Sufficient soil moisture essential for corn

TABER, Alta. — The next two weeks are crucial in the life of southern Alberta corn plants.

The thirsty crop will use six milli-metres of moisture per day once plants reach the tassel stage, so producers need to keep up with their irrigation plans.

“As we move into this tassel time … that’s the highest peak water demand for the crop, all through the silking and pollination phase and a little bit after,” said DuPont Pioneer agronomist Nicole Rasmussen.

Corn roots can extend a metre deep, but 70 percent of the moisture is extracted in the top half of the root zone. As a result, adequate soil moisture must be maintained at the 45 centimetre level, she told growers at a July 23 corn school.

“We don’t want a flooded root zone, (but) we’ve got to make sure that we’re planning to keep that root zone as even as we can,” said Rasmussen.

Corn in southern Alberta is at or near the tassel stage, after which silk begins to develop. The silks are 90 percent water and need moisture to develop and accept pollen.

“If those silks get a little wilted, the pollen can’t travel down them, and you’ll get a missing kernel, and every missing kernel is a take away from your yield, whether you’re a silage grower or a grain grower or a grazing customer.”

Silks will grow 2.5 to four cm per day in optimum conditions, starting at the base of the ear, said Lloyd Van Eeden Petersman, an independent DuPont Pioneer representative.

The sticky silks will continue growing until they are pollinated.

Then it takes about 24 hours for the pollen grain to travel down the silk tube, ovulate and begin forming a kernel of corn.

The silk begins to dry and brown off once fertilization has occurred.

Each corn tassle produces half a million pollen grains a day, so there are few worries about adequate contact of pollen with the silks, said Van Eeden Petersman.

Rasmussen urged producers to avoid major fluctuations in soil moisture, and keep moisture capacity of at least 75 percent.

“It’s the most critical time for your yield right now, going into pollination,” she said.

“If you’re behind going into this phase, I don’t know too many irrigation systems that can refill that soil profile back up.”

She also cautioned growers not to stop irrigating too early, despite the temptation to allow fields to dry for truck traffic during harvest. Yield can suffer even at the later stages of development.

In general, the southern Alberta corn crop is thriving. A recent spate of hot weather has provided 22 to 23 heat units per day since July 1. Most grain corn requires 2,100 to 2,300 heat units to reach maturity, and the total is now around 1,300.

Corn crops went from waist high to more than two meters during the middle two weeks of July, said Van Eeden Petersman.

“Plant stress from basically where we’re at now, going into the tassel, carrying on into the early stages of reproduction, it’s very important that we have our water up where it needs to be and stay away from any funny herbicide timings,” he said.

“We have to be careful what we do.”

There has been little evidence of insect pressure. Grasshopper damage is minimal but European corn borer is always a threat.

Corn borer moths are the white, dusty looking insects seen in early evening. They lay eggs in small milky patches on the undersides of leaves.

Once hatched, the worms burrow through curled leaves, creating shot holes. They also eat into stalks, reducing nutrient flow.

B.t. corn varieties kill the worms, preventing second and third generations.

“As we get more and more corn in the area, we need to stay on top of that, managing our insect pressures with the genes and traits that are available,” said Van Eeden Petersman.

He also said poor irrigation water quality can cause bacterial rot. Symptoms include a discoloured leaf on a plant that, when removed, has a rotting smell. It may not kill the plant but will affect yield.

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