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Corn Pollination During Drought

Categories: GROWING, CORN
​​​​​​​According to Purdue University, stress during silk emergence and pollen shed can cause more yield loss than almost any growth and development stage.  At this stage, inadequate plant water potential can hinder pollination of the kernel ovule.  During the silking and pollen shed period, severe drought may reduce yield from 3 to 8% per day. During the 2 weeks following silking, extreme stress may further reduce yield up to 6% per day.

Silk Emergence
Severe drought stress, as indicated by wilting of the corn plant, affects pollination primarily by its impact on silk elongation. Silks begin elongating from the ovules, or potential kernels, of the ear shoot about 7 days before silks are visible outside the husk tips. The silks from the butt of the ear elongate first, followed by those in the center and then the tip. Water stress around flowering and pollination delays silking, reduces silk elongation, and inhibits embryo development after pollination. Moisture combined with heat stress interferes with the synchronization of silk emergence and pollen shed. 

Drought stress may desiccate silks leaving them unreceptive to pollen and the chance to fertilize the ovule. The tip silks are typically the last to emerge from the husk leaves, and if ears are longer than usual, the final silks from the tip of the ear may emerge after pollen shed. If severe drought stress continues into early kernel development, abortion of fertilized ovules can also result in an incomplete kernel set. Aborted kernels are shrunken, mostly white and different from unfertilized ovules in that development had already started.

Pollen Shed
In typical field conditions, an individual pollen grain will remain viable for 1 to 2 hours, but high temperatures with low relative humidity can rapidly degrade pollen. Temperatures at 100o or above may literally kill pollen. Fortunately, pollen shed typically occurs during early to mid-morning hours before temperatures climb to such dangerous heights. “Fresh” pollen occurs over a few days until maturation is complete. If there’s enough soil moisture to meet the plants’ needs, pollination can still be successful during lengthy periods of high temperatures. 

The University of Wisconsin Extension suggests 2 techniques to assess the success or failure of pollination. One popular method is the "shake test." Carefully unwrap the ear husk leaves and gently shake the ear. The silks from fertilized ovules will drop off. The proportion of silks dropping off the ear indicates the proportion of future kernels on an ear. Randomly sample several ears in a field to estimate the success of pollination. The second technique is to wait until 10 days after fertilization of the ovules. Healthy developing kernels should appear as watery blisters during the R2 development stage.

Harvest Recommendations
If pollination is good despite the heat, keep your plan to harvest as usual. When pollination is poor but some kernels are developing, the plant can continue to gain dry matter, and it is still possible to harvest your crops. In some areas, you can harvest poorly pollinated fields for silage use. During extreme situations of no pollination, the best quality forage will be found as close to flowering as possible. You could also leave the crop as a living cover crop until the fall before mowing or chopping.

To help make the most of available moisture next season, consider planting Agrisure Artesian® hybrids. Artesian corn hybrids contain multiple genes for season-long drought protection, responding to water stress with multiple modes of action—including at pollination, to maximize yield when it rains and increase yield when it doesn’t.

Contact your Golden Harvest Seed Advisor with questions or for additional agronomic insights.

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