around 1,000 spikelets are formed on each tassel bearing two small florets. Inside each floret are three anthers that produce thousands of pollen grains. The yellow pollen that falls from these anthers contain the male genetic material to fertilize the ovary of one potential kernel on the ear. Pollen shed starts in the middle of the main tassel and progresses up, down, and to additional branches over time. After releasing pollen, empty anthers will shed and eventually drop from the tassel.
Industry research estimates a single tassel can release two to 25 million pollen grains. Due to its thin outer membrane and high moisture content, pollen is only viable for a few minutes. Yet, in this time frame, a pollen grain can travel up to .5 miles with a 15 mph wind. (This is why seed corn fields and IP (identity preserved) markets require knowledge of neighboring crops and removal of border rows to reduce pollen “drift” and maintain quality).
Weather plays a key part in pollination. High temperatures, extreme weather events, and drought stress can have detrimental effects on pollination success and yield. At VT (tassel), all leaves are exposed, and the plant has reached its maximum height. Hail events at this point, or after, can cause up to 100% yield loss. Even successfully pollinated ears can be aborted after hail due to defoliation.
With corn pollen being viable for only a few minutes, extreme temperatures and dry conditions can lead to poor pollination. Naturally, the corn plant releases pollen from early to mid-morning and again around late evening, escaping the heat of the day. Temperatures greater than 100° F can kill pollen. Drought and heat stress can induce anthers to speed up pollen release, so severe pollination issues occur when tassels shed before silks are available, missing the “nick.” To combat a failed pollination “nick,” corn breeders study and select for hybrids that silk first for growing areas that face annual heat and drought stress.
Rain during pollination is a common occurrence. Many farmers wonder what effect it will have on pollen shed and fertilization. But, just like with warmer temperatures, a tassel will delay pollen shed if it becomes too wet. This means there will be little to no pollen on the silks being washed off.
Silks will detach from fertilized ovules; we can monitor pollination with a quick test. Carefully make one long cut from the base to the tip of the ear and unwrap the husk leaves, making sure not to pull any silks away. While holding the base of the ear gently shake. Detached silks are signs of successful kernel pollination.
Pollination is mostly out of our control, but we can spread out the risks with hybrid choices and diversifying planting dates. Fungicide application is a PFR Proven™ practice that when applied during this critical point in a corn plant’s life, at the VT growth stage, can help reduce disease, plant stress, and maximize yield.
~ Travis Coleman – Field Agronomist