Mid-season corn crop evaulations

Silking corn received some much needed precipitation over the last forty-eight hours across much of Salem County. On a hot July day, corn in pollination mode can easily uptake .25 to .30 inches of moisture. Depending on the location, some fields only received a day’s worth of rain while other’s under the path of the northeasterly tracking storms received upwards of .80 inches this weekend.

Curled leaves of corn waiting for rainfall

Evaluating field water holding capacity. Precipitation is critical to mazimizing grain fill on soils with low water holding capacity under these conditions. Soil compaction in fields that are exhibiting classic surface sealing are exasperating corn moisture stress conditions as seen in this July 23^rd photograph. Combined with the high evapotranspiration rate of the last two weeks, these soils are unable to absorb or retain enough moisture to meet crop removal needs. Now is a good time to evaluate soil water holding capacity and tilth condition and how well the corn hybrid planted on that soil met expectations despite any pressure from silk feeding insects.

When moisture stress occurs makes all the difference. Remember, corn hybrids mature at different times based on their individual need to accumulate heat units. Just before silking is visible, corn plants are in the V12 collar stage. At this stage, one can assume at least 880 heat units since planting at this location. At V12 stage, we can assume the crop emerged 43 to 50 days ago. When fifteen collars are present, the crop is about ten days away from silking. This is when ear size, kernel size and kernel number are determined. Take a moment to look back and see what maturity corn was planted. Do you like what you see? Despite the weather stress? If counting leaves, their should be at least sixteen leaves on the plant before the tassel appears on shorter season hybrids and as many as twenty-one on longer season hybrids.

What happens at silking? Did you know that at silking, 50% of the available nitrogen and phosphorus in the soil is taken up by the crop over the next few weeks. When did you put down nitrogen? Sixty days ago as a plow down but with a delayed planting? Forty days ago at planting? Twenty days ago as a side-dress? Did you split applications?

How many days are left to physiological maturity? An ‘85 day’ corn requires about 2100 heat units since planting to mature. ‘101’ day corn varieties require more than 2400 heat units. It’s the end of July. How many heat units are left in the growing season to reach physiological maturity based on the V stage of the crop? Given the soil moisture holding capacity of the soil, could you have planted that field any earlier? Planted it later? Used a longer or shorter maturing variety? If the planting date had remained the same, would a shorter day or a longer day corn have pollinated better or faired worse given the precipitation pattern at that locale? What if the planting date had been earlier, or later? How did tillage choice impact water holding capacity of that soil?

What next? While a typical field of corn can take up to fourteen days to reach full pollination, some of the crop wil be pollinating every day. This is actually a good thing. Pollen only sheds when anthers are dry and extreme heat can even kill pollen. Corn is wind pollinated. When shed, the pollen clouds will drift from twenty to fifty feet. Last week’s low air quality rating due to the smokey haze over the region was also due in part to the amount of corn pollen in the air locally. Conversely, on overcast rainy days, tassles do not release pollen to the silks below. Too much wind during pollen shed can actually blow the pollen beyond reach.

Lastly, while the silks are being pollinated they have to compete with japanese beetles, corn beetles and a myraid of other silk clipping insects.

If you can tolerate the smell and feel of corn pollen on your eyelashes, put on a rain coat and go for a walk through your crop to see how the interior of the field is fairing this season. Remember as hay comes off and soybeans are sprayed, the bugs are seeking haven in corn.