Timely rains vital for corn crop

Crops in the area are now in the home stretch. Final yields will be heavily determined by August rains.
If rains are timely, yields will be high. If short, just OK.
Periods of cool temperatures during the past month have caused some farmers to be concerned about a delayed harvest or early frost. However, most of the corn in the area tasseled and pollinated sooner than most years.
Pollination time is a very critical time for the success of a corn crop. At this time, the crop is vulnerable to heat and moisture stress. Too much stress may cause poor pollination, leading to reduced yields.
Weather conditions were ideal for pollination in most of the area, that is, moderate temperatures and adequate soil moisture.
The corn plant, like us, does not like temperatures over 90 degrees.
Photosynthesis in corn is the most active at afternoon temperatures in the low 80s. The plant will protect itself by closing stomata, the leaf openings for gas exchange, when temperatures are above 90 degrees. Above 86 degrees, respiration losses will exceed photosynthesis gains, thus the closing of stomata.
Photosynthesis does not occur during the night. However, respiration, which is an energy user, still occurs.
Generally, the plant produces more energy during the day than what it loses at night.
The more energy it can store during the day and the less loss at night allows more for the developing grain. Thus, more energy is available for grain development during cooler night temperatures.
The ideal situation for grain development in corn is a bright sunny day with temperatures in the low to mid-80s and night temperatures in the 50s.
Dry days with temperatures above 90 will hasten the maturity of corn, but it will also lower the yield potential, as will hot night temperatures.
Most of the corn in the area is in the R2 to R3 growth stage. Kernels will be like blisters, filled with clear liquid, in the R2 growth stage and the liquid will become milky in the R3 stage.
Agronomists use a two-letter designation for corn growth stages. They use the letter V and the corresponding leaf number for the vegetative stages. Once the silks on the ear become visible the system switches to reproductive stages designated by the letter R.
When the silks first become visible, corn is in the R1 growth stage or silking stage. The later reproductive stages are physical descriptions of the kernels.
Thus R2 is the blister stage, R3 is the milk stage, R4 is the dough stage, R5 is the dent stage, and R6 is physiological maturity.
The corn plant produces no more leaves once the tassels are visible. Silks generally emerge soon after the tassels emerge. The potential number of kernels per ear has been established by tasseling.
The corn plant may reduce the number of kernels from R1 to R3 if environmental conditions trigger hormones in the plant of potential stresses that may affect kernel success. These aborted kernels are visible on the tip of the ear.
Stresses include soil moisture, inadequate nutrients, light competition, and pest damages. Most plants do not have kernels developed to the tip of the ear.
Often, yields will be larger per acre with ears that are not filled to the tip but about an inch back, an optimum balance among plant population, soil moisture, and available nutrients. Yields are larger because of more ears per acre and less kernels per ear.
After the growth stage R3, the only way the corn plant can adapt to environmental stress is to reduce kernel weight. Generally, moisture stress is a major environmental factor that reduces kernel weight.
Besides the lack of water, moisture stress also reduces the flow of nutrients to the plant.
Thus, timely rains will be needed for the rest of the growing season to ensure good grain fill for plump kernels. Most of the corn has a good root system this year to pull moisture from deeper depths, but a quarter- to a half-inch of rain every 10 days until maturity would be beneficial.
Corn in the area has the potential for very good yields at this time.
Farmers need every bushel they can get for profitability since the grain market prices have been dropping. Timely rain events and afternoon temperatures in the 80s should provide conditions for excellent yields.
Lentz is extension educator for agriculture and natural resources for The Ohio State University Extension Service in Hancock County. He can be reached at 419-422-3851 or via email at
Lentz can be heard with Vaun Wickerham on weekdays at 6:35 a.m. on WFIN, at 5:43 a.m. on WKXA-FM, and at 5:28 a.m. at 106.3 The Fox.



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